chore: don't fail on running build bench on built stage3 (#13467)

This PR applies two minor tweaks:
- `tests/bench/sym/simp_1.lean`: share-common the proof term before
counting objects in `getProofSize`, so the reported size reflects the
shared representation.
- `tests/elab/sym_simp_3.lean`: use `>>` instead of `.andThen` when
composing `Sym.Simp` methods.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -279,7 +279,8 @@ jobs:
                 "os": large ? "nscloud-ubuntu-24.04-amd64-8x16-with-cache" : "ubuntu-latest",
                 "enabled": true,
                 "check-rebootstrap": level >= 1,
-                "check-stage3": level >= 2,
+                // Done as part of test-bench
+                //"check-stage3": level >= 2,
                 "test": true,
                 // NOTE: `test-bench` currently seems to be broken on `ubuntu-latest`
                 "test-bench": large && level >= 2,
@@ -291,7 +292,8 @@ jobs:
                 "os": large ? "nscloud-ubuntu-24.04-amd64-8x16-with-cache" : "ubuntu-latest",
                 "enabled": true,
                 "check-rebootstrap": level >= 1,
-                "check-stage3": level >= 2,
+                // Done as part of test-bench
+                //"check-stage3": level >= 2,
                 "test": true,
                 "secondary": true,
                 // NOTE: `test-bench` currently seems to be broken on `ubuntu-latest`

AGENTS.md

@@ -0,0 +1 @@
+.claude/CLAUDE.md

CMakeLists.txt

@@ -129,6 +129,7 @@ if(USE_MIMALLOC)
     # cadical, it might be worth reorganizing the directory structure.
     SOURCE_DIR
     "${CMAKE_BINARY_DIR}/mimalloc/src/mimalloc"
+    EXCLUDE_FROM_ALL
   )
   FetchContent_MakeAvailable(mimalloc)
 endif()

src/CMakeLists.txt

@@ -110,6 +110,7 @@ option(RUNTIME_STATS "RUNTIME_STATS" OFF)
 option(BSYMBOLIC "Link with -Bsymbolic to reduce call overhead in shared libraries (Linux)" ON)
 option(USE_GMP "USE_GMP" ON)
 option(USE_MIMALLOC "use mimalloc" ON)
+set(LEAN_MI_SECURE 0 CACHE STRING "Configure mimalloc memory safety mitigations (https://github.com/microsoft/mimalloc/blob/v2.2.7/include/mimalloc/types.h#L56-L60)")
 
 # development-specific options
 option(CHECK_OLEAN_VERSION "Only load .olean files compiled with the current version of Lean" OFF)
@@ -117,6 +118,7 @@ option(USE_LAKE "Use Lake instead of lean.mk for building core libs from languag
 option(USE_LAKE_CACHE "Use the Lake artifact cache for stage 1 builds (requires USE_LAKE)" OFF)
 
 set(LEAN_EXTRA_OPTS "" CACHE STRING "extra options to lean (via lake or make)")
+set(LEAN_EXTRA_LAKE_OPTS "" CACHE STRING "extra options to lake")
 set(LEAN_EXTRA_MAKE_OPTS "" CACHE STRING "extra options to leanmake")
 set(LEANC_CC ${CMAKE_C_COMPILER} CACHE STRING "C compiler to use in `leanc`")
 
@@ -126,7 +128,7 @@ string(APPEND LEAN_EXTRA_OPTS " -Dbackward.do.legacy=false")
 # option used by the CI to fail on warnings
 option(WFAIL "Fail build if warnings are emitted by Lean" ON)
 if(WFAIL MATCHES "ON")
-  string(APPEND LAKE_EXTRA_ARGS " --wfail")
+  string(APPEND LEAN_EXTRA_LAKE_OPTS " --wfail")
   string(APPEND LEAN_EXTRA_MAKE_OPTS " -DwarningAsError=true")
 endif()
 

src/Init/Data/Array/QSort/Basic.lean

@@ -33,6 +33,7 @@ if necessary so that the middle (pivot) element is at index `hi`.
 We then iterate from `k = lo` to `k = hi`, with a pointer `i` starting at `lo`, and
 swapping each element which is less than the pivot to position `i`, and then incrementing `i`.
 -/
+@[inline]
 def qpartition {n} (as : Vector α n) (lt : α → α → Bool) (lo hi : Nat) (w : lo ≤ hi := by omega)
     (hlo : lo < n := by omega) (hhi : hi < n := by omega) : {m : Nat // lo ≤ m ∧ m ≤ hi} × Vector α n :=
   let mid := (lo + hi) / 2
@@ -44,7 +45,7 @@ def qpartition {n} (as : Vector α n) (lt : α → α → Bool) (lo hi : Nat) (w
   -- elements in `[i, k)` are greater than or equal to `pivot`,
   -- elements in `[k, hi)` are unexamined,
   -- while `as[hi]` is (by definition) the pivot.
-  let rec loop (as : Vector α n) (i k : Nat)
+  let rec @[specialize] loop (as : Vector α n) (i k : Nat)
       (ilo : lo ≤ i := by omega) (ik : i ≤ k := by omega) (w : k ≤ hi := by omega) :=
     if h : k < hi then
       if lt as[k] pivot then

src/Init/Data/Nat/Basic.lean

@@ -59,9 +59,9 @@ Examples:
 * `Nat.repeat f 3 a = f <| f <| f <| a`
 * `Nat.repeat (· ++ "!") 4 "Hello" = "Hello!!!!"`
 -/
-@[specialize, expose] def repeat {α : Type u} (f : α → α) : (n : Nat) → (a : α) → α
+@[specialize, expose] def «repeat» {α : Type u} (f : α → α) : (n : Nat) → (a : α) → α
   | 0,      a => a
-  | succ n, a => f (repeat f n a)
+  | succ n, a => f («repeat» f n a)
 
 /--
 Applies a function to a starting value the specified number of times.
@@ -1221,9 +1221,9 @@ theorem not_lt_eq (a b : Nat) : (¬ (a < b)) = (b ≤ a) :=
 theorem not_gt_eq (a b : Nat) : (¬ (a > b)) = (a ≤ b) :=
   not_lt_eq b a
 
-@[csimp] theorem repeat_eq_repeatTR : @repeat = @repeatTR :=
+@[csimp] theorem repeat_eq_repeatTR : @«repeat» = @repeatTR :=
   funext fun α => funext fun f => funext fun n => funext fun init =>
-  let rec go : ∀ m n, repeatTR.loop f m (repeat f n init) = repeat f (m + n) init
+  let rec go : ∀ m n, repeatTR.loop f m («repeat» f n init) = «repeat» f (m + n) init
     | 0,      n => by simp [repeatTR.loop]
     | succ m, n => by rw [repeatTR.loop, succ_add]; exact go m (succ n)
   (go n 0).symm

src/Init/Data/Order/LemmasExtra.lean

@@ -87,7 +87,7 @@ public theorem IsLinearOrder.of_ord {α : Type u} [LE α] [Ord α] [LawfulOrderO
 /--
 This lemma derives a `LawfulOrderLT α` instance from a property involving an `Ord α` instance.
 -/
-public instance LawfulOrderLT.of_ord (α : Type u) [Ord α] [LT α] [LE α] [LawfulOrderOrd α]
+public theorem LawfulOrderLT.of_ord (α : Type u) [Ord α] [LT α] [LE α] [LawfulOrderOrd α]
     (lt_iff_compare_eq_lt : ∀ a b : α, a < b ↔ compare a b = .lt) :
     LawfulOrderLT α where
   lt_iff a b := by
@@ -96,7 +96,7 @@ public instance LawfulOrderLT.of_ord (α : Type u) [Ord α] [LT α] [LE α] [Law
 /--
 This lemma derives a `LawfulOrderBEq α` instance from a property involving an `Ord α` instance.
 -/
-public instance LawfulOrderBEq.of_ord (α : Type u) [Ord α] [BEq α] [LE α] [LawfulOrderOrd α]
+public theorem LawfulOrderBEq.of_ord (α : Type u) [Ord α] [BEq α] [LE α] [LawfulOrderOrd α]
     (beq_iff_compare_eq_eq : ∀ a b : α, a == b ↔ compare a b = .eq) :
     LawfulOrderBEq α where
   beq_iff_le_and_ge := by
@@ -105,7 +105,7 @@ public instance LawfulOrderBEq.of_ord (α : Type u) [Ord α] [BEq α] [LE α] [L
 /--
 This lemma derives a `LawfulOrderInf α` instance from a property involving an `Ord α` instance.
 -/
-public instance LawfulOrderInf.of_ord (α : Type u) [Ord α] [Min α] [LE α] [LawfulOrderOrd α]
+public theorem LawfulOrderInf.of_ord (α : Type u) [Ord α] [Min α] [LE α] [LawfulOrderOrd α]
     (compare_min_isLE_iff : ∀ a b c : α,
         (compare a (min b c)).isLE ↔ (compare a b).isLE ∧ (compare a c).isLE) :
     LawfulOrderInf α where
@@ -114,7 +114,7 @@ public instance LawfulOrderInf.of_ord (α : Type u) [Ord α] [Min α] [LE α] [L
 /--
 This lemma derives a `LawfulOrderMin α` instance from a property involving an `Ord α` instance.
 -/
-public instance LawfulOrderMin.of_ord (α : Type u) [Ord α] [Min α] [LE α] [LawfulOrderOrd α]
+public theorem LawfulOrderMin.of_ord (α : Type u) [Ord α] [Min α] [LE α] [LawfulOrderOrd α]
     (compare_min_isLE_iff : ∀ a b c : α,
         (compare a (min b c)).isLE ↔ (compare a b).isLE ∧ (compare a c).isLE)
     (min_eq_or : ∀ a b : α, min a b = a ∨ min a b = b) :
@@ -125,7 +125,7 @@ public instance LawfulOrderMin.of_ord (α : Type u) [Ord α] [Min α] [LE α] [L
 /--
 This lemma derives a `LawfulOrderSup α` instance from a property involving an `Ord α` instance.
 -/
-public instance LawfulOrderSup.of_ord (α : Type u) [Ord α] [Max α] [LE α] [LawfulOrderOrd α]
+public theorem LawfulOrderSup.of_ord (α : Type u) [Ord α] [Max α] [LE α] [LawfulOrderOrd α]
     (compare_max_isLE_iff : ∀ a b c : α,
         (compare (max a b) c).isLE ↔ (compare a c).isLE ∧ (compare b c).isLE) :
     LawfulOrderSup α where
@@ -134,7 +134,7 @@ public instance LawfulOrderSup.of_ord (α : Type u) [Ord α] [Max α] [LE α] [L
 /--
 This lemma derives a `LawfulOrderMax α` instance from a property involving an `Ord α` instance.
 -/
-public instance LawfulOrderMax.of_ord (α : Type u) [Ord α] [Max α] [LE α] [LawfulOrderOrd α]
+public theorem LawfulOrderMax.of_ord (α : Type u) [Ord α] [Max α] [LE α] [LawfulOrderOrd α]
     (compare_max_isLE_iff : ∀ a b c : α,
         (compare (max a b) c).isLE ↔ (compare a c).isLE ∧ (compare b c).isLE)
     (max_eq_or : ∀ a b : α, max a b = a ∨ max a b = b) :

src/Init/Grind/Order.lean

@@ -75,6 +75,9 @@ theorem nat_eq (a b : Nat) (x y : Int) : NatCast.natCast a = x → NatCast.natCa
 theorem of_nat_eq (a b : Nat) (x y : Int) : NatCast.natCast a = x → NatCast.natCast b = y → a = b → x = y := by
   intro _ _; subst x y; intro; simp [*]
 
+theorem of_natCast_eq {α : Type u} [NatCast α] (a b : Nat) (x y : α) : NatCast.natCast a = x → NatCast.natCast b = y → a = b → x = y := by
+  intro h₁ h₂ h; subst h; exact h₁.symm.trans h₂
+
 theorem le_of_not_le {α} [LE α] [Std.IsLinearPreorder α]
     {a b : α} : ¬ a ≤ b → b ≤ a := by
   intro h

src/Init/While.lean

@@ -10,13 +10,14 @@ public import Init.Core
 
 public section
 
-/-!
-# Notation for `while` and `repeat` loops.
--/
-
 namespace Lean
 
-/-! # `repeat` and `while` notation -/
+/-!
+# `while` and `repeat` loop support
+
+The parsers for `repeat`, `while`, and `repeat ... until` are
+`@[builtin_doElem_parser]` definitions in `Lean.Parser.Do`.
+-/
 
 inductive Loop where
   | mk
@@ -32,24 +33,23 @@ partial def Loop.forIn {β : Type u} {m : Type u → Type v} [Monad m] (_ : Loop
 instance [Monad m] : ForIn m Loop Unit where
   forIn := Loop.forIn
 
-syntax "repeat " doSeq : doElem
+-- The canonical parsers for `repeat`/`while`/`repeat ... until` live in `Lean.Parser.Do`
+-- as `@[builtin_doElem_parser]` definitions. We register the expansion macros here so
+-- they are available to `prelude` files in `Init`, which do not import `Lean.Elab`.
 
 macro_rules
-  | `(doElem| repeat $seq) => `(doElem| for _ in Loop.mk do $seq)
-
-syntax "while " ident " : " termBeforeDo " do " doSeq : doElem
+  | `(doElem| repeat%$tk $seq) => `(doElem| for%$tk _ in Loop.mk do $seq)
 
 macro_rules
-  | `(doElem| while $h : $cond do $seq) => `(doElem| repeat if $h:ident : $cond then $seq else break)
-
-syntax "while " termBeforeDo " do " doSeq : doElem
+  | `(doElem| while%$tk $h : $cond do $seq) =>
+    `(doElem| repeat%$tk if $h:ident : $cond then $seq else break)
 
 macro_rules
-  | `(doElem| while $cond do $seq) => `(doElem| repeat if $cond then $seq else break)
-
-syntax "repeat " doSeq ppDedent(ppLine) "until " term : doElem
+  | `(doElem| while%$tk $cond do $seq) =>
+    `(doElem| repeat%$tk if $cond then $seq else break)
 
 macro_rules
-  | `(doElem| repeat $seq until $cond) => `(doElem| repeat do $seq:doSeq; if $cond then break)
+  | `(doElem| repeat%$tk $seq until $cond) =>
+    `(doElem| repeat%$tk do $seq:doSeq; if $cond then break)
 
 end Lean

src/Lean/Compiler/LCNF/EmitC.lean

@@ -207,7 +207,7 @@ def emitLns [EmitToString α] (as : List α) : EmitM Unit :=
   emitLn "}"
   return ret
 
-def toHexDigit (c : Nat) : String :=
+def toDigit (c : Nat) : String :=
   String.singleton c.digitChar
 
 def quoteString (s : String) : String :=
@@ -221,7 +221,11 @@ def quoteString (s : String) : String :=
       else if c == '\"' then "\\\""
       else if c == '?' then "\\?" -- avoid trigraphs
       else if c.toNat <= 31 then
-        "\\x" ++ toHexDigit (c.toNat / 16) ++ toHexDigit (c.toNat % 16)
+        -- Use octal escapes instead of hex escapes because C hex escapes are
+        -- greedy: "\x01abc" would be parsed as the single escape \x01abc rather
+        -- than \x01 followed by "abc".  Octal escapes consume at most 3 digits.
+        let n := c.toNat
+        "\\" ++ toDigit (n / 64) ++ toDigit ((n / 8) % 8) ++ toDigit (n % 8)
       -- TODO(Leo): we should use `\unnnn` for escaping unicode characters.
       else String.singleton c)
     q;

src/Lean/Compiler/LCNF/ExpandResetReuse.lean

@@ -90,6 +90,22 @@ partial def eraseProjIncFor (nFields : Nat) (targetId : FVarId) (ds : Array (Cod
         | break
       if !(w == z && targetId == x) then
         break
+      if mask[i]!.isSome then
+        /-
+        Suppose we encounter a situation like
+        ```
+        let x.1 := proj[0] y
+        inc x.1
+        let x.2 := proj[0] y
+        inc x.2
+        ```
+        The `inc x.2` will already have been removed. If we don't perform this check we will also
+        remove `inc x.1` and have effectively removed two refcounts while only one was legal.
+        -/
+        keep := keep.push d
+        keep := keep.push d'
+        ds := ds.pop.pop
+        continue
       /-
       Found
       ```

src/Lean/Elab/BuiltinDo.lean

@@ -15,3 +15,4 @@ public import Lean.Elab.BuiltinDo.Jump
 public import Lean.Elab.BuiltinDo.Misc
 public import Lean.Elab.BuiltinDo.For
 public import Lean.Elab.BuiltinDo.TryCatch
+public import Lean.Elab.BuiltinDo.Repeat

src/Lean/Elab/BuiltinDo/Basic.lean

@@ -21,7 +21,8 @@ def elabDoIdDecl (x : Ident) (xType? : Option Term) (rhs : TSyntax `doElem) (k :
   let xType ← Term.elabType (xType?.getD (mkHole x))
   let lctx ← getLCtx
   let ctx ← read
-  elabDoElem rhs <| .mk (kind := kind) x.getId xType do
+  let ref ← getRef -- store the surrounding reference for error messages in `k`
+  elabDoElem rhs <| .mk (kind := kind) x.getId xType do withRef ref do
     withLCtxKeepingMutVarDefs lctx ctx x.getId do
       Term.addLocalVarInfo x (← getFVarFromUserName x.getId)
       k

src/Lean/Elab/BuiltinDo/For.lean

@@ -23,7 +23,7 @@ open Lean.Meta
   | `(doFor| for $[$_ : ]? $_:ident in $_ do $_) =>
     -- This is the target form of the expander, handled by `elabDoFor` below.
     Macro.throwUnsupported
-  | `(doFor| for $decls:doForDecl,* do $body) =>
+  | `(doFor| for%$tk $decls:doForDecl,* do $body) =>
     let decls := decls.getElems
     let `(doForDecl| $[$h? : ]? $pattern in $xs) := decls[0]! | Macro.throwUnsupported
     let mut doElems := #[]
@@ -74,12 +74,13 @@ open Lean.Meta
           | some ($y, s') =>
             $s:ident := s'
             do $body)
-    doElems := doElems.push (← `(doSeqItem| for $[$h? : ]? $x:ident in $xs do $body))
+    doElems := doElems.push (← `(doSeqItem| for%$tk $[$h? : ]? $x:ident in $xs do $body))
     `(doElem| do $doElems*)
   | _ => Macro.throwUnsupported
 
 @[builtin_doElem_elab Lean.Parser.Term.doFor] def elabDoFor : DoElab := fun stx dec => do
-  let `(doFor| for $[$h? : ]? $x:ident in $xs do $body) := stx | throwUnsupportedSyntax
+  let `(doFor| for%$tk $[$h? : ]? $x:ident in $xs do $body) := stx | throwUnsupportedSyntax
+  let dec ← dec.ensureUnitAt tk
   checkMutVarsForShadowing #[x]
   let uα ← mkFreshLevelMVar
   let uρ ← mkFreshLevelMVar
@@ -124,9 +125,6 @@ open Lean.Meta
       defs := defs.push (mkConst ``Unit.unit)
     return defs
 
-  unless ← isDefEq dec.resultType (← mkPUnit) do
-    logError m!"Type mismatch. `for` loops have result type {← mkPUnit}, but the rest of the `do` sequence expected {dec.resultType}."
-
   let (preS, σ) ← mkProdMkN (← useLoopMutVars none) mi.u
 
   let (app, p?) ← match h? with

src/Lean/Elab/BuiltinDo/If.lean

@@ -17,6 +17,7 @@ namespace Lean.Elab.Do
 open Lean.Parser.Term
 open Lean.Meta
 
+open InternalSyntax in
 /--
 If the given syntax is a `doIf`, return an equivalent `doIf` that has an `else` but no `else if`s or
 `if let`s.
@@ -25,8 +26,8 @@ If the given syntax is a `doIf`, return an equivalent `doIf` that has an `else`
   match stx with
   | `(doElem|if $_:doIfProp then $_ else $_) =>
     Macro.throwUnsupported
-  | `(doElem|if $cond:doIfCond then $t $[else if $conds:doIfCond then $ts]* $[else $e?]?) => do
-    let mut e : Syntax ← e?.getDM `(doSeq|pure PUnit.unit)
+  | `(doElem|if%$tk $cond:doIfCond then $t $[else if%$tks $conds:doIfCond then $ts]* $[else $e?]?) => do
+    let mut e : Syntax ← e?.getDM `(doSeq| skip%$tk)
     let mut eIsSeq := true
     for (cond, t) in Array.zip (conds.reverse.push cond) (ts.reverse.push t) do
       e ← if eIsSeq then pure e else `(doSeq|$(⟨e⟩):doElem)

src/Lean/Elab/BuiltinDo/Let.lean

@@ -88,17 +88,18 @@ private def checkLetConfigInDo (config : Term.LetConfig) : DoElabM Unit := do
     throwError "`+generalize` is not supported in `do` blocks"
 
 partial def elabDoLetOrReassign (config : Term.LetConfig) (letOrReassign : LetOrReassign) (decl : TSyntax ``letDecl)
-    (dec : DoElemCont) : DoElabM Expr := do
+    (tk : Syntax) (dec : DoElemCont) : DoElabM Expr := do
   checkLetConfigInDo config
   let vars ← getLetDeclVars decl
   letOrReassign.checkMutVars vars
+  let dec ← dec.ensureUnitAt tk
   -- Some decl preprocessing on the patterns and expected types:
   let decl ← pushTypeIntoReassignment letOrReassign decl
   let mγ ← mkMonadicType (← read).doBlockResultType
   match decl with
   | `(letDecl| $decl:letEqnsDecl) =>
     let declNew ← `(letDecl| $(⟨← liftMacroM <| Term.expandLetEqnsDecl decl⟩):letIdDecl)
-    return ← Term.withMacroExpansion decl declNew <| elabDoLetOrReassign config letOrReassign declNew dec
+    return ← Term.withMacroExpansion decl declNew <| elabDoLetOrReassign config letOrReassign declNew tk dec
   | `(letDecl| $pattern:term $[: $xType?]? := $rhs) =>
     let rhs ← match xType? with | some xType => `(($rhs : $xType)) | none => pure rhs
     let contElab : DoElabM Expr := elabWithReassignments letOrReassign vars dec.continueWithUnit
@@ -162,10 +163,11 @@ partial def elabDoLetOrReassign (config : Term.LetConfig) (letOrReassign : LetOr
             mkLetFVars #[x, h'] body (usedLetOnly := config.usedOnly) (generalizeNondepLet := false)
   | _ => throwUnsupportedSyntax
 
-def elabDoArrow (letOrReassign : LetOrReassign) (stx : TSyntax [``doIdDecl, ``doPatDecl]) (dec : DoElemCont) : DoElabM Expr := do
+def elabDoArrow (letOrReassign : LetOrReassign) (stx : TSyntax [``doIdDecl, ``doPatDecl]) (tk : Syntax) (dec : DoElemCont) : DoElabM Expr := do
   match stx with
   | `(doIdDecl| $x:ident $[: $xType?]? ← $rhs) =>
     letOrReassign.checkMutVars #[x]
+    let dec ← dec.ensureUnitAt tk
     -- For plain variable reassignment, we know the expected type of the reassigned variable and
     -- propagate it eagerly via type ascription if the user hasn't provided one themselves:
     let xType? ← match letOrReassign, xType? with
@@ -177,6 +179,7 @@ def elabDoArrow (letOrReassign : LetOrReassign) (stx : TSyntax [``doIdDecl, ``do
       (kind := dec.kind)
   | `(doPatDecl| _%$pattern $[: $patType?]? ← $rhs) =>
     let x := mkIdentFrom pattern (← mkFreshUserName `__x)
+    let dec ← dec.ensureUnitAt tk
     elabDoIdDecl x patType? rhs dec.continueWithUnit (kind := dec.kind)
   | `(doPatDecl| $pattern:term $[: $patType?]? ← $rhs $[| $otherwise? $(rest?)?]?) =>
     let rest? := rest?.join
@@ -205,17 +208,18 @@ private def getLetConfigAndCheckMut (letConfigStx : TSyntax ``Parser.Term.letCon
   Term.mkLetConfig letConfigStx initConfig
 
 @[builtin_doElem_elab Lean.Parser.Term.doLet] def elabDoLet : DoElab := fun stx dec => do
-  let `(doLet| let $[mut%$mutTk?]? $config:letConfig $decl:letDecl) := stx | throwUnsupportedSyntax
+  let `(doLet| let%$tk $[mut%$mutTk?]? $config:letConfig $decl:letDecl) := stx | throwUnsupportedSyntax
   let config ← getLetConfigAndCheckMut config mutTk?
-  elabDoLetOrReassign config (.let mutTk?) decl dec
+  elabDoLetOrReassign config (.let mutTk?) decl tk dec
 
 @[builtin_doElem_elab Lean.Parser.Term.doHave] def elabDoHave : DoElab := fun stx dec => do
-  let `(doHave| have $config:letConfig $decl:letDecl) := stx | throwUnsupportedSyntax
+  let `(doHave| have%$tk $config:letConfig $decl:letDecl) := stx | throwUnsupportedSyntax
   let config ← Term.mkLetConfig config { nondep := true }
-  elabDoLetOrReassign config .have decl dec
+  elabDoLetOrReassign config .have decl tk dec
 
 @[builtin_doElem_elab Lean.Parser.Term.doLetRec] def elabDoLetRec : DoElab := fun stx dec => do
-  let `(doLetRec| let rec $decls:letRecDecls) := stx | throwUnsupportedSyntax
+  let `(doLetRec| let%$tk rec $decls:letRecDecls) := stx | throwUnsupportedSyntax
+  let dec ← dec.ensureUnitAt tk
   let vars ← getLetRecDeclsVars decls
   let mγ ← mkMonadicType (← read).doBlockResultType
   doElabToSyntax m!"let rec body of group {vars}" dec.continueWithUnit fun body => do
@@ -227,13 +231,13 @@ private def getLetConfigAndCheckMut (letConfigStx : TSyntax ``Parser.Term.letCon
 @[builtin_doElem_elab Lean.Parser.Term.doReassign] def elabDoReassign : DoElab := fun stx dec => do
   -- def doReassign := letIdDeclNoBinders <|> letPatDecl
   match stx with
-  | `(doReassign| $x:ident $[: $xType?]? := $rhs) =>
+  | `(doReassign| $x:ident $[: $xType?]? :=%$tk $rhs) =>
     let decl : TSyntax ``letIdDecl ← `(letIdDecl| $x:ident $[: $xType?]? := $rhs)
     let decl : TSyntax ``letDecl := ⟨mkNode ``letDecl #[decl]⟩
-    elabDoLetOrReassign {} .reassign decl dec
+    elabDoLetOrReassign {} .reassign decl tk dec
   | `(doReassign| $decl:letPatDecl) =>
     let decl : TSyntax ``letDecl := ⟨mkNode ``letDecl #[decl]⟩
-    elabDoLetOrReassign {} .reassign decl dec
+    elabDoLetOrReassign {} .reassign decl decl dec
   | _ => throwUnsupportedSyntax
 
 @[builtin_doElem_elab Lean.Parser.Term.doLetElse] def elabDoLetElse : DoElab := fun stx dec => do
@@ -255,17 +259,17 @@ private def getLetConfigAndCheckMut (letConfigStx : TSyntax ``Parser.Term.letCon
     elabDoElem (← `(doElem| match $rhs:term with | $pattern => $body:doSeqIndent | _ => $otherwise:doSeqIndent)) dec
 
 @[builtin_doElem_elab Lean.Parser.Term.doLetArrow] def elabDoLetArrow : DoElab := fun stx dec => do
-  let `(doLetArrow| let $[mut%$mutTk?]? $cfg:letConfig $decl) := stx | throwUnsupportedSyntax
+  let `(doLetArrow| let%$tk $[mut%$mutTk?]? $cfg:letConfig $decl) := stx | throwUnsupportedSyntax
   let config ← getLetConfigAndCheckMut cfg mutTk?
   checkLetConfigInDo config
   if config.nondep || config.usedOnly || config.zeta || config.eq?.isSome then
     throwErrorAt cfg "configuration options are not supported with `←`"
-  elabDoArrow (.let mutTk?) decl dec
+  elabDoArrow (.let mutTk?) decl tk dec
 
 @[builtin_doElem_elab Lean.Parser.Term.doReassignArrow] def elabDoReassignArrow : DoElab := fun stx dec => do
   match stx with
   | `(doReassignArrow| $decl:doIdDecl) =>
-    elabDoArrow .reassign decl dec
+    elabDoArrow .reassign decl decl dec
   | `(doReassignArrow| $decl:doPatDecl) =>
-    elabDoArrow .reassign decl dec
+    elabDoArrow .reassign decl decl dec
   | _ => throwUnsupportedSyntax

src/Lean/Elab/BuiltinDo/Misc.lean

@@ -16,6 +16,12 @@ namespace Lean.Elab.Do
 open Lean.Parser.Term
 open Lean.Meta
 
+open InternalSyntax in
+@[builtin_doElem_elab Lean.Parser.Term.InternalSyntax.doSkip] def elabDoSkip : DoElab := fun stx dec => do
+  let `(doSkip| skip%$tk) := stx | throwUnsupportedSyntax
+  let dec ← dec.ensureUnitAt tk
+  dec.continueWithUnit
+
 @[builtin_doElem_elab Lean.Parser.Term.doExpr] def elabDoExpr : DoElab := fun stx dec => do
   let `(doExpr| $e:term) := stx | throwUnsupportedSyntax
   let mα ← mkMonadicType dec.resultType
@@ -26,24 +32,28 @@ open Lean.Meta
   let `(doNested| do $doSeq) := stx | throwUnsupportedSyntax
   elabDoSeq ⟨doSeq.raw⟩ dec
 
+open InternalSyntax in
 @[builtin_doElem_elab Lean.Parser.Term.doUnless] def elabDoUnless : DoElab := fun stx dec => do
-  let `(doUnless| unless $cond do $body) := stx | throwUnsupportedSyntax
-  elabDoElem (← `(doElem| if $cond then pure PUnit.unit else $body)) dec
+  let `(doUnless| unless%$tk $cond do $body) := stx | throwUnsupportedSyntax
+  elabDoElem (← `(doElem| if $cond then skip%$tk else $body)) dec
 
 @[builtin_doElem_elab Lean.Parser.Term.doDbgTrace] def elabDoDbgTrace : DoElab := fun stx dec => do
-  let `(doDbgTrace| dbg_trace $msg:term) := stx | throwUnsupportedSyntax
+  let `(doDbgTrace| dbg_trace%$tk $msg:term) := stx | throwUnsupportedSyntax
   let mγ ← mkMonadicType (← read).doBlockResultType
+  let dec ← dec.ensureUnitAt tk
   doElabToSyntax "dbg_trace body" dec.continueWithUnit fun body => do
   Term.elabTerm (← `(dbg_trace $msg; $body)) mγ
 
 @[builtin_doElem_elab Lean.Parser.Term.doAssert] def elabDoAssert : DoElab := fun stx dec => do
-  let `(doAssert| assert! $cond) := stx | throwUnsupportedSyntax
+  let `(doAssert| assert!%$tk $cond) := stx | throwUnsupportedSyntax
   let mγ ← mkMonadicType (← read).doBlockResultType
+  let dec ← dec.ensureUnitAt tk
   doElabToSyntax "assert! body" dec.continueWithUnit fun body => do
   Term.elabTerm (← `(assert! $cond; $body)) mγ
 
 @[builtin_doElem_elab Lean.Parser.Term.doDebugAssert] def elabDoDebugAssert : DoElab := fun stx dec => do
-  let `(doDebugAssert| debug_assert! $cond) := stx | throwUnsupportedSyntax
+  let `(doDebugAssert| debug_assert!%$tk $cond) := stx | throwUnsupportedSyntax
   let mγ ← mkMonadicType (← read).doBlockResultType
+  let dec ← dec.ensureUnitAt tk
   doElabToSyntax "debug_assert! body" dec.continueWithUnit fun body => do
   Term.elabTerm (← `(debug_assert! $cond; $body)) mγ

src/Lean/Elab/BuiltinDo/Repeat.lean

@@ -0,0 +1,44 @@
+/-
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Graf
+-/
+module
+
+prelude
+public import Lean.Elab.BuiltinDo.Basic
+meta import Lean.Parser.Do
+import Lean.Elab.BuiltinDo.For
+
+public section
+
+namespace Lean.Elab.Do
+
+open Lean.Parser.Term
+
+/--
+Builtin do-element elaborator for `repeat` (syntax kind `Lean.Parser.Term.doRepeat`).
+
+Expands to `for _ in Loop.mk do ...`. A follow-up change will extend this
+elaborator to choose between `Loop.mk` and a well-founded `Repeat.mk` based on a
+configuration option.
+-/
+@[builtin_doElem_elab Lean.Parser.Term.doRepeat] def elabDoRepeat : DoElab := fun stx dec => do
+  let `(doElem| repeat%$tk $seq) := stx | throwUnsupportedSyntax
+  let expanded ← `(doElem| for%$tk _ in Loop.mk do $seq)
+  Term.withMacroExpansion stx expanded <|
+    withRef expanded <| elabDoElem ⟨expanded⟩ dec
+
+@[builtin_macro Lean.Parser.Term.doWhileH] def expandDoWhileH : Macro
+  | `(doElem| while%$tk $h : $cond do $seq) => `(doElem| repeat%$tk if $h:ident : $cond then $seq else break)
+  | _ => Macro.throwUnsupported
+
+@[builtin_macro Lean.Parser.Term.doWhile] def expandDoWhile : Macro
+  | `(doElem| while%$tk $cond do $seq) => `(doElem| repeat%$tk if $cond then $seq else break)
+  | _ => Macro.throwUnsupported
+
+@[builtin_macro Lean.Parser.Term.doRepeatUntil] def expandDoRepeatUntil : Macro
+  | `(doElem| repeat%$tk $seq until $cond) => `(doElem| repeat%$tk do $seq:doSeq; if $cond then break)
+  | _ => Macro.throwUnsupported
+
+end Lean.Elab.Do

src/Lean/Elab/Deriving/Basic.lean

@@ -220,7 +220,7 @@ def processDefDeriving (view : DerivingClassView) (decl : Expr) (isNoncomputable
             instName ← liftMacroM <| mkUnusedBaseName instName
             if isPrivateName declName then
               instName := mkPrivateName env instName
-            let isMeta := (← read).declName?.any (isMarkedMeta (← getEnv))
+            let isMeta := (← read).isMetaSection || isMarkedMeta (← getEnv) declName
             let inst ← if backward.inferInstanceAs.wrap.get (← getOptions) then
               withDeclNameForAuxNaming instName <| withNewMCtxDepth <|
                 wrapInstance result.instVal result.instType
@@ -255,11 +255,12 @@ def processDefDeriving (view : DerivingClassView) (decl : Expr) (isNoncomputable
             logInfoAt cmdRef m!"Try this: {newText}"
         throwError "failed to derive instance because it depends on \
           `{.ofConstName noncompRef}`, which is noncomputable"
+    let isMeta := (← read).isMetaSection || isMarkedMeta (← getEnv) declName
     if isNoncomputable || (← read).isNoncomputableSection then
       addDecl <| Declaration.defnDecl decl
       modifyEnv (addNoncomputable · instName)
     else
-      addAndCompile <| Declaration.defnDecl decl
+      addAndCompile (Declaration.defnDecl decl) (markMeta := isMeta)
   trace[Elab.Deriving] "Derived instance `{.ofConstName instName}`"
   -- For Prop-typed instances (theorems), skip `implicit_reducible` since reducibility hints are
   -- irrelevant for theorems. This matches the behavior of the handwritten `instance` command

src/Lean/Elab/Do/Basic.lean

@@ -374,14 +374,60 @@ def withLCtxKeepingMutVarDefs (oldLCtx : LocalContext) (oldCtx : Context) (resul
     mutVarDefs := oldMutVarDefs
   }) k
 
+def mkMonadicResultTypeMismatchError (contType : Expr) (elementType : Expr) : MessageData :=
+  m!"Type mismatch. The `do` element has monadic result type{indentExpr elementType}\n\
+    but the rest of the `do` block has monadic result type{indentExpr contType}"
+
+/--
+Given a continuation `dec`, a reference `ref`, and an element result type `elementType`, returns a
+continuation derived from `dec` with result type `elementType`.
+If `dec` already has result type `elementType`, simply returns `dec`.
+Otherwise, an error is logged and a new continuation is returned that calls `dec` with `sorry` as a
+result. The error is reported at `ref`.
+-/
+def DoElemCont.ensureHasTypeAt (dec : DoElemCont) (ref : Syntax) (elementType : Expr) : DoElabM DoElemCont := do
+  if ← isDefEqGuarded dec.resultType elementType then
+    return dec
+  let errMessage := mkMonadicResultTypeMismatchError dec.resultType elementType
+  unless (← readThe Term.Context).errToSorry do
+    throwErrorAt ref errMessage
+  logErrorAt ref errMessage
+  return {
+    resultName := ← mkFreshUserName `__r
+    resultType := elementType
+    k := do
+      mapLetDecl dec.resultName dec.resultType (← mkSorry dec.resultType true)
+          (nondep := true) (kind := .implDetail) fun _ => dec.k
+    kind := dec.kind
+  }
+
+/--
+Given a continuation `dec` and a reference `ref`, returns a continuation derived from `dec` with result type `PUnit`.
+If `dec` already has result type `PUnit`, simply returns `dec`. Otherwise, an error is logged and a
+new continuation is returned that calls `dec` with `sorry` as a result. The error is reported at `ref`.
+-/
+def DoElemCont.ensureUnitAt (dec : DoElemCont) (ref : Syntax) : DoElabM DoElemCont := do
+  dec.ensureHasTypeAt ref (← mkPUnit)
+
+/--
+Given a continuation `dec`, returns a continuation derived from `dec` with result type `PUnit`.
+If `dec` already has result type `PUnit`, simply returns `dec`. Otherwise, an error is logged and a
+new continuation is returned that calls `dec` with `sorry` as a result.
+-/
+def DoElemCont.ensureUnit (dec : DoElemCont) : DoElabM DoElemCont := do
+  dec.ensureUnitAt (← getRef)
+
 /--
 Return `$e >>= fun ($dec.resultName : $dec.resultType) => $(← dec.k)`, cancelling
 the bind if `$(← dec.k)` is `pure $dec.resultName` or `e` is some `pure` computation.
 -/
 def DoElemCont.mkBindUnlessPure (dec : DoElemCont) (e : Expr) : DoElabM Expr := do
+  -- let eResultTy ← mkFreshResultType
+  -- let e ← Term.ensureHasType (← mkMonadicType eResultTy) e
+  -- let dec ← dec.ensureHasType eResultTy
   let x := dec.resultName
-  let eResultTy := dec.resultType
   let k := dec.k
+  let eResultTy := dec.resultType
   -- The .ofBinderName below is mainly to interpret `__do_lift` binders as implementation details.
   let declKind := .ofBinderName x
   let kResultTy ← mkFreshResultType `kResultTy
@@ -421,9 +467,8 @@ Return `let $k.resultName : PUnit := PUnit.unit; $(← k.k)`, ensuring that the
 is `PUnit` and then immediately zeta-reduce the `let`.
 -/
 def DoElemCont.continueWithUnit (dec : DoElemCont) : DoElabM Expr := do
-  let unit ← mkPUnitUnit
-  discard <| Term.ensureHasType dec.resultType unit
-  mapLetDeclZeta dec.resultName (← mkPUnit) unit (nondep := true) (kind := .ofBinderName dec.resultName) fun _ =>
+  let dec ← dec.ensureUnit
+  mapLetDeclZeta dec.resultName (← mkPUnit) (← mkPUnitUnit) (nondep := true) (kind := .ofBinderName dec.resultName) fun _ =>
     dec.k
 
 /-- Elaborate the `DoElemCont` with the `deadCode` flag set to `deadSyntactically` to emit warnings. -/
@@ -604,6 +649,7 @@ def enterFinally (resultType : Expr) (k : DoElabM Expr) : DoElabM Expr := do
 /-- Extracts `MonadInfo` and monadic result type `α` from the expected type of a `do` block `m α`. -/
 private partial def extractMonadInfo (expectedType? : Option Expr) : Term.TermElabM (MonadInfo × Expr) := do
   let some expectedType := expectedType? | mkUnknownMonadResult
+  let expectedType ← instantiateMVars expectedType
   let extractStep? (type : Expr) : Term.TermElabM (Option (MonadInfo × Expr)) := do
     let .app m resultType := type.consumeMData | return none
     unless ← isType resultType do return none

src/Lean/Elab/Do/InferControlInfo.lean

@@ -79,6 +79,7 @@ builtin_initialize controlInfoElemAttribute : KeyedDeclsAttribute ControlInfoHan
 
 namespace InferControlInfo
 
+open InternalSyntax in
 mutual
 
 partial def ofElem (stx : TSyntax `doElem) : TermElabM ControlInfo := do
@@ -128,6 +129,7 @@ partial def ofElem (stx : TSyntax `doElem) : TermElabM ControlInfo := do
     return thenInfo.alternative info
   | `(doElem| unless $_ do $elseSeq) =>
     ControlInfo.alternative {} <$> ofSeq elseSeq
+  -- For/Repeat
   | `(doElem| for $[$[$_ :]? $_ in $_],* do $bodySeq) =>
     let info ← ofSeq bodySeq
     return { info with  -- keep only reassigns and earlyReturn
@@ -135,6 +137,13 @@ partial def ofElem (stx : TSyntax `doElem) : TermElabM ControlInfo := do
       continues := false,
       breaks := false
     }
+  | `(doRepeat| repeat $bodySeq) =>
+    let info ← ofSeq bodySeq
+    return { info with
+      numRegularExits := if info.breaks then 1 else 0,
+      continues := false,
+      breaks := false
+    }
   -- Try
   | `(doElem| try $trySeq:doSeq $[$catches]* $[finally $finSeq?]?) =>
     let mut info ← ofSeq trySeq
@@ -152,6 +161,7 @@ partial def ofElem (stx : TSyntax `doElem) : TermElabM ControlInfo := do
     let finInfo ← ofOptionSeq finSeq?
     return info.sequence finInfo
   -- Misc
+  | `(doElem| skip) => return .pure
   | `(doElem| dbg_trace $_) => return .pure
   | `(doElem| assert! $_) => return .pure
   | `(doElem| debug_assert! $_) => return .pure

src/Lean/Elab/Do/Legacy.lean

@@ -1782,6 +1782,10 @@ mutual
             doIfToCode doElem doElems
           else if k == ``Parser.Term.doUnless then
             doUnlessToCode doElem doElems
+          else if k == ``Parser.Term.doRepeat then
+            let seq := doElem[1]
+            let expanded ← `(doElem| for _ in Loop.mk do $seq)
+            doSeqToCode (expanded :: doElems)
           else if k == ``Parser.Term.doFor then withFreshMacroScope do
             doForToCode doElem doElems
           else if k == ``Parser.Term.doMatch then
@@ -1815,6 +1819,13 @@ mutual
               return mkTerminalAction term
             else
               return mkSeq term (← doSeqToCode doElems)
+          else if k == ``Parser.Term.InternalSyntax.doSkip then
+            -- In the legacy elaborator, `skip` is treated as `pure PUnit.unit`.
+            let term ← withRef doElem `(pure PUnit.unit)
+            if doElems.isEmpty then
+              return mkTerminalAction term
+            else
+              return mkSeq term (← doSeqToCode doElems)
           else
             throwError "unexpected do-element of kind {doElem.getKind}:\n{doElem}"
 end

src/Lean/Elab/Idbg.lean

@@ -364,8 +364,9 @@ def elabIdbgTerm : TermElab := fun stx expectedType? => do
 
 @[builtin_doElem_elab Lean.Parser.Term.doIdbg]
 def elabDoIdbg : DoElab := fun stx dec => do
-  let `(Lean.Parser.Term.doIdbg| idbg $e) := stx | throwUnsupportedSyntax
+  let `(Lean.Parser.Term.doIdbg| idbg%$tk $e) := stx | throwUnsupportedSyntax
   let mγ ← mkMonadicType (← read).doBlockResultType
+  let dec ← dec.ensureUnitAt tk
   doElabToSyntax "idbg body" dec.continueWithUnit fun body => do
     elabIdbgCore (e := e) (body := body) (ref := stx) mγ
 

src/Lean/Elab/Inductive.lean

@@ -73,6 +73,8 @@ private def inductiveSyntaxToView (modifiers : Modifiers) (decl : Syntax) (isCoi
         throwError "Constructor cannot be `protected` because it is in a `private` inductive datatype"
       checkValidCtorModifier ctorModifiers
       let ctorName := ctor.getIdAt 3
+      if ctorName.hasMacroScopes && isCoinductive then
+        throwError "Coinductive predicates are not allowed inside of macro scopes"
       let ctorName := declName ++ ctorName
       let ctorName ← withRef ctor[3] <| applyVisibility ctorModifiers ctorName
       let (binders, type?) := expandOptDeclSig ctor[4]

src/Lean/Meta/ACLt.lean

@@ -175,6 +175,7 @@ where
     return !(← allChildrenLt a b)
 
   lpo (a b : Expr) : MetaM Bool := do
+    checkSystem "Lean.Meta.acLt"
     -- Case 1: `a < b` if for some child `b_i` of `b`, we have `b_i >= a`
     if (← someChildGe b a) then
       return true

src/Lean/Meta/DecLevel.lean

@@ -69,12 +69,16 @@ def decLevel (u : Level) : MetaM Level := do
 
 /-- This method is useful for inferring universe level parameters for function that take arguments such as `{α : Type u}`.
    Recall that `Type u` is `Sort (u+1)` in Lean. Thus, given `α`, we must infer its universe level,
-   and then decrement 1 to obtain `u`. -/
+   instantiate and normalize it, and then decrement 1 to obtain `u`. -/
 def getDecLevel (type : Expr) : MetaM Level := do
-  decLevel (← getLevel type)
+  let l ← getLevel type
+  let l ← normalizeLevel l
+  decLevel l
 
 def getDecLevel? (type : Expr) : MetaM (Option Level) := do
-  decLevel? (← getLevel type)
+  let l ← getLevel type
+  let l ← normalizeLevel l
+  decLevel? l
 
 builtin_initialize
   registerTraceClass `Meta.isLevelDefEq.step

src/Lean/Meta/Instances.lean

@@ -229,8 +229,33 @@ private partial def computeSynthOrder (inst : Expr) (projInfo? : Option Projecti
 
   return synthed
 
+def checkImpossibleInstance (c : Expr) : MetaM Unit := do
+  let cTy ← inferType c
+  forallTelescopeReducing cTy fun args ty => do
+    let argTys ← args.mapM inferType
+    let impossibleArgs ← args.zipIdx.filterMapM fun (arg, i) => do
+      let fv := arg.fvarId!
+      if (← fv.getDecl).binderInfo.isInstImplicit then return none
+      if ty.containsFVar fv then return none
+      if argTys[i+1:].any (·.containsFVar fv) then return none
+      return some m!"{arg} : {← inferType arg}"
+    if impossibleArgs.isEmpty then return
+    let impossibleArgs := MessageData.joinSep impossibleArgs.toList ", "
+    throwError m!"Instance {c} has arguments "
+      ++ impossibleArgs
+      ++ " that are impossible to infer. Those arguments are not instance-implicit and do not appear in another instance-implicit argument or the return type."
+
+def checkNonClassInstance (declName : Name) (c : Expr) : MetaM Unit := do
+  let type ← inferType c
+  forallTelescopeReducing type fun _ target => do
+    unless (← isClass? target).isSome do
+      unless target.isSorry do
+      throwError m!"instance `{declName}` target `{target}` is not a type class."
+
 def addInstance (declName : Name) (attrKind : AttributeKind) (prio : Nat) : MetaM Unit := do
   let c ← mkConstWithLevelParams declName
+  checkImpossibleInstance c
+  checkNonClassInstance declName c
   let keys ← mkInstanceKey c
   let status ← getReducibilityStatus declName
   unless status matches .reducible | .implicitReducible do

src/Lean/Meta/LevelDefEq.lean

@@ -38,7 +38,9 @@ and assigning `?m := max ?n v`
 private def solveSelfMax (mvarId : LMVarId) (v : Level) : MetaM Unit := do
   assert! v.isMax
   let n ← mkFreshLevelMVar
-  assignLevelMVar mvarId <| mkMaxArgsDiff mvarId v n
+  let v' := mkMaxArgsDiff mvarId v n
+  trace[Meta.isLevelDefEq.step] "solveSelfMax: {mkLevelMVar mvarId} := {v'}"
+  assignLevelMVar mvarId v'
 
 /--
 Returns true if `v` is `max u ?m` (or variant). That is, we solve `u =?= max u ?m` as `?m := u`.
@@ -53,6 +55,7 @@ private def tryApproxSelfMax (u v : Level) : MetaM Bool := do
 where
   solve (v' : Level) (mvarId : LMVarId) : MetaM Bool := do
     if u == v' then
+      trace[Meta.isLevelDefEq.step] "tryApproxSelfMax {mkLevelMVar mvarId} := {u}"
       assignLevelMVar mvarId u
       return true
     else
@@ -71,8 +74,14 @@ private def tryApproxMaxMax (u v : Level) : MetaM Bool := do
   | _, _ => return false
 where
   solve (u₁ u₂ v' : Level) (mvarId : LMVarId) : MetaM Bool := do
-    if u₁ == v' then assignLevelMVar mvarId u₂; return true
-    else if u₂ == v' then assignLevelMVar mvarId u₁; return true
+    if u₁ == v' then
+      trace[Meta.isLevelDefEq.step] "tryApproxMaxMax {mkLevelMVar mvarId} := {u₂}"
+      assignLevelMVar mvarId u₂
+      return true
+    else if u₂ == v' then
+      trace[Meta.isLevelDefEq.step] "tryApproxMaxMax {mkLevelMVar mvarId} := {u₁}"
+      assignLevelMVar mvarId u₁
+      return true
     else return false
 
 private def postponeIsLevelDefEq (lhs : Level) (rhs : Level) : MetaM Unit := do
@@ -97,9 +106,11 @@ mutual
       else if (← isMVarWithGreaterDepth v mvarId) then
         -- If both `u` and `v` are both metavariables, but depth of v is greater, then we assign `v := u`.
         -- This can only happen when levelAssignDepth is set to a smaller value than depth (e.g. during TC synthesis)
+        trace[Meta.isLevelDefEq.step] "{v} := {u}"
         assignLevelMVar v.mvarId! u
         return LBool.true
       else if !u.occurs v then
+        trace[Meta.isLevelDefEq.step] "{u} := {v}"
         assignLevelMVar u.mvarId! v
         return LBool.true
       else if v.isMax && !strictOccursMax u v then
@@ -133,8 +144,9 @@ mutual
   @[export lean_is_level_def_eq]
   partial def isLevelDefEqAuxImpl : Level → Level → MetaM Bool
     | Level.succ lhs, Level.succ rhs => isLevelDefEqAux lhs rhs
-    | lhs, rhs =>
-      withTraceNode `Meta.isLevelDefEq (fun _ => return m!"{lhs} =?= {rhs}") do
+    | lhs, rhs => do
+      withTraceNodeBefore `Meta.isLevelDefEq (fun _ =>
+          withOptions (·.set `pp.instantiateMVars false) do addMessageContext m!"{lhs} =?= {rhs}") do
       if lhs.getLevelOffset == rhs.getLevelOffset then
         return lhs.getOffset == rhs.getOffset
       else

src/Lean/Meta/Sym/Eta.lean

@@ -9,19 +9,37 @@ public import Lean.Meta.Sym.ExprPtr
 public import Lean.Meta.Basic
 import Lean.Meta.Transform
 namespace Lean.Meta.Sym
+
+/--
+Returns `true` if `e` contains a loose bound variable with index in `[0, n)`
+This function assumes `n` is small. If this becomes a bottleneck, we should
+implement a version of `lean_expr_has_loose_bvar` that checks the range in one traversal.
+-/
+def hasLooseBVarsInRange (e : Expr) (n : Nat) : Bool :=
+  e.hasLooseBVars && go n
+where
+  go : Nat → Bool
+  | 0 => false
+  | i+1 => e.hasLooseBVar i || go i
+
 /--
 Checks if `body` is eta-expanded with `n` applications: `f (.bvar (n-1)) ... (.bvar 0)`.
-Returns `f` if so and `f` has no loose bvars; otherwise returns `default`.
+Returns `f` if so and `f` has no loose bvars with indices in the range `[0, n)`; otherwise returns `default`.
 - `n`: number of remaining applications to check
 - `i`: expected bvar index (starts at 0, increments with each application)
 - `default`: returned when not eta-reducible (enables pointer equality check)
 -/
-def etaReduceAux (body : Expr) (n : Nat) (i : Nat) (default : Expr) : Expr := Id.run do
-  match n with
-  | 0 => if body.hasLooseBVars then default else body
-  | n+1 =>
-    let .app f (.bvar j) := body | default
-    if j == i then etaReduceAux f n (i+1) default else default
+def etaReduceAux (body : Expr) (n : Nat) (i : Nat) (default : Expr) : Expr :=
+  go body n i
+where
+  go (body : Expr) (m : Nat) (i : Nat) : Expr := Id.run do
+    match m with
+    | 0 =>
+      if hasLooseBVarsInRange body n then default
+      else body.lowerLooseBVars n n
+    | m+1 =>
+      let .app f (.bvar j) := body | default
+      if j == i then go f m (i+1) else default
 
 /--
 If `e` is of the form `(fun x₁ ... xₙ => f x₁ ... xₙ)` and `f` does not contain `x₁`, ..., `xₙ`,

src/Lean/Meta/Sym/Intro.lean

@@ -48,6 +48,8 @@ def introCore (mvarId : MVarId) (max : Nat) (names : Array Name) : SymM (Array F
     assignDelayedMVar auxMVar.mvarId! fvars mvarId'
     mvarId.assign val
   let finalize (lctx : LocalContext) (localInsts : LocalInstances) (fvars : Array Expr) (type : Expr) : SymM (Array Expr × MVarId) := do
+    if fvars.isEmpty then
+      return (#[], mvarId)
     let type ← instantiateRevS type fvars
     let mvar' ← mkFreshExprMVarAt lctx localInsts type .syntheticOpaque mvarDecl.userName
     let mvarId' := mvar'.mvarId!

src/Lean/Meta/Tactic/Grind/Order/Assert.lean

@@ -148,11 +148,14 @@ def propagatePending : OrderM Unit := do
         - `h₁ : ↑ue' = ue`
         - `h₂ : ↑ve' = ve`
         - `h : ue = ve`
-        **Note**: We currently only support `Nat`. Thus `↑a` is actually
-        `NatCast.natCast a`. If we decide to support arbitrary semirings
-        in this module, we must adjust this code.
+        **Note**: We currently only support `Nat` originals. Thus `↑a` is actually
+        `NatCast.natCast a`. The lemma `nat_eq` is specialized to `Int`, so we
+        only invoke it when the cast destination is `Int`. For other types (e.g.
+        `Rat`), `pushEq ue ve h` above is sufficient and `grind` core can derive
+        the `Nat` equality via `norm_cast`/cast injectivity if needed.
         -/
-        pushEq ue' ve' <| mkApp7 (mkConst ``Grind.Order.nat_eq) ue' ve' ue ve h₁ h₂ h
+        if (← inferType ue) == Int.mkType then
+          pushEq ue' ve' <| mkApp7 (mkConst ``Grind.Order.nat_eq) ue' ve' ue ve h₁ h₂ h
 where
   /--
   If `e` is an auxiliary term used to represent some term `a`, returns
@@ -343,7 +346,7 @@ def getStructIdOf? (e : Expr) : GoalM (Option Nat) := do
   return (← get').exprToStructId.find? { expr := e }
 
 def propagateIneq (e : Expr) : GoalM Unit := do
-  if let some (e', he) := (← get').termMap.find? { expr := e } then
+  if let some { e := e', h := he, .. } := (← get').termMap.find? { expr := e } then
     go e' (some he)
   else
     go e none
@@ -369,20 +372,27 @@ builtin_grind_propagator propagateLT ↓LT.lt := propagateIneq
 public def processNewEq (a b : Expr) : GoalM Unit := do
   unless isSameExpr a b do
     let h ← mkEqProof a b
-    if let some (a', h₁) ← getAuxTerm? a then
-      let some (b', h₂) ← getAuxTerm? b | return ()
+    if let some { e := a', h := h₁, α } ← getAuxTerm? a then
+      let some { e := b', h := h₂, .. } ← getAuxTerm? b | return ()
       /-
       We have
       - `h  : a = b`
       - `h₁ : ↑a = a'`
       - `h₂ : ↑b = b'`
+      where `a'` and `b'` are `NatCast.natCast α inst _` for some type `α`.
       -/
-      let h := mkApp7 (mkConst ``Grind.Order.of_nat_eq) a b a' b' h₁ h₂ h
-      go a' b' h
+      if α == Int.mkType then
+        let h := mkApp7 (mkConst ``Grind.Order.of_nat_eq) a b a' b' h₁ h₂ h
+        go a' b' h
+      else
+        let u ← getDecLevel α
+        let inst ← synthInstance (mkApp (mkConst ``NatCast [u]) α)
+        let h := mkApp9 (mkConst ``Grind.Order.of_natCast_eq [u]) α inst a b a' b' h₁ h₂ h
+        go a' b' h
     else
       go a b h
 where
-  getAuxTerm? (e : Expr) : GoalM (Option (Expr × Expr)) := do
+  getAuxTerm? (e : Expr) : GoalM (Option TermMapEntry) := do
     return (← get').termMap.find? { expr := e }
 
   go (a b h : Expr) : GoalM Unit := do

src/Lean/Meta/Tactic/Grind/Order/Internalize.lean

@@ -166,9 +166,9 @@ def setStructId (e : Expr) : OrderM Unit := do
     exprToStructId := s.exprToStructId.insert { expr := e } structId
   }
 
-def updateTermMap (e eNew h : Expr) : GoalM Unit := do
+def updateTermMap (e eNew h α : Expr) : GoalM Unit := do
   modify' fun s => { s with
-    termMap    := s.termMap.insert { expr := e } (eNew, h)
+    termMap    := s.termMap.insert { expr := e } { e := eNew, h, α }
     termMapInv := s.termMapInv.insert { expr := eNew } (e, h)
   }
 
@@ -198,9 +198,9 @@ where
   getOriginal? (e : Expr) : GoalM (Option Expr) := do
     if let some (e', _) := (← get').termMapInv.find? { expr := e } then
       return some e'
-    let_expr NatCast.natCast _ _ a := e | return none
+    let_expr NatCast.natCast α _ a := e | return none
     if (← alreadyInternalized a) then
-      updateTermMap a e (← mkEqRefl e)
+      updateTermMap a e (← mkEqRefl e) α
       return some a
     else
       return none
@@ -290,7 +290,7 @@ def internalizeTerm (e : Expr) : OrderM Unit := do
 
 open Arith.Cutsat in
 def adaptNat (e : Expr) : GoalM Expr := do
-  if let some (eNew, _) := (← get').termMap.find? { expr := e } then
+  if let some { e := eNew, .. } := (← get').termMap.find? { expr := e } then
     return eNew
   else match_expr e with
     | LE.le _ _ lhs rhs => adaptCnstr lhs rhs (isLT := false)
@@ -307,12 +307,12 @@ where
     let h := mkApp6
         (mkConst (if isLT then ``Nat.ToInt.lt_eq else ``Nat.ToInt.le_eq))
         lhs rhs lhs' rhs' h₁ h₂
-    updateTermMap e eNew h
+    updateTermMap e eNew h (← getIntExpr)
     return eNew
 
   adaptTerm : GoalM Expr := do
     let (eNew, h) ← natToInt e
-    updateTermMap e eNew h
+    updateTermMap e eNew h (← getIntExpr)
     return eNew
 
 def adapt (α : Expr) (e : Expr) : GoalM (Expr × Expr) := do

src/Lean/Meta/Tactic/Grind/Order/Types.lean

@@ -128,6 +128,13 @@ structure Struct where
   propagate          : List ToPropagate := []
   deriving Inhabited
 
+/-- Entry/Value for the map `termMap` in `State` -/
+structure TermMapEntry where
+  e : Expr
+  h : Expr
+  α : Expr
+deriving Inhabited
+
 /-- State for all order types detected by `grind`. -/
 structure State where
   /-- Order structures detected. -/
@@ -143,7 +150,7 @@ structure State where
   Example: given `x y : Nat`, `x ≤ y + 1` is mapped to `Int.ofNat x ≤ Int.ofNat y + 1`, and proof
   of equivalence.
   -/
-  termMap    : PHashMap ExprPtr (Expr × Expr) := {}
+  termMap    : PHashMap ExprPtr TermMapEntry := {}
   /-- `termMap` inverse -/
   termMapInv : PHashMap ExprPtr (Expr × Expr) := {}
   deriving Inhabited

src/Lean/Meta/Tactic/Simp/SimpTheorems.lean

@@ -51,7 +51,7 @@ register_builtin_option debug.tactic.simp.checkDefEqAttr : Bool := {
 }
 
 register_builtin_option warning.simp.varHead : Bool := {
-  defValue := false
+  defValue := true
   descr := "If true, warns when the head symbol of the left-hand side of a `@[simp]` theorem \
     is a variable. Such lemmas are tried on every simp step, which can be slow."
 }

src/Lean/Parser/Do.lean

@@ -66,6 +66,14 @@ def notFollowedByRedefinedTermToken :=
       "do" <|> "dbg_trace" <|> "idbg" <|> "assert!" <|> "debug_assert!" <|> "for" <|> "unless" <|> "return" <|> symbol "try")
     "token at 'do' element"
 
+namespace InternalSyntax
+/--
+Internal syntax used in the `if` and `unless` elaborators. Behaves like `pure PUnit.unit` but
+uses `()` if possible and gives better error messages.
+-/
+scoped syntax (name := doSkip) "skip" : doElem
+end InternalSyntax
+
 @[builtin_doElem_parser] def doLet      := leading_parser
   "let " >> optional "mut " >> letConfig >> letDecl
 @[builtin_doElem_parser] def doLetElse  := leading_parser withPosition <|
@@ -265,6 +273,15 @@ with debug assertions enabled (see the `debugAssertions` option).
 @[builtin_doElem_parser] def doDebugAssert := leading_parser:leadPrec
   "debug_assert! " >> termParser
 
+@[builtin_doElem_parser] def doRepeat      := leading_parser
+  "repeat " >> doSeq
+@[builtin_doElem_parser] def doWhileH      := leading_parser
+  "while " >> ident >> " : " >> withForbidden "do" termParser >> " do " >> doSeq
+@[builtin_doElem_parser] def doWhile       := leading_parser
+  "while " >> withForbidden "do" termParser >> " do " >> doSeq
+@[builtin_doElem_parser] def doRepeatUntil := leading_parser
+  "repeat " >> doSeq >> ppDedent ppLine >> "until " >> termParser
+
 /-
 We use `notFollowedBy` to avoid counterintuitive behavior.
 

src/Lean/PrettyPrinter/Delaborator/Basic.lean

@@ -484,6 +484,7 @@ open SubExpr (Pos PosMap)
 open Delaborator (OptionsPerPos topDownAnalyze DelabM getPPOption)
 
 def delabLevel (l : Level) (prec : Nat) : MetaM Syntax.Level := do
+  let l ← if getPPInstantiateMVars (← getOptions) then instantiateLevelMVars l else pure l
   let mvars := getPPMVarsLevels (← getOptions)
   return Level.quote l prec (mvars := mvars) (lIndex? := (← getMCtx).findLevelIndex?)
 

src/Lean/Server/Completion/SyntheticCompletion.lean

@@ -117,12 +117,13 @@ private partial def isSyntheticTacticCompletion
     (cmdStx   : Syntax)
     : Bool := Id.run do
   let hoverFilePos := fileMap.toPosition hoverPos
-  go hoverFilePos cmdStx 0
+  go hoverFilePos cmdStx 0 none
 where
   go
-      (hoverFilePos : Position)
-      (stx : Syntax)
-      (leadingWs : Nat)
+      (hoverFilePos         : Position)
+      (stx                  : Syntax)
+      (leadingWs            : Nat)
+      (leadingTokenTailPos? : Option String.Pos.Raw)
       : Bool := Id.run do
     match stx.getPos?, stx.getTailPos? with
     | some startPos, some endPos =>
@@ -132,8 +133,9 @@ where
       if ! isCursorInCompletionRange then
         return false
       let mut wsBeforeArg := leadingWs
+      let mut lastArgTailPos? := leadingTokenTailPos?
       for arg in stx.getArgs do
-        if go hoverFilePos arg wsBeforeArg then
+        if go hoverFilePos arg wsBeforeArg lastArgTailPos? then
           return true
         -- We must account for the whitespace before an argument because the syntax nodes we use
         -- to identify tactic blocks only start *after* the whitespace following a `by`, and we
@@ -141,7 +143,12 @@ where
         -- This method of computing whitespace assumes that there are no syntax nodes without tokens
         -- after `by` and before the first proper tactic syntax.
         wsBeforeArg := arg.getTrailingSize
-      return isCompletionInEmptyTacticBlock stx
+        -- Track the tail position of the most recent preceding sibling that has a position so
+        -- that empty tactic blocks (which lack positions) can locate their opening token (e.g.
+        -- the `by` keyword) for indentation checking. The tail position lets us distinguish
+        -- cursors before and after the opener on the opener's line.
+        lastArgTailPos? := arg.getTailPos? <|> lastArgTailPos?
+      return isCompletionInEmptyTacticBlock stx lastArgTailPos?
         || isCompletionAfterSemicolon stx
         || isCompletionOnTacticBlockIndentation hoverFilePos stx
     | _, _ =>
@@ -150,7 +157,7 @@ where
       -- tactic blocks always occur within other syntax with ranges that let us narrow down the
       -- search to the degree that we can be sure that the cursor is indeed in this empty tactic
       -- block.
-      return isCompletionInEmptyTacticBlock stx
+      return isCompletionInEmptyTacticBlock stx leadingTokenTailPos?
 
   isCompletionOnTacticBlockIndentation
       (hoverFilePos : Position)
@@ -190,8 +197,47 @@ where
     else
       none
 
-  isCompletionInEmptyTacticBlock (stx : Syntax) : Bool :=
-    isCursorInProperWhitespace fileMap hoverPos && isEmptyTacticBlock stx
+  isCompletionInEmptyTacticBlock (stx : Syntax) (leadingTokenTailPos? : Option String.Pos.Raw) : Bool := Id.run do
+    if ! isCursorInProperWhitespace fileMap hoverPos then
+      return false
+    if ! isEmptyTacticBlock stx then
+      return false
+    -- Bracketed tactic blocks `{ ... }` are delimited by the braces themselves, so tactics
+    -- inserted in an empty bracketed block can appear at any column between the braces
+    -- (`withoutPosition` disables indentation constraints inside `tacticSeqBracketed`).
+    if stx.getKind == ``Parser.Tactic.tacticSeqBracketed then
+      let some openEndPos := stx[0].getTailPos?
+        | return false
+      let some closeStartPos := stx[2].getPos?
+        | return false
+      return openEndPos.byteIdx <= hoverPos.byteIdx && hoverPos.byteIdx <= closeStartPos.byteIdx
+    return isAtExpectedTacticIndentation leadingTokenTailPos?
+
+  -- After an empty tactic opener like `by`, tactics on a subsequent line must be inserted at an
+  -- increased indentation level (two spaces past the indentation of the line containing the
+  -- opener token). We mirror that here so that tactic completions are not offered in positions
+  -- where a tactic could not actually be inserted. On the same line as the opener, completions
+  -- are allowed only in the trailing whitespace past the opener — cursors earlier on the line
+  -- belong to the surrounding term, not to the tactic block.
+  isAtExpectedTacticIndentation (leadingTokenTailPos? : Option String.Pos.Raw) : Bool := Id.run do
+    let some tokenTailPos := leadingTokenTailPos?
+      | return true
+    let hoverFilePos := fileMap.toPosition hoverPos
+    let tokenTailFilePos := fileMap.toPosition tokenTailPos
+    if hoverFilePos.line == tokenTailFilePos.line then
+      return hoverPos.byteIdx >= tokenTailPos.byteIdx
+    let expectedColumn := countLeadingSpaces (fileMap.lineStart tokenTailFilePos.line) + 2
+    return hoverFilePos.column == expectedColumn
+
+  countLeadingSpaces (pos : String.Pos.Raw) : Nat := Id.run do
+    let mut p := pos
+    let mut n : Nat := 0
+    while ! p.atEnd fileMap.source do
+      if p.get fileMap.source != ' ' then
+        break
+      p := p.next fileMap.source
+      n := n + 1
+    return n
 
   isEmptyTacticBlock (stx : Syntax) : Bool :=
     stx.getKind == ``Parser.Tactic.tacticSeq && isEmpty stx

src/Std/Data/DHashMap/RawDecidableEquiv.lean

@@ -18,7 +18,7 @@ open Std.DHashMap.Internal
 
 namespace Std.DHashMap.Raw
 
-instance instDecidableEquiv {α : Type u} {β : α → Type v} [BEq α] [LawfulBEq α] [Hashable α] [∀ k, BEq (β k)] [∀ k, LawfulBEq (β k)] {m₁ m₂ : Raw α β} (h₁ : m₁.WF) (h₂ : m₂.WF) : Decidable (m₁ ~m m₂) :=
+def instDecidableEquiv {α : Type u} {β : α → Type v} [BEq α] [LawfulBEq α] [Hashable α] [∀ k, BEq (β k)] [∀ k, LawfulBEq (β k)] {m₁ m₂ : Raw α β} (h₁ : m₁.WF) (h₂ : m₂.WF) : Decidable (m₁ ~m m₂) :=
   Raw₀.decidableEquiv ⟨m₁, h₁.size_buckets_pos⟩ ⟨m₂, h₂.size_buckets_pos⟩ h₁ h₂
 
 end Std.DHashMap.Raw

src/Std/Data/DTreeMap/Raw/DecidableEquiv.lean

@@ -19,7 +19,7 @@ open Std.DTreeMap.Internal.Impl
 
 namespace Std.DTreeMap.Raw
 
-instance instDecidableEquiv {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] [∀ k, BEq (β k)] [∀ k, LawfulBEq (β k)] {t₁ t₂ : Raw α β cmp} (h₁ : t₁.WF) (h₂ : t₂.WF) : Decidable (t₁ ~m t₂) :=
+def instDecidableEquiv {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] [∀ k, BEq (β k)] [∀ k, LawfulBEq (β k)] {t₁ t₂ : Raw α β cmp} (h₁ : t₁.WF) (h₂ : t₂.WF) : Decidable (t₁ ~m t₂) :=
   let : Ord α := ⟨cmp⟩;
   let : Decidable (t₁.inner ~m t₂.inner) := decidableEquiv t₁.1 t₂.1 h₁ h₂;
   decidable_of_iff _ ⟨fun h => ⟨h⟩, fun h => h.1⟩

src/Std/Data/HashMap/RawDecidableEquiv.lean

@@ -19,7 +19,7 @@ open Std.DHashMap.Raw
 
 namespace Std.HashMap.Raw
 
-instance instDecidableEquiv {α : Type u} {β : Type v} [BEq α] [LawfulBEq α] [Hashable α] [BEq β] [LawfulBEq β] {m₁ m₂ : Raw α β} (h₁ : m₁.WF) (h₂ : m₂.WF) : Decidable (m₁ ~m m₂) :=
+def instDecidableEquiv {α : Type u} {β : Type v} [BEq α] [LawfulBEq α] [Hashable α] [BEq β] [LawfulBEq β] {m₁ m₂ : Raw α β} (h₁ : m₁.WF) (h₂ : m₂.WF) : Decidable (m₁ ~m m₂) :=
   let : Decidable (m₁.1 ~m m₂.1) := DHashMap.Raw.instDecidableEquiv h₁.out h₂.out;
   decidable_of_iff _ ⟨fun h => ⟨h⟩, fun h => h.1⟩
 

src/Std/Data/HashSet/RawDecidableEquiv.lean

@@ -19,7 +19,7 @@ open Std.HashMap.Raw
 
 namespace Std.HashSet.Raw
 
-instance instDecidableEquiv {α : Type u} [BEq α] [LawfulBEq α] [Hashable α] {m₁ m₂ : Raw α} (h₁ : m₁.WF) (h₂ : m₂.WF) : Decidable (m₁ ~m m₂) :=
+def instDecidableEquiv {α : Type u} [BEq α] [LawfulBEq α] [Hashable α] {m₁ m₂ : Raw α} (h₁ : m₁.WF) (h₂ : m₂.WF) : Decidable (m₁ ~m m₂) :=
   let : Decidable (m₁.1 ~m m₂.1) := HashMap.Raw.instDecidableEquiv h₁.out h₂.out;
   decidable_of_iff _ ⟨fun h => ⟨h⟩, fun h => h.1⟩
 

src/Std/Data/TreeMap/Raw/DecidableEquiv.lean

@@ -20,7 +20,7 @@ open Std.DTreeMap.Raw
 
 namespace Std.TreeMap.Raw
 
-instance instDecidableEquiv {α : Type u} {β : Type v} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] [BEq β] [LawfulBEq β] {t₁ t₂ : Raw α β cmp} (h₁ : t₁.WF) (h₂ : t₂.WF) : Decidable (t₁ ~m t₂) :=
+def instDecidableEquiv {α : Type u} {β : Type v} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] [BEq β] [LawfulBEq β] {t₁ t₂ : Raw α β cmp} (h₁ : t₁.WF) (h₂ : t₂.WF) : Decidable (t₁ ~m t₂) :=
   let : Ord α := ⟨cmp⟩;
   let : Decidable (t₁.inner ~m t₂.inner) := DTreeMap.Raw.instDecidableEquiv h₁ h₂;
   decidable_of_iff _ ⟨fun h => ⟨h⟩, fun h => h.1⟩

src/Std/Data/TreeSet/Raw/DecidableEquiv.lean

@@ -20,7 +20,7 @@ open Std.TreeMap.Raw
 
 namespace Std.TreeSet.Raw
 
-instance instDecidableEquiv {α : Type u} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] {t₁ t₂ : Raw α cmp} (h₁ : t₁.WF) (h₂ : t₂.WF) : Decidable (t₁ ~m t₂) :=
+def instDecidableEquiv {α : Type u} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] {t₁ t₂ : Raw α cmp} (h₁ : t₁.WF) (h₂ : t₂.WF) : Decidable (t₁ ~m t₂) :=
   let : Ord α := ⟨cmp⟩;
   let : Decidable (t₁.inner ~m t₂.inner) := TreeMap.Raw.instDecidableEquiv h₁ h₂;
   decidable_of_iff _ ⟨fun h => ⟨h⟩, fun h => h.1⟩

src/lake/Lake/Build/Common.lean

@@ -235,7 +235,7 @@ public def checkHashUpToDate
 : JobM Bool := (·.isUpToDate) <$> checkHashUpToDate' info depTrace depHash oldTrace
 
 /--
-**Ror internal use only.**
+**For internal use only.**
 Checks whether `info` is up-to-date with the trace.
 If so, replays the log of the trace if available.
 -/
@@ -271,20 +271,24 @@ Returns `true` if the saved trace exists and its hash matches `inputHash`.
 
 If up-to-date, replays the saved log from the trace and sets the current
 build action to `replay`. Otherwise, if the log is empty and trace is synthetic,
-or if the trace is not up-to-date, the build action will be set to `fetch`.
+or if the trace is not up-to-date, the build action will be set to `reuse`.
 -/
-public def SavedTrace.replayOrFetchIfUpToDate (inputHash : Hash) (self : SavedTrace) : JobM Bool := do
+public def SavedTrace.replayCachedIfUpToDate (inputHash : Hash) (self : SavedTrace) : JobM Bool := do
   if let .ok data := self then
     if data.depHash == inputHash then
       if data.synthetic && data.log.isEmpty then
-        updateAction .fetch
+        updateAction .reuse
       else
         updateAction .replay
         data.log.replay
       return true
-  updateAction .fetch
+  updateAction .reuse
   return false
 
+@[deprecated replayCachedIfUpToDate (since := "2026-04-15")]
+public abbrev SavedTrace.replayOrFetchIfUpToDate (inputHash : Hash) (self : SavedTrace) : JobM Bool := do
+  self.replayCachedIfUpToDate inputHash
+
 /-- **For internal use only.** -/
 public class ToOutputJson (α : Type u) where
   toOutputJson (arts : α) : Json
@@ -684,7 +688,7 @@ public def buildArtifactUnlessUpToDate
     let fetchArt? restore := do
       let some (art : XArtifact exe) ← getArtifacts? inputHash savedTrace pkg
         | return none
-      unless (← savedTrace.replayOrFetchIfUpToDate inputHash) do
+      unless (← savedTrace.replayCachedIfUpToDate inputHash) do
         removeFileIfExists file
         writeFetchTrace traceFile inputHash (toJson art.descr)
       if restore then

src/lake/Lake/Build/Job/Basic.lean

@@ -29,11 +29,18 @@ namespace Lake
 public inductive JobAction
 /-- No information about this job's action is available. -/
 | unknown
-/-- Tried to replay a cached build action (set by `buildFileUnlessUpToDate`) -/
+/-- Tried to reuse a cached build (e.g., can be set by `replayCachedIfUpToDate`). -/
+| reuse
+/-- Tried to replay a completed build action (e.g., can be set by `replayIfUpToDate`). -/
 | replay
-/-- Tried to fetch a build from a store (can be set by `buildUnlessUpToDate?`) -/
+/-- Tried to unpack a build from an archive (e.g., unpacking a module `ltar`). -/
+| unpack
+/--
+Tried to fetch a build from a remote store (e.g., set when downloading an artifact
+on-demand from a cache service in `buildArtifactUnlessUpToDate`).
+-/
 | fetch
-/-- Tried to perform a build action (set by `buildUnlessUpToDate?`) -/
+/-- Tried to perform a build action (e.g., set by `buildAction`). -/
 | build
 deriving Inhabited, Repr, DecidableEq, Ord
 
@@ -45,11 +52,13 @@ public instance : Min JobAction := minOfLe
 public instance : Max JobAction := maxOfLe
 
 public def merge (a b : JobAction) : JobAction :=
-  max a b
+  max a b -- inlines `max`
 
-public def verb (failed : Bool) : JobAction → String
+public def verb (failed : Bool) : (self : JobAction) → String
 | .unknown => if failed then "Running" else "Ran"
+| .reuse => if failed then "Reusing" else "Reused"
 | .replay => if failed then "Replaying" else "Replayed"
+| .unpack => if failed then "Unpacking" else "Unpacked"
 | .fetch => if failed then "Fetching" else "Fetched"
 | .build => if failed then "Building" else "Built"
 

src/lake/Lake/Build/Module.lean

@@ -900,8 +900,9 @@ where
     let inputHash := (← getTrace).hash
     let some ltarOrArts ← getArtifacts? inputHash savedTrace mod.pkg
       | return .inr savedTrace
-    match (ltarOrArts : ModuleOutputs)  with
+    match (ltarOrArts : ModuleOutputs) with
     | .ltar ltar =>
+      updateAction .unpack
       mod.clearOutputArtifacts
       mod.unpackLtar ltar.path
       -- Note: This branch implies that only the ltar output is (validly) cached.
@@ -919,7 +920,7 @@ where
       else
         return .inr savedTrace
     | .arts arts =>
-      unless (← savedTrace.replayOrFetchIfUpToDate inputHash) do
+      unless (← savedTrace.replayCachedIfUpToDate inputHash) do
         mod.clearOutputArtifacts
         writeFetchTrace mod.traceFile inputHash (toJson arts.descrs)
       let arts ←

src/lake/Lake/Build/Package.lean

@@ -25,12 +25,8 @@ namespace Lake
 open Lean (Name)
 
 /-- Fetch the package's direct dependencies. -/
-def Package.recFetchDeps (self : Package) : FetchM (Job (Array Package)) := ensureJob do
-  (pure ·) <$> self.depConfigs.mapM fun cfg => do
-    let some dep ← findPackageByName? cfg.name
-      | error s!"{self.prettyName}: package not found for dependency '{cfg.name}' \
-        (this is likely a bug in Lake)"
-    return dep
+def Package.recFetchDeps (self : Package) : FetchM (Job (Array Package)) := do
+  return Job.pure self.depPkgs
 
 /-- The `PackageFacetConfig` for the builtin `depsFacet`. -/
 public def Package.depsFacetConfig : PackageFacetConfig depsFacet :=
@@ -38,10 +34,7 @@ public def Package.depsFacetConfig : PackageFacetConfig depsFacet :=
 
 /-- Compute a topological ordering of the package's transitive dependencies. -/
 def Package.recComputeTransDeps (self : Package) : FetchM (Job (Array Package)) := ensureJob do
-  (pure ·.toArray) <$> self.depConfigs.foldlM (init := OrdPackageSet.empty) fun deps cfg => do
-    let some dep ← findPackageByName? cfg.name
-      | error s!"{self.prettyName}: package not found for dependency '{cfg.name}' \
-        (this is likely a bug in Lake)"
+  (pure ·.toArray) <$> self.depPkgs.foldlM (init := OrdPackageSet.empty) fun deps dep => do
     let depDeps ← (← fetch <| dep.transDeps).await
     return depDeps.foldl (·.insert ·) deps |>.insert dep
 
@@ -153,7 +146,7 @@ def Package.fetchBuildArchive
   let upToDate ← buildUnlessUpToDate? (action := .fetch) archiveFile depTrace traceFile do
     download url archiveFile headers
   unless upToDate && (← self.buildDir.pathExists) do
-    updateAction .fetch
+    updateAction .unpack
     untar archiveFile self.buildDir
 
 @[inline]

src/lake/Lake/Build/Run.lean

@@ -210,7 +210,7 @@ def mkMonitorContext (cfg : BuildConfig) (jobs : JobQueue) : BaseIO MonitorConte
   let failLv := cfg.failLv
   let isVerbose := cfg.verbosity = .verbose
   let showProgress := cfg.showProgress
-  let minAction := if isVerbose then .unknown else .fetch
+  let minAction := if isVerbose then .unknown else .unpack
   let showOptional := isVerbose
   let showTime := isVerbose || !useAnsi
   let updateFrequency := 100

src/lake/Lake/Build/Trace.lean

@@ -9,7 +9,7 @@ prelude
 public import Lean.Data.Json
 import Init.Data.Nat.Fold
 meta import Init.Data.Nat.Fold
-import Lake.Util.String
+public import Lake.Util.String
 public import Init.Data.String.Search
 public import Init.Data.String.Extra
 import Init.Data.Option.Coe
@@ -141,8 +141,8 @@ public def ofHex? (s : String) : Option Hash :=
   if s.utf8ByteSize = 16 && isHex s then ofHex s else none
 
 /-- Returns the hash as 16-digit lowercase hex string. -/
-public def hex (self : Hash) : String :=
-  lpad (String.ofList <| Nat.toDigits 16 self.val.toNat) '0' 16
+@[inline] public def hex (self : Hash) : String :=
+  lowerHexUInt64 self.val
 
 /-- Parse a hash from a string of decimal digits. -/
 public def ofDecimal? (s : String) : Option Hash :=

src/lake/Lake/CLI/Main.lean

@@ -69,7 +69,7 @@ public structure LakeOptions where
   scope? : Option CacheServiceScope := none
   platform? : Option CachePlatform := none
   toolchain? : Option CacheToolchain := none
-  rev? : Option String := none
+  rev? : Option GitRev := none
   maxRevs : Nat := 100
   shake : Shake.Args := {}
 
@@ -563,7 +563,7 @@ private def computePackageRev (pkgDir : FilePath) : CliStateM String := do
   repo.getHeadRevision
 
 private def putCore
-  (rev : String)  (outputs : FilePath) (artDir : FilePath)
+  (rev : GitRev)  (outputs : FilePath) (artDir : FilePath)
   (service : CacheService) (scope : CacheServiceScope)
   (platform := CachePlatform.none) (toolchain := CacheToolchain.none)
 : LoggerIO Unit := do

src/lake/Lake/Config/Cache.lean

@@ -7,6 +7,7 @@ module
 
 prelude
 import Init.Control.Do
+public import Lake.Util.Git
 public import Lake.Util.Log
 public import Lake.Util.Version
 public import Lake.Config.Artifact
@@ -469,7 +470,7 @@ public def readOutputs? (cache : Cache) (scope : String) (inputHash : Hash) : Lo
   cache.dir / "revisions"
 
 /-- Returns path to the input-to-output mappings of a downloaded package revision. -/
-@[inline] public def revisionPath (cache : Cache) (scope : String) (rev : String)   : FilePath :=
+@[inline] public def revisionPath (cache : Cache) (scope : String) (rev : GitRev) : FilePath :=
   cache.revisionDir / scope / s!"{rev}.jsonl"
 
 end Cache
@@ -942,7 +943,7 @@ public def uploadArtifacts
 public def mapContentType : String := "application/vnd.reservoir.outputs+json-lines"
 
 def s3RevisionUrl
-  (rev : String) (service : CacheService) (scope : CacheServiceScope)
+  (rev : GitRev) (service : CacheService) (scope : CacheServiceScope)
   (platform := CachePlatform.none) (toolchain := CacheToolchain.none)
 : String :=
   match scope.impl with
@@ -956,7 +957,7 @@ def s3RevisionUrl
     return s!"{url}/{rev}.jsonl"
 
 public def revisionUrl
-  (rev : String) (service : CacheService) (scope : CacheServiceScope)
+  (rev : GitRev) (service : CacheService) (scope : CacheServiceScope)
   (platform := CachePlatform.none) (toolchain := CacheToolchain.none)
 : String :=
   if service.isReservoir then Id.run do
@@ -974,7 +975,7 @@ public def revisionUrl
     service.s3RevisionUrl rev scope platform toolchain
 
 public def downloadRevisionOutputs?
-  (rev : String) (cache : Cache) (service : CacheService)
+  (rev : GitRev) (cache : Cache) (service : CacheService)
   (localScope : String) (remoteScope : CacheServiceScope)
   (platform := CachePlatform.none) (toolchain := CacheToolchain.none) (force := false)
 : LoggerIO (Option CacheMap) := do
@@ -998,7 +999,7 @@ public def downloadRevisionOutputs?
   CacheMap.load path platform.isNone
 
 public def uploadRevisionOutputs
-  (rev : String) (outputs : FilePath) (service : CacheService) (scope : CacheServiceScope)
+  (rev : GitRev) (outputs : FilePath) (service : CacheService) (scope : CacheServiceScope)
   (platform := CachePlatform.none) (toolchain := CacheToolchain.none)
 : LoggerIO Unit := do
   let url := service.s3RevisionUrl rev scope platform toolchain

src/lake/Lake/Config/Dependency.lean

@@ -9,6 +9,7 @@ prelude
 public import Init.Dynamic
 public import Init.System.FilePath
 public import Lean.Data.NameMap.Basic
+public import Lake.Util.Git
 import Init.Data.ToString.Name
 import Init.Data.ToString.Macro
 
@@ -30,7 +31,7 @@ public inductive DependencySrc where
 /- A package located at a fixed path relative to the dependent package's directory. -/
 | path (dir : FilePath)
 /- A package cloned from a Git repository available at a fixed Git `url`. -/
-| git (url : String) (rev : Option String) (subDir : Option FilePath)
+| git (url : String) (rev : Option GitRev) (subDir : Option FilePath)
 deriving Inhabited, Repr
 
 /--

src/lake/Lake/Config/Package.lean

@@ -52,6 +52,8 @@ public structure Package where
   remoteUrl : String
   /-- Dependency configurations for the package. -/
   depConfigs : Array Dependency := #[]
+  /-- **For internal use only.** Resolved direct dependences of the package. -/
+  depPkgs : Array Package := #[]
   /-- Target configurations in the order declared by the package. -/
   targetDecls : Array (PConfigDecl keyName) := #[]
   /-- Name-declaration map of target configurations in the package. -/

src/lake/Lake/Config/Workspace.lean

@@ -33,14 +33,12 @@ public def computeLakeCache (pkg : Package) (lakeEnv : Lake.Env) : Cache :=
     lakeEnv.lakeCache?.getD ⟨pkg.lakeDir / "cache"⟩
 
 public structure Workspace.Raw : Type where
-  /-- The root package of the workspace. -/
-  root : Package
   /-- The detected {lean}`Lake.Env` of the workspace. -/
   lakeEnv : Lake.Env
   /-- The Lake configuration from the system configuration file. -/
   lakeConfig : LoadedLakeConfig
   /-- The Lake cache. -/
-  lakeCache : Cache := private_decl% computeLakeCache root lakeEnv
+  lakeCache : Cache
   /--
   The CLI arguments Lake was run with.
   Used by {lit}`lake update` to perform a restart of Lake on a toolchain update.
@@ -59,6 +57,7 @@ public structure Workspace.Raw : Type where
   deriving Nonempty
 
 public structure Workspace.Raw.WF (ws : Workspace.Raw) : Prop where
+  size_packages_pos : 0 < ws.packages.size
   packages_wsIdx : ∀ (h : i < ws.packages.size), (ws.packages[i]'h).wsIdx = i
 
 /-- A Lake workspace -- the top-level package directory. -/
@@ -67,8 +66,13 @@ public structure Workspace extends raw : Workspace.Raw, wf : raw.WF
 public instance : Nonempty Workspace := .intro {
   lakeEnv := default
   lakeConfig := Classical.ofNonempty
-  root := Classical.ofNonempty
-  packages_wsIdx h := by simp at h
+  lakeCache := Classical.ofNonempty
+  packages := #[{(Classical.ofNonempty : Package) with wsIdx := 0}]
+  size_packages_pos := by simp
+  packages_wsIdx {i} h := by
+    cases i with
+    | zero => simp
+    | succ => simp at h
 }
 
 public hydrate_opaque_type OpaqueWorkspace Workspace
@@ -85,9 +89,13 @@ public def Package.defaultTargetRoots (self : Package) : Array Lean.Name :=
 
 namespace Workspace
 
+/-- The root package of the workspace. -/
+@[inline] public def root (self : Workspace) : Package :=
+  self.packages[0]'self.size_packages_pos
+
 /-- **For internal use.** Whether this workspace is Lean itself.  -/
-@[inline] def bootstrap (ws : Workspace) : Bool :=
-  ws.root.bootstrap
+@[inline] def bootstrap (self : Workspace) : Bool :=
+  self.root.bootstrap
 
 /-- The path to the workspace's directory (i.e., the directory of the root package). -/
 @[inline] public def dir (self : Workspace) : FilePath :=
@@ -193,12 +201,18 @@ This is configured through {lit}`cache.service` entries in the system Lake confi
   {self with
     packages := self.packages.push pkg
     packageMap := self.packageMap.insert pkg.keyName pkg
+    size_packages_pos := by simp
     packages_wsIdx {i} i_lt := by
       cases Nat.lt_add_one_iff_lt_or_eq.mp <| Array.size_push .. ▸ i_lt with
       | inl i_lt => simpa [Array.getElem_push_lt i_lt] using self.packages_wsIdx i_lt
       | inr i_eq => simpa [i_eq] using h
   }
 
+/-- **For internal use only.** -/
+public theorem packages_addPackage' :
+  (addPackage' pkg ws h).packages = ws.packages.push pkg
+:= by rfl
+
 /-- Add a package to the workspace. -/
 @[inline] public def addPackage (pkg : Package) (self : Workspace) : Workspace :=
   self.addPackage' {pkg with wsIdx := self.packages.size} rfl
@@ -278,6 +292,11 @@ public def findTargetDecl? (name : Name) (self : Workspace) : Option ((pkg : Pac
 @[inline] public def addFacetConfig {name} (cfg : FacetConfig name) (self : Workspace) : Workspace :=
   {self with facetConfigs := self.facetConfigs.insert cfg}
 
+/-- **For internal use only.** -/
+public theorem packages_addFacetConfig :
+  (addFacetConfig cfg ws).packages = ws.packages
+:= by rfl
+
 /-- Try to find a facet configuration in the workspace with the given name. -/
 @[inline] public def findFacetConfig? (name : Name) (self : Workspace) : Option (FacetConfig name) :=
   self.facetConfigs.get? name

src/lake/Lake/Load/Manifest.lean

@@ -8,6 +8,7 @@ module
 prelude
 public import Lake.Util.Version
 public import Lake.Config.Defaults
+public import Lake.Util.Git
 import Lake.Util.Error
 public import Lake.Util.FilePath
 import Lake.Util.JsonObject
@@ -75,8 +76,8 @@ public inductive PackageEntrySrc
   /-- A remote Git package. -/
   | git
     (url : String)
-    (rev : String)
-    (inputRev? : Option String)
+    (rev : GitRev)
+    (inputRev? : Option GitRev)
     (subDir? : Option FilePath)
   deriving Inhabited
 

src/lake/Lake/Load/Materialize.lean

@@ -13,6 +13,8 @@ import Lake.Util.Git
 import Lake.Util.IO
 import Lake.Reservoir
 
+set_option doc.verso true
+
 open System Lean
 
 /-! # Dependency Materialization
@@ -23,9 +25,12 @@ or resolve a local path dependency.
 
 namespace Lake
 
-/-- Update the Git package in `repo` to `rev` if not already at it. -/
+/--
+Update the Git package in {lean}`repo` to the revision {lean}`rev?` if not already at it.
+IF no revision is specified (i.e., {lean}`rev? = none`), then uses the latest {lit}`master`.
+-/
 def updateGitPkg
-  (name : String) (repo : GitRepo) (rev? : Option String)
+  (name : String) (repo : GitRepo) (rev? : Option GitRev)
 : LoggerIO PUnit := do
   let rev ← repo.findRemoteRevision rev?
   if (← repo.getHeadRevision) = rev then
@@ -40,9 +45,9 @@ def updateGitPkg
     -- so stale ones from the previous revision cause incorrect trace computations.
     repo.clean
 
-/-- Clone the Git package as `repo`. -/
+/-- Clone the Git package as {lean}`repo`. -/
 def cloneGitPkg
-  (name : String) (repo : GitRepo) (url : String) (rev? : Option String)
+  (name : String) (repo : GitRepo) (url : String) (rev? : Option GitRev)
 : LoggerIO PUnit := do
   logInfo s!"{name}: cloning {url}"
   repo.clone url
@@ -52,9 +57,9 @@ def cloneGitPkg
     repo.checkoutDetach rev
 
 /--
-Update the Git repository from `url` in `repo` to `rev?`.
-If `repo` is already from `url`, just checkout the new revision.
-Otherwise, delete the local repository and clone a fresh copy from `url`.
+Update the Git repository from {lean}`url` in {lean}`repo` to {lean}`rev?`.
+If {lean}`repo` is already from {lean}`url`, just checkout the new revision.
+Otherwise, delete the local repository and clone a fresh copy from {lean}`url`.
 -/
 def updateGitRepo
   (name : String) (repo : GitRepo) (url : String) (rev? : Option String)
@@ -75,8 +80,9 @@ def updateGitRepo
       IO.FS.removeDirAll repo.dir
       cloneGitPkg name repo url rev?
 
+
 /--
-Materialize the Git repository from `url` into `repo` at `rev?`.
+Materialize the Git repository from {lean}`url` into {lean}`repo` at {lean}`rev?`.
 Clone it if no local copy exists, otherwise update it.
 -/
 def materializeGitRepo
@@ -114,11 +120,11 @@ namespace MaterializedDep
 @[inline] public def scope (self : MaterializedDep) : String :=
   self.manifestEntry.scope
 
-/-- Path to the dependency's manfiest file (relative to `relPkgDir`). -/
+/-- Path to the dependency's manfiest file (relative to {lean}`relPkgDir`). -/
 @[inline] public def relManifestFile? (self : MaterializedDep) : Option FilePath :=
   self.manifestEntry.manifestFile?
 
-/-- Path to the dependency's manfiest file (relative to `relPkgDir`). -/
+/-- Path to the dependency's manfiest file (relative to {lean}`relPkgDir`). -/
 @[inline] public def relManifestFile (self : MaterializedDep) : FilePath :=
   self.relManifestFile?.getD defaultManifestFile
 
@@ -126,7 +132,7 @@ namespace MaterializedDep
 @[inline] public def manifestFile (self : MaterializedDep) : FilePath :=
   self.pkgDir / self.relManifestFile
 
-/-- Path to the dependency's configuration file (relative to `relPkgDir`). -/
+/-- Path to the dependency's configuration file (relative to {lean}`relPkgDir`). -/
 @[inline] public def relConfigFile (self : MaterializedDep) : FilePath :=
   self.manifestEntry.configFile
 
@@ -143,7 +149,7 @@ end MaterializedDep
 
 inductive InputVer
 | none
-| git (rev : String)
+| git (rev : GitRev)
 | ver (ver : VerRange)
 
 def pkgNotIndexed (scope name : String) (ver : InputVer) : String :=

src/lake/Lake/Load/Resolve.lean

@@ -15,6 +15,8 @@ import Lake.Build.Topological
 import Lake.Load.Materialize
 import Lake.Load.Lean.Eval
 import Lake.Load.Package
+import Init.Data.Range.Polymorphic.Iterators
+import Init.TacticsExtra
 
 open System Lean
 
@@ -45,23 +47,29 @@ namespace Lake
 def Workspace.addFacetDecls (decls : Array FacetDecl) (self : Workspace) : Workspace :=
   decls.foldl (·.addFacetConfig ·.config) self
 
+theorem Workspace.packages_addFacetDecls :
+  (addFacetDecls decls ws).packages = ws.packages
+:= by
+  simp only [addFacetDecls]
+  apply Array.foldl_induction (fun _ (s : Workspace) => s.packages = ws.packages) rfl
+  intro i s h
+  simp only [packages_addFacetConfig, h]
+
 /--
 Loads the package configuration of a materialized dependency.
 Adds the package and the facets defined within it to the `Workspace`.
 -/
-def addDepPackage
-  (dep : MaterializedDep)
-  (lakeOpts : NameMap String)
-  (leanOpts : Options) (reconfigure : Bool)
-: StateT Workspace LogIO Package := fun ws => do
+def Workspace.addDepPackage'
+  (ws : Workspace) (dep : MaterializedDep)
+  (lakeOpts : NameMap String) (leanOpts : Options) (reconfigure : Bool)
+: LogIO {ws' : Workspace // ws'.packages.size = ws.packages.size + 1} := do
   let wsIdx := ws.packages.size
   let loadCfg := mkDepLoadConfig ws dep lakeOpts leanOpts reconfigure
   let ⟨loadCfg, h⟩ ← resolveConfigFile dep.prettyName loadCfg
   let fileCfg ← loadConfigFile loadCfg h
   let pkg := mkPackage loadCfg fileCfg wsIdx
-  let ws := ws.addPackage' pkg wsIdx_mkPackage
-  let ws := ws.addFacetDecls fileCfg.facetDecls
-  return (pkg, ws)
+  let ws := ws.addPackage' pkg wsIdx_mkPackage |>.addFacetDecls fileCfg.facetDecls
+  return ⟨ws, by simp [ws, packages_addFacetDecls, packages_addPackage']⟩
 
 /--
 The resolver's call stack of dependencies.
@@ -103,6 +111,52 @@ abbrev ResolveT m := DepStackT <| StateT Workspace m
     recFetchAcyclic (·.baseName) go root
   return ws
 
+def Workspace.setDepPkgs
+  (self : Workspace) (wsIdx : Nat) (depPkgs : Array Package)
+: Workspace := {self with
+  packages := self.packages.modify wsIdx ({· with depPkgs})
+  size_packages_pos := by simp [self.size_packages_pos]
+  packages_wsIdx {i} := by
+    if h : wsIdx = i then
+      simp [h, Array.getElem_modify_self, self.packages_wsIdx]
+    else
+      simp [Array.getElem_modify_of_ne h, self.packages_wsIdx]
+}
+
+structure ResolveState where
+  ws : Workspace
+  depIdxs : Array Nat
+  lt_of_mem : ∀ i ∈ depIdxs, i < ws.packages.size
+
+namespace ResolveState
+
+@[inline] def init (ws : Workspace) (size : Nat) : ResolveState :=
+  {ws, depIdxs := Array.mkEmpty size, lt_of_mem := by simp}
+
+@[inline] def reuseDep (s : ResolveState) (wsIdx : Fin s.ws.packages.size) : ResolveState :=
+  have lt_of_mem := by
+    intro i i_mem
+    cases Array.mem_push.mp i_mem with
+    | inl i_mem => exact s.lt_of_mem i i_mem
+    | inr i_eq => simp only [i_eq, wsIdx.isLt]
+  {s with depIdxs := s.depIdxs.push wsIdx, lt_of_mem}
+
+@[inline] def newDep
+  (s : ResolveState) (dep : MaterializedDep)
+  (lakeOpts : NameMap String) (leanOpts : Options) (reconfigure : Bool)
+: LogIO ResolveState := do
+  let ⟨ws, depIdxs, lt_of_mem⟩ := s
+  let wsIdx := ws.packages.size
+  let ⟨ws', h⟩ ← ws.addDepPackage' dep lakeOpts leanOpts reconfigure
+  have lt_of_mem := by
+    intro i i_mem
+    cases Array.mem_push.mp i_mem with
+    | inl i_mem => exact h ▸ Nat.lt_add_one_of_lt (lt_of_mem i i_mem)
+    | inr i_eq => simp only [wsIdx, i_eq, h, Nat.lt_add_one]
+  return ⟨ws', depIdxs.push wsIdx, lt_of_mem⟩
+
+end ResolveState
+
 /-
 Recursively visits each node in a package's dependency graph, starting from
 the workspace package `root`. Each dependency missing from the workspace is
@@ -121,19 +175,31 @@ See `Workspace.updateAndMaterializeCore` for more details.
 : m Workspace := do
   ws.runResolveT go root stack
 where
-  @[specialize] go pkg recurse : ResolveT m Unit := do
-    let start := (← getWorkspace).packages.size
+  @[specialize] go pkg recurse : ResolveT m Unit := fun depStack ws => do
+    let start := ws.packages.size
     -- Materialize and load the missing direct dependencies of `pkg`
-    pkg.depConfigs.forRevM fun dep => do
-      let ws ← getWorkspace
-      if ws.packages.any (·.baseName == dep.name) then
-        return -- already handled in another branch
+    let s := ResolveState.init ws pkg.depConfigs.size
+    let ⟨ws, depIdxs, lt_of_mem⟩ ← pkg.depConfigs.foldrM (m := m) (init := s) fun dep s => do
+      if let some wsIdx := s.ws.packages.findFinIdx? (·.baseName == dep.name) then
+        return s.reuseDep wsIdx -- already handled in another branch
       if pkg.baseName = dep.name then
         error s!"{pkg.prettyName}: package requires itself (or a package with the same name)"
-      let matDep ← resolve pkg dep (← getWorkspace)
-      discard <| addDepPackage matDep dep.opts leanOpts reconfigure
+      let matDep ← resolve pkg dep s.ws
+      s.newDep matDep dep.opts leanOpts reconfigure
+    let depsEnd := ws.packages.size
     -- Recursively load the dependencies' dependencies
-    (← getWorkspace).packages.forM recurse start
+    let ws ← ws.packages.foldlM (start := start) (init := ws) fun ws pkg =>
+      (·.2) <$> recurse pkg depStack ws
+    -- Add the package's dependencies to the package
+    let ws :=
+      if h_le : depsEnd ≤ ws.packages.size then
+        ws.setDepPkgs pkg.wsIdx <| depIdxs.attach.map fun ⟨wsIdx, h_mem⟩ =>
+          ws.packages[wsIdx]'(Nat.lt_of_lt_of_le (lt_of_mem wsIdx h_mem) h_le)
+      else
+        have : Inhabited Workspace := ⟨ws⟩
+        panic! "workspace shrunk" -- should be unreachable
+    return ((), ws)
+
 
 /--
 Adds monad state used to update the manifest.
@@ -372,10 +438,14 @@ def Workspace.updateAndMaterializeCore
     let start := ws.packages.size
     let ws ← (deps.zip matDeps).foldlM (init := ws) fun ws (dep, matDep) => do
       addDependencyEntries matDep
-      let (_, ws) ← addDepPackage matDep dep.opts leanOpts true ws
+      let ⟨ws, _⟩ ← ws.addDepPackage' matDep dep.opts leanOpts true
       return ws
-    ws.packages.foldlM (init := ws) (start := start) fun ws pkg =>
+    let stop := ws.packages.size
+    let ws ← ws.packages.foldlM (init := ws) (start := start) fun ws pkg =>
       ws.resolveDepsCore updateAndAddDep pkg [ws.root.baseName] leanOpts true
+    -- Set dependency packages after `resolveDepsCore` so
+    -- that the dependencies' dependencies are also properly set
+    return ws.setDepPkgs ws.root.wsIdx ws.packages[start...<stop]
   else
     ws.resolveDepsCore updateAndAddDep (leanOpts := leanOpts) (reconfigure := true)
 where

src/lake/Lake/Load/Workspace.lean

@@ -35,17 +35,22 @@ public def loadWorkspaceRoot (config : LoadConfig) : LogIO Workspace := do
   let ⟨config, h⟩ ← resolveConfigFile "[root]" config
   let fileCfg ← loadConfigFile config h
   let root := mkPackage config fileCfg 0
+  have wsIdx_root : root.wsIdx = 0 := wsIdx_mkPackage
   let facetConfigs := fileCfg.facetDecls.foldl (·.insert ·.config) initFacetConfigs
-  let ws : Workspace := {
-    root
+  return {
     lakeEnv := config.lakeEnv
+    lakeCache := computeLakeCache root config.lakeEnv
     lakeConfig
     lakeArgs? := config.lakeArgs?
     facetConfigs
-    packages_wsIdx h := by simp at h
+    packages := #[root]
+    packageMap := DNameMap.empty.insert root.keyName root
+    size_packages_pos := by simp
+    packages_wsIdx {i} h := by
+      cases i with
+      | zero => simp [wsIdx_root]
+      | succ => simp at h
   }
-  let ws := ws.addPackage' root wsIdx_mkPackage
-  return ws
 
 /--
 Load a `Workspace` for a Lake package by

src/lake/Lake/Util/Family.lean

@@ -154,6 +154,7 @@ public class FamilyOut {α : Type u} {β : Type v} (f : α → β) (a : α) (b :
 -- Simplifies proofs involving open type families.
 -- Scoped to avoid slowing down `simp` in downstream projects (the discrimination
 -- tree key is `_`, so it would be attempted on every goal).
+set_option warning.simp.varHead false in
 attribute [scoped simp] FamilyOut.fam_eq
 
 public instance [FamilyDef f a b] : FamilyOut f a b where

src/lake/Lake/Util/Git.lean

@@ -10,6 +10,7 @@ public import Init.Data.ToString
 public import Lake.Util.Proc
 import Init.Data.String.TakeDrop
 import Init.Data.String.Search
+import Lake.Util.String
 
 open System
 namespace Lake
@@ -36,18 +37,48 @@ public def filterUrl? (url : String) : Option String :=
     some url
 
 public def isFullObjectName (rev : String) : Bool :=
-  rev.length == 40 && rev.all fun c => c.isDigit || ('a' <= c && c <= 'f')
+  rev.utf8ByteSize == 40 && isHex rev
 
 end Git
 
 public structure GitRepo where
   dir : FilePath
 
-public instance : Coe FilePath GitRepo := ⟨(⟨·⟩)⟩
-public instance : ToString GitRepo := ⟨(·.dir.toString)⟩
+
+/--
+A commit-ish [Git revision][1].
+
+This can be SHA1 commit hash, a branch name, or one of Git's more complex specifiers.
+
+[1]: https://git-scm.com/docs/gitrevisions#_specifying_revisions
+-/
+public abbrev GitRev := String
+
+namespace GitRev
+
+/-- The head revision (i.e., `HEAD`). -/
+@[expose] public def head : GitRev := "HEAD"
+
+/-- The revision fetched during the last `git fetch` (i.e., `FETCH_HEAD`). -/
+@[expose] public def fetchHead : GitRev := "FETCH_HEAD"
+
+/-- Returns whether this revision is a 40-digit hexadecimal (SHA1) commit hash. -/
+public def isFullSha1 (rev : GitRev) : Bool :=
+  rev.utf8ByteSize == 40 && isHex rev
+
+attribute [deprecated GitRev.isFullSha1 (since := "2026-04-17")] Git.isFullObjectName
+
+/-- Scopes the revision by the remote. -/
+@[inline] public def withRemote (remote : String) (rev : GitRev) : GitRev :=
+  s!"{remote}/{rev}"
+
+end GitRev
 
 namespace GitRepo
 
+public instance : Coe FilePath GitRepo := ⟨(⟨·⟩)⟩
+public instance : ToString GitRepo := ⟨(·.dir.toString)⟩
+
 public def cwd : GitRepo := ⟨"."⟩
 
 @[inline] public def dirExists (repo : GitRepo) : BaseIO Bool :=
@@ -71,12 +102,18 @@ public def clone (url : String) (repo : GitRepo) : LogIO PUnit  :=
 public def quietInit (repo : GitRepo) : LogIO PUnit  :=
   repo.execGit #["init", "-q"]
 
+public def bareInit (repo : GitRepo) : LogIO PUnit  :=
+  repo.execGit #["init", "--bare", "-q"]
+
 public def insideWorkTree (repo : GitRepo) : BaseIO Bool := do
   repo.testGit #["rev-parse", "--is-inside-work-tree"]
 
 public def fetch (repo : GitRepo) (remote := Git.defaultRemote) : LogIO PUnit  :=
   repo.execGit #["fetch", "--tags", "--force", remote]
 
+public def addWorktreeDetach (path : FilePath) (rev : GitRev) (repo : GitRepo) : LogIO PUnit :=
+  repo.execGit #["worktree", "add", "--detach", path.toString, rev]
+
 public def checkoutBranch (branch : String) (repo : GitRepo) : LogIO PUnit :=
   repo.execGit #["checkout", "-B", branch]
 
@@ -87,60 +124,80 @@ public def checkoutDetach (hash : String) (repo : GitRepo) : LogIO PUnit  :=
 public def clean (repo : GitRepo) : LogIO PUnit :=
   repo.execGit #["clean", "-xf"]
 
-public def resolveRevision? (rev : String) (repo : GitRepo) : BaseIO (Option String) := do
+/-- Resolves the revision to a Git object name (SHA1 hash) which or may not exist in the repository. -/
+public def resolveRevision? (rev : GitRev) (repo : GitRepo) : BaseIO (Option GitRev) := do
   repo.captureGit? #["rev-parse", "--verify", "--end-of-options", rev]
 
-public def resolveRevision (rev : String) (repo : GitRepo) : LogIO String := do
-  if Git.isFullObjectName rev then return rev
+/-- Resolves the revision to a valid commit hash within the repository. -/
+public def findCommit? (rev : GitRev) (repo : GitRepo) : BaseIO  (Option GitRev) := do
+  repo.captureGit? #["rev-parse", "--verify", "--end-of-options", rev ++ "^{commit}"]
+
+public def resolveRevision (rev : GitRev) (repo : GitRepo) : LogIO GitRev := do
+  if rev.isFullSha1 then return rev
   if let some rev ← repo.resolveRevision? rev then return rev
   error s!"{repo}: revision not found '{rev}'"
 
-@[inline] public def getHeadRevision? (repo : GitRepo) : BaseIO (Option String) :=
-  repo.resolveRevision? "HEAD"
+@[inline] public def getHeadRevision? (repo : GitRepo) : BaseIO (Option GitRev) :=
+  repo.resolveRevision? .head
 
-public def getHeadRevision (repo : GitRepo) : LogIO String := do
+public def getHeadRevision (repo : GitRepo) : LogIO GitRev := do
   if let some rev ← repo.getHeadRevision? then return rev
   error s!"{repo}: could not resolve 'HEAD' to a commit; \
     the repository may be corrupt, so you may need to remove it and try again"
 
-public def getHeadRevisions (repo : GitRepo) (n : Nat := 0) : LogIO (Array String) := do
+public def fetchRevision? (repo : GitRepo) (remote : String) (rev : GitRev) : LogIO (Option GitRev) := do
+  if (← repo.testGit #["fetch", "--tags", "--force", "--refetch", "--filter=tree:0", remote, rev]) then
+    let some rev ← repo.resolveRevision? .fetchHead
+      | error s!"{repo}: could not resolve 'FETCH_HEAD' to a commit after fetching; \
+          this may be an issue with Lake; please report it"
+    return rev
+  else
+    return none
+
+public def getHeadRevisions (repo : GitRepo) (n : Nat := 0) : LogIO (Array GitRev) := do
   let args := #["rev-list", "HEAD"]
   let args := if n != 0 then args ++ #["-n", toString n] else args
   let revs ← repo.captureGit args
   return revs.split '\n' |>.toStringArray
 
-public def resolveRemoteRevision (rev : String) (remote := Git.defaultRemote) (repo : GitRepo) : LogIO String := do
-  if Git.isFullObjectName rev then return rev
-  if let some rev ← repo.resolveRevision? s!"{remote}/{rev}"  then return rev
+public def resolveRemoteRevision (rev : GitRev) (remote := Git.defaultRemote) (repo : GitRepo) : LogIO GitRev := do
+  if rev.isFullSha1 then return rev
+  if let some rev ← repo.resolveRevision? (rev.withRemote remote) then return rev
   if let some rev ← repo.resolveRevision? rev then return rev
   error s!"{repo}: revision not found '{rev}'"
 
-public def findRemoteRevision (repo : GitRepo) (rev? : Option String := none) (remote := Git.defaultRemote) : LogIO String := do
+public def findRemoteRevision (repo : GitRepo) (rev? : Option GitRev := none) (remote := Git.defaultRemote) : LogIO String := do
   repo.fetch remote; repo.resolveRemoteRevision (rev?.getD Git.upstreamBranch) remote
 
-public def branchExists (rev : String) (repo : GitRepo) : BaseIO Bool := do
+public def branchExists (rev : GitRev) (repo : GitRepo) : BaseIO Bool := do
   repo.testGit #["show-ref", "--verify", s!"refs/heads/{rev}"]
 
-public def revisionExists (rev : String) (repo : GitRepo) : BaseIO Bool := do
+public def revisionExists (rev : GitRev) (repo : GitRepo) : BaseIO Bool := do
   repo.testGit #["rev-parse", "--verify", rev ++ "^{commit}"]
 
 public def getTags (repo : GitRepo) : BaseIO (List String) := do
   let some out ← repo.captureGit? #["tag"] | return []
   return out.split '\n' |>.toStringList
 
-public def findTag? (rev : String := "HEAD") (repo : GitRepo) : BaseIO (Option String) := do
+public def findTag? (rev : GitRev := .head) (repo : GitRepo) : BaseIO (Option String) := do
   repo.captureGit? #["describe", "--tags", "--exact-match", rev]
 
 public def getRemoteUrl?
   (remote := Git.defaultRemote) (repo : GitRepo)
-: BaseIO (Option String) := do repo.captureGit? #["remote", "get-url", remote]
+: BaseIO (Option String) := repo.captureGit? #["remote", "get-url", remote]
+
+public def addRemote (remote : String) (url : String) (repo : GitRepo) : LogIO Unit :=
+  repo.execGit #["remote", "add", remote, url]
+
+public def setRemoteUrl (remote : String) (url : String) (repo : GitRepo) : LogIO Unit :=
+  repo.execGit #["remote", "set-url", remote, url]
 
 public def getFilteredRemoteUrl?
   (remote := Git.defaultRemote) (repo : GitRepo)
 : BaseIO (Option String) := OptionT.run do Git.filterUrl? (← repo.getRemoteUrl? remote)
 
 public def hasNoDiff (repo : GitRepo) : BaseIO Bool := do
-  repo.testGit #["diff", "HEAD", "--exit-code"]
+  repo.testGit #["diff", "--exit-code", "HEAD"]
 
 @[inline] public def hasDiff (repo : GitRepo) : BaseIO Bool := do
   not <$> repo.hasNoDiff

src/lake/Lake/Util/String.lean

@@ -7,6 +7,7 @@ module
 
 prelude
 public import Init.Data.ToString.Basic
+import Init.Data.UInt.Lemmas
 import Init.Data.String.Basic
 import Init.Data.Nat.Fold
 
@@ -33,3 +34,38 @@ public def isHex (s : String) : Bool :=
       65 ≤ c -- 'A'
     else
       false
+
+def lowerHexByte (n : UInt8) : UInt8 :=
+  if n ≤ 9 then
+    n + 48 -- + '0'
+  else
+    n + 87 -- + ('a' - 10)
+
+theorem isValidChar_of_lt_256 (h : n < 256) : isValidChar n :=
+  Or.inl <| Nat.lt_trans h (by decide)
+
+def lowerHexChar (n : UInt8) : Char :=
+  ⟨lowerHexByte n |>.toUInt32, isValidChar_of_lt_256 <|
+     UInt32.lt_iff_toNat_lt.mpr <| (lowerHexByte n).toNat_lt⟩
+
+public def lowerHexUInt64 (n : UInt64) : String :=
+  String.ofByteArray (ByteArray.emptyWithCapacity 16) ByteArray.isValidUTF8_empty
+  |>.push (lowerHexChar (n >>> 60 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 56 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 52 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 48 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 44 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 40 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 36 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 32 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 28 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 24 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 20 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 16 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 12 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 8 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n >>> 4 &&& 0xf).toUInt8)
+  |>.push (lowerHexChar (n &&& 0xf).toUInt8)
+
+-- sanity check
+example : "0123456789abcdef" = lowerHexUInt64 0x0123456789abcdef := by decide

src/runtime/CMakeLists.txt

@@ -39,7 +39,7 @@ if(USE_MIMALLOC)
   # Lean code includes it as `lean/mimalloc.h` but for compiling `static.c` itself, add original dir
   include_directories(${LEAN_BINARY_DIR}/../mimalloc/src/mimalloc/include)
   # make all symbols visible, always build with optimizations as otherwise Lean becomes too slow
-  set(MIMALLOC_FLAGS "-DMI_SHARED_LIB -DMI_SHARED_LIB_EXPORT -O3 -DNDEBUG -DMI_WIN_NOREDIRECT -Wno-unused-function")
+  set(MIMALLOC_FLAGS "-DMI_SHARED_LIB -DMI_SHARED_LIB_EXPORT -O3 -DNDEBUG -DMI_WIN_NOREDIRECT -DMI_SECURE=${LEAN_MI_SECURE} -Wno-unused-function")
   if(CMAKE_CXX_COMPILER_ID MATCHES "AppleClang|Clang")
     string(APPEND MIMALLOC_FLAGS " -Wno-deprecated")
   endif()

src/runtime/io.cpp

@@ -752,6 +752,7 @@ extern "C" LEAN_EXPORT obj_res lean_windows_get_next_transition(b_obj_arg timezo
     u_strToUTF8(dst_name, sizeof(dst_name), &dst_name_len, tzID, tzIDLength, &status);
 
     if (U_FAILURE(status)) {
+        ucal_close(cal);
         return lean_io_result_mk_error(lean_mk_io_error_invalid_argument(EINVAL, mk_string("failed to convert DST name to UTF-8")));
     }
 
@@ -1397,7 +1398,7 @@ extern "C" LEAN_EXPORT obj_res lean_io_app_path() {
     memset(dest, 0, PATH_MAX);
     pid_t pid = getpid();
     snprintf(path, PATH_MAX, "/proc/%d/exe", pid);
-    if (readlink(path, dest, PATH_MAX) == -1) {
+    if (readlink(path, dest, PATH_MAX - 1) == -1) {
         return io_result_mk_error("failed to locate application");
     } else {
         return io_result_mk_ok(mk_string(dest));

src/stdlib.make.in

@@ -54,7 +54,7 @@ ifeq "${USE_LAKE}" "ON"
 
 # build in parallel
 Init:
-	${PREV_STAGE}/bin/lake build -f ${CMAKE_BINARY_DIR}/lakefile.toml $(LAKE_EXTRA_ARGS)
+	${PREV_STAGE}/bin/lake build -f ${CMAKE_BINARY_DIR}/lakefile.toml ${LEAN_EXTRA_LAKE_OPTS} $(LAKE_EXTRA_ARGS)
 
 Std Lean Lake Leanc LeanChecker LeanIR: Init