fix: circular assignment at structure instance elaborator

This PR fixes a stack overflow caused by a cyclic assignment in the
metavariable context. The cycle is unintentionally introduced by the
structure instance elaborator.

closes #3150

.github/workflows/pr-body.yml

@@ -1,6 +1,7 @@
 name: Check PR body for changelog convention
 
 on:
+  merge_group:
   pull_request:
     types: [opened, synchronize, reopened, edited, labeled, converted_to_draft, ready_for_review]
 
@@ -9,6 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check PR body
+        if: github.event_name == 'pull_request'
         uses: actions/github-script@v7
         with:
           script: |

src/Init/Core.lean

@@ -1922,12 +1922,12 @@ represents an element of `Squash α` the same as `α` itself
 `Squash.lift` will extract a value in any subsingleton `β` from a function on `α`,
 while `Nonempty.rec` can only do the same when `β` is a proposition.
 -/
-def Squash (α : Type u) := Quot (fun (_ _ : α) => True)
+def Squash (α : Sort u) := Quot (fun (_ _ : α) => True)
 
 /-- The canonical quotient map into `Squash α`. -/
-def Squash.mk {α : Type u} (x : α) : Squash α := Quot.mk _ x
+def Squash.mk {α : Sort u} (x : α) : Squash α := Quot.mk _ x
 
-theorem Squash.ind {α : Type u} {motive : Squash α → Prop} (h : ∀ (a : α), motive (Squash.mk a)) : ∀ (q : Squash α), motive q :=
+theorem Squash.ind {α : Sort u} {motive : Squash α → Prop} (h : ∀ (a : α), motive (Squash.mk a)) : ∀ (q : Squash α), motive q :=
   Quot.ind h
 
 /-- If `β` is a subsingleton, then a function `α → β` lifts to `Squash α → β`. -/

src/Init/Data/Array/Subarray.lean

@@ -15,15 +15,6 @@ structure Subarray (α : Type u)  where
   start_le_stop : start ≤ stop
   stop_le_array_size : stop ≤ array.size
 
-@[deprecated Subarray.array (since := "2024-04-13")]
-abbrev Subarray.as (s : Subarray α) : Array α := s.array
-
-@[deprecated Subarray.start_le_stop (since := "2024-04-13")]
-theorem Subarray.h₁ (s : Subarray α) : s.start ≤ s.stop := s.start_le_stop
-
-@[deprecated Subarray.stop_le_array_size (since := "2024-04-13")]
-theorem Subarray.h₂ (s : Subarray α) : s.stop ≤ s.array.size := s.stop_le_array_size
-
 namespace Subarray
 
 def size (s : Subarray α) : Nat :=

src/Init/Data/BitVec/Basic.lean

@@ -29,9 +29,6 @@ section Nat
 
 instance natCastInst : NatCast (BitVec w) := ⟨BitVec.ofNat w⟩
 
-@[deprecated isLt (since := "2024-03-12")]
-theorem toNat_lt (x : BitVec n) : x.toNat < 2^n := x.isLt
-
 /-- Theorem for normalizing the bit vector literal representation. -/
 -- TODO: This needs more usage data to assess which direction the simp should go.
 @[simp, bv_toNat] theorem ofNat_eq_ofNat : @OfNat.ofNat (BitVec n) i _ = .ofNat n i := rfl

src/Init/Data/Fin/Lemmas.lean

@@ -642,7 +642,7 @@ theorem pred_add_one (i : Fin (n + 2)) (h : (i : Nat) < n + 1) :
   ext
   simp
 
-@[simp] theorem subNat_one_succ (i : Fin (n + 1)) (h : 1 ≤ ↑i) : (subNat 1 i h).succ = i := by
+@[simp] theorem subNat_one_succ (i : Fin (n + 1)) (h : 1 ≤ (i : Nat)) : (subNat 1 i h).succ = i := by
   ext
   simp
   omega

src/Init/Data/Nat/Linear.lean

@@ -52,25 +52,23 @@ def Poly.denote (ctx : Context) (p : Poly) : Nat :=
   | [] => 0
   | (k, v) :: p => Nat.add (Nat.mul k (v.denote ctx)) (denote ctx p)
 
-def Poly.insertSorted (k : Nat) (v : Var) (p : Poly) : Poly :=
+def Poly.insert (k : Nat) (v : Var) (p : Poly) : Poly :=
   match p with
   | [] => [(k, v)]
-  | (k', v') :: p => bif Nat.blt v v' then (k, v) :: (k', v') :: p else (k', v') :: insertSorted k v p
+  | (k', v') :: p =>
+    bif Nat.blt v v' then
+      (k, v) :: (k', v') :: p
+    else bif Nat.beq v v' then
+      (k + k', v') :: p
+    else
+      (k', v') :: insert k v p
 
-def Poly.sort (p : Poly) : Poly :=
-  let rec go (p : Poly) (r : Poly) : Poly :=
+def Poly.norm (p : Poly) : Poly := go p []
+where
+  go (p : Poly) (r : Poly) : Poly :=
     match p with
     | [] => r
-    | (k, v) :: p => go p (r.insertSorted k v)
-  go p []
-
-def Poly.fuse (p : Poly) : Poly :=
-  match p with
-  | []  => []
-  | (k, v) :: p =>
-    match fuse p with
-    | [] => [(k, v)]
-    | (k', v') :: p' => bif v == v' then (Nat.add k k', v)::p' else (k, v) :: (k', v') :: p'
+    | (k, v) :: p => go p (r.insert k v)
 
 def Poly.mul (k : Nat) (p : Poly) : Poly :=
   bif k == 0 then
@@ -146,15 +144,17 @@ def Poly.combineAux (fuel : Nat) (p₁ p₂ : Poly) : Poly :=
 def Poly.combine (p₁ p₂ : Poly) : Poly :=
   combineAux hugeFuel p₁ p₂
 
-def Expr.toPoly : Expr → Poly
-  | Expr.num k    => bif k == 0 then [] else [ (k, fixedVar) ]
-  | Expr.var i    => [(1, i)]
-  | Expr.add a b  => a.toPoly ++ b.toPoly
-  | Expr.mulL k a => a.toPoly.mul k
-  | Expr.mulR a k => a.toPoly.mul k
-
-def Poly.norm (p : Poly) : Poly :=
-  p.sort.fuse
+def Expr.toPoly (e : Expr) :=
+  go 1 e []
+where
+  -- Implementation note: This assembles the result using difference lists
+  -- to avoid `++` on lists.
+  go (coeff : Nat) : Expr → (Poly → Poly)
+    | Expr.num k    => bif k == 0 then id else ((coeff * k, fixedVar) :: ·)
+    | Expr.var i    => ((coeff, i) :: ·)
+    | Expr.add a b  => go coeff a ∘ go coeff b
+    | Expr.mulL k a
+    | Expr.mulR a k => bif k == 0 then id else go (coeff * k) a
 
 def Expr.toNormPoly (e : Expr) : Poly :=
   e.toPoly.norm
@@ -201,7 +201,7 @@ def PolyCnstr.denote (ctx : Context) (c : PolyCnstr) : Prop :=
     Poly.denote_le ctx (c.lhs, c.rhs)
 
 def PolyCnstr.norm (c : PolyCnstr) : PolyCnstr :=
-  let (lhs, rhs) := Poly.cancel c.lhs.sort.fuse c.rhs.sort.fuse
+  let (lhs, rhs) := Poly.cancel c.lhs.norm c.rhs.norm
   { eq := c.eq, lhs, rhs }
 
 def PolyCnstr.isUnsat (c : PolyCnstr) : Bool :=
@@ -268,24 +268,32 @@ def PolyCnstr.toExpr (c : PolyCnstr) : ExprCnstr :=
   { c with lhs := c.lhs.toExpr, rhs := c.rhs.toExpr }
 
 attribute [local simp] Nat.add_comm Nat.add_assoc Nat.add_left_comm Nat.right_distrib Nat.left_distrib Nat.mul_assoc Nat.mul_comm
-attribute [local simp] Poly.denote Expr.denote Poly.insertSorted Poly.sort Poly.sort.go Poly.fuse Poly.cancelAux
+attribute [local simp] Poly.denote Expr.denote Poly.insert Poly.norm Poly.norm.go Poly.cancelAux
 attribute [local simp] Poly.mul Poly.mul.go
 
-theorem Poly.denote_insertSorted (ctx : Context) (k : Nat) (v : Var) (p : Poly) : (p.insertSorted k v).denote ctx = p.denote ctx + k * v.denote ctx := by
+theorem Poly.denote_insert (ctx : Context) (k : Nat) (v : Var) (p : Poly) :
+    (p.insert k v).denote ctx = p.denote ctx + k * v.denote ctx := by
   match p with
   | [] => simp
-  | (k', v') :: p => by_cases h : Nat.blt v v' <;> simp [h, denote_insertSorted]
+  | (k', v') :: p =>
+    by_cases h₁ : Nat.blt v v'
+    · simp [h₁]
+    · by_cases h₂ : Nat.beq v v'
+      · simp only [insert, h₁, h₂, cond_false, cond_true]
+        simp [Nat.eq_of_beq_eq_true h₂]
+      · simp only [insert, h₁, h₂, cond_false, cond_true]
+        simp [denote_insert]
 
-attribute [local simp] Poly.denote_insertSorted
+attribute [local simp] Poly.denote_insert
 
-theorem Poly.denote_sort_go (ctx : Context) (p : Poly) (r : Poly) : (sort.go p r).denote ctx = p.denote ctx + r.denote ctx := by
+theorem Poly.denote_norm_go (ctx : Context) (p : Poly) (r : Poly) : (norm.go p r).denote ctx = p.denote ctx + r.denote ctx := by
   match p with
   | [] => simp
-  | (k, v):: p => simp [denote_sort_go]
+  | (k, v):: p => simp [denote_norm_go]
 
-attribute [local simp] Poly.denote_sort_go
+attribute [local simp] Poly.denote_norm_go
 
-theorem Poly.denote_sort (ctx : Context) (m : Poly) : m.sort.denote ctx = m.denote ctx := by
+theorem Poly.denote_sort (ctx : Context) (m : Poly) : m.norm.denote ctx = m.denote ctx := by
   simp
 
 attribute [local simp] Poly.denote_sort
@@ -316,18 +324,6 @@ theorem Poly.denote_reverse (ctx : Context) (p : Poly) : denote ctx (List.revers
 
 attribute [local simp] Poly.denote_reverse
 
-theorem Poly.denote_fuse (ctx : Context) (p : Poly) : p.fuse.denote ctx = p.denote ctx := by
-  match p with
-  | [] => rfl
-  | (k, v) :: p =>
-    have ih := denote_fuse ctx p
-    simp
-    split
-    case _ h => simp [← ih, h]
-    case _ k' v' p' h => by_cases he : v == v' <;> simp [he, ← ih, h]; rw [eq_of_beq he]
-
-attribute [local simp] Poly.denote_fuse
-
 theorem Poly.denote_mul (ctx : Context) (k : Nat) (p : Poly) : (p.mul k).denote ctx = k * p.denote ctx := by
   simp
   by_cases h : k == 0 <;> simp [h]; simp [eq_of_beq h]
@@ -516,13 +512,25 @@ theorem Poly.denote_combine (ctx : Context) (p₁ p₂ : Poly) : (p₁.combine p
 
 attribute [local simp] Poly.denote_combine
 
+theorem Expr.denote_toPoly_go (ctx : Context) (e : Expr) :
+  (toPoly.go k e p).denote ctx = k * e.denote ctx + p.denote ctx := by
+  induction k, e using Expr.toPoly.go.induct generalizing p with
+  | case1 k k' =>
+    simp only [toPoly.go]
+    by_cases h : k' == 0
+    · simp [h, eq_of_beq h]
+    · simp [h, Var.denote]
+  | case2 k i => simp [toPoly.go]
+  | case3 k a b iha ihb => simp [toPoly.go, iha, ihb]
+  | case4 k k' a ih
+  | case5 k a k' ih =>
+    simp only [toPoly.go, denote, mul_eq]
+    by_cases h : k' == 0
+    · simp [h, eq_of_beq h]
+    · simp [h, cond_false, ih, Nat.mul_assoc]
+
 theorem Expr.denote_toPoly (ctx : Context) (e : Expr) : e.toPoly.denote ctx = e.denote ctx := by
-  induction e with
-  | num k => by_cases h : k == 0 <;> simp [toPoly, h, Var.denote]; simp [eq_of_beq h]
-  | var i => simp [toPoly]
-  | add a b iha ihb => simp [toPoly, iha, ihb]
-  | mulL k a ih => simp [toPoly, ih, -Poly.mul]
-  | mulR k a ih => simp [toPoly, ih, -Poly.mul]
+  simp [toPoly, Expr.denote_toPoly_go]
 
 attribute [local simp] Expr.denote_toPoly
 
@@ -554,8 +562,8 @@ theorem ExprCnstr.denote_toPoly (ctx : Context) (c : ExprCnstr) : c.toPoly.denot
   cases c; rename_i eq lhs rhs
   simp [ExprCnstr.denote, PolyCnstr.denote, ExprCnstr.toPoly];
   by_cases h : eq = true <;> simp [h]
-  · simp [Poly.denote_eq, Expr.toPoly]
-  · simp [Poly.denote_le, Expr.toPoly]
+  · simp [Poly.denote_eq]
+  · simp [Poly.denote_le]
 
 attribute [local simp] ExprCnstr.denote_toPoly
 

src/Init/Data/Option/Basic.lean

@@ -16,10 +16,6 @@ def getM [Alternative m] : Option α → m α
   | none     => failure
   | some a   => pure a
 
-@[deprecated getM (since := "2024-04-17")]
--- `[Monad m]` is not needed here.
-def toMonad [Monad m] [Alternative m] : Option α → m α := getM
-
 /-- Returns `true` on `some x` and `false` on `none`. -/
 @[inline] def isSome : Option α → Bool
   | some _ => true
@@ -28,8 +24,6 @@ def toMonad [Monad m] [Alternative m] : Option α → m α := getM
 @[simp] theorem isSome_none : @isSome α none = false := rfl
 @[simp] theorem isSome_some : isSome (some a) = true := rfl
 
-@[deprecated isSome (since := "2024-04-17"), inline] def toBool : Option α → Bool := isSome
-
 /-- Returns `true` on `none` and `false` on `some x`. -/
 @[inline] def isNone : Option α → Bool
   | some _ => false

src/Init/Data/SInt/Basic.lean

@@ -148,6 +148,9 @@ instance : ShiftLeft Int8   := ⟨Int8.shiftLeft⟩
 instance : ShiftRight Int8  := ⟨Int8.shiftRight⟩
 instance : DecidableEq Int8 := Int8.decEq
 
+@[extern "lean_bool_to_int8"]
+def Bool.toInt8 (b : Bool) : Int8 := if b then 1 else 0
+
 @[extern "lean_int8_dec_lt"]
 def Int8.decLt (a b : Int8) : Decidable (a < b) :=
   inferInstanceAs (Decidable (a.toBitVec.slt b.toBitVec))
@@ -249,6 +252,9 @@ instance : ShiftLeft Int16   := ⟨Int16.shiftLeft⟩
 instance : ShiftRight Int16  := ⟨Int16.shiftRight⟩
 instance : DecidableEq Int16 := Int16.decEq
 
+@[extern "lean_bool_to_int16"]
+def Bool.toInt16 (b : Bool) : Int16 := if b then 1 else 0
+
 @[extern "lean_int16_dec_lt"]
 def Int16.decLt (a b : Int16) : Decidable (a < b) :=
   inferInstanceAs (Decidable (a.toBitVec.slt b.toBitVec))
@@ -354,6 +360,9 @@ instance : ShiftLeft Int32   := ⟨Int32.shiftLeft⟩
 instance : ShiftRight Int32  := ⟨Int32.shiftRight⟩
 instance : DecidableEq Int32 := Int32.decEq
 
+@[extern "lean_bool_to_int32"]
+def Bool.toInt32 (b : Bool) : Int32 := if b then 1 else 0
+
 @[extern "lean_int32_dec_lt"]
 def Int32.decLt (a b : Int32) : Decidable (a < b) :=
   inferInstanceAs (Decidable (a.toBitVec.slt b.toBitVec))
@@ -463,6 +472,9 @@ instance : ShiftLeft Int64   := ⟨Int64.shiftLeft⟩
 instance : ShiftRight Int64  := ⟨Int64.shiftRight⟩
 instance : DecidableEq Int64 := Int64.decEq
 
+@[extern "lean_bool_to_int64"]
+def Bool.toInt64 (b : Bool) : Int64 := if b then 1 else 0
+
 @[extern "lean_int64_dec_lt"]
 def Int64.decLt (a b : Int64) : Decidable (a < b) :=
   inferInstanceAs (Decidable (a.toBitVec.slt b.toBitVec))
@@ -574,6 +586,9 @@ instance : ShiftLeft ISize   := ⟨ISize.shiftLeft⟩
 instance : ShiftRight ISize  := ⟨ISize.shiftRight⟩
 instance : DecidableEq ISize := ISize.decEq
 
+@[extern "lean_bool_to_isize"]
+def Bool.toISize (b : Bool) : ISize := if b then 1 else 0
+
 @[extern "lean_isize_dec_lt"]
 def ISize.decLt (a b : ISize) : Decidable (a < b) :=
   inferInstanceAs (Decidable (a.toBitVec.slt b.toBitVec))

src/Init/Data/String/Basic.lean

@@ -514,9 +514,6 @@ instance : Inhabited String := ⟨""⟩
 
 instance : Append String := ⟨String.append⟩
 
-@[deprecated push (since := "2024-04-06")]
-def str : String → Char → String := push
-
 @[inline] def pushn (s : String) (c : Char) (n : Nat) : String :=
   n.repeat (fun s => s.push c) s
 

src/Init/Data/UInt/Basic.lean

@@ -56,6 +56,9 @@ instance : Xor UInt8       := ⟨UInt8.xor⟩
 instance : ShiftLeft UInt8  := ⟨UInt8.shiftLeft⟩
 instance : ShiftRight UInt8 := ⟨UInt8.shiftRight⟩
 
+@[extern "lean_bool_to_uint8"]
+def Bool.toUInt8 (b : Bool) : UInt8 := if b then 1 else 0
+
 @[extern "lean_uint8_dec_lt"]
 def UInt8.decLt (a b : UInt8) : Decidable (a < b) :=
   inferInstanceAs (Decidable (a.toBitVec < b.toBitVec))
@@ -116,6 +119,9 @@ instance : Xor UInt16       := ⟨UInt16.xor⟩
 instance : ShiftLeft UInt16  := ⟨UInt16.shiftLeft⟩
 instance : ShiftRight UInt16 := ⟨UInt16.shiftRight⟩
 
+@[extern "lean_bool_to_uint16"]
+def Bool.toUInt16 (b : Bool) : UInt16 := if b then 1 else 0
+
 set_option bootstrap.genMatcherCode false in
 @[extern "lean_uint16_dec_lt"]
 def UInt16.decLt (a b : UInt16) : Decidable (a < b) :=
@@ -174,6 +180,9 @@ instance : Xor UInt32       := ⟨UInt32.xor⟩
 instance : ShiftLeft UInt32  := ⟨UInt32.shiftLeft⟩
 instance : ShiftRight UInt32 := ⟨UInt32.shiftRight⟩
 
+@[extern "lean_bool_to_uint32"]
+def Bool.toUInt32 (b : Bool) : UInt32 := if b then 1 else 0
+
 @[extern "lean_uint64_add"]
 def UInt64.add (a b : UInt64) : UInt64 := ⟨a.toBitVec + b.toBitVec⟩
 @[extern "lean_uint64_sub"]
@@ -278,5 +287,8 @@ instance : Xor USize        := ⟨USize.xor⟩
 instance : ShiftLeft USize  := ⟨USize.shiftLeft⟩
 instance : ShiftRight USize := ⟨USize.shiftRight⟩
 
+@[extern "lean_bool_to_usize"]
+def Bool.toUSize (b : Bool) : USize := if b then 1 else 0
+
 instance : Max USize := maxOfLe
 instance : Min USize := minOfLe

src/Init/Tactics.lean

@@ -466,7 +466,7 @@ hypotheses or the goal. It can have one of the forms:
 * `at h₁ h₂ ⊢`: target the hypotheses `h₁` and `h₂`, and the goal
 * `at *`: target all hypotheses and the goal
 -/
-syntax location := withPosition(" at" (locationWildcard <|> locationHyp))
+syntax location := withPosition(ppGroup(" at" (locationWildcard <|> locationHyp)))
 
 /--
 * `change tgt'` will change the goal from `tgt` to `tgt'`,

src/Lean/Data/NameMap.lean

@@ -33,6 +33,16 @@ def find? (m : NameMap α) (n : Name) : Option α := RBMap.find? m n
 instance : ForIn m (NameMap α) (Name × α) :=
   inferInstanceAs (ForIn _ (RBMap ..) ..)
 
+/-- `filter f m` returns the `NameMap` consisting of all
+"`key`/`val`"-pairs in `m` where `f key val` returns `true`. -/
+def filter (f : Name → α → Bool) (m : NameMap α) : NameMap α := RBMap.filter f m
+
+/-- `filterMap f m` filters an `NameMap` and simultaneously modifies the filtered values.
+
+It takes a function `f : Name → α → Option β` and applies `f name` to the value with key `name`.
+The resulting entries with non-`none` value are collected to form the output `NameMap`. -/
+def filterMap (f : Name → α → Option β) (m : NameMap α) : NameMap β := RBMap.filterMap f m
+
 end NameMap
 
 def NameSet := RBTree Name Name.quickCmp
@@ -53,6 +63,9 @@ def append (s t : NameSet) : NameSet :=
 instance : Append NameSet where
   append := NameSet.append
 
+/-- `filter f s` returns the `NameSet` consisting of all `x` in `s` where `f x` returns `true`. -/
+def filter (f : Name → Bool) (s : NameSet) : NameSet := RBTree.filter f s
+
 end NameSet
 
 def NameSSet := SSet Name
@@ -73,6 +86,9 @@ instance : EmptyCollection NameHashSet := ⟨empty⟩
 instance : Inhabited NameHashSet := ⟨{}⟩
 def insert (s : NameHashSet) (n : Name) := Std.HashSet.insert s n
 def contains (s : NameHashSet) (n : Name) : Bool := Std.HashSet.contains s n
+
+/-- `filter f s` returns the `NameHashSet` consisting of all `x` in `s` where `f x` returns `true`. -/
+def filter (f : Name → Bool) (s : NameHashSet) : NameHashSet := Std.HashSet.filter f s
 end NameHashSet
 
 def MacroScopesView.isPrefixOf (v₁ v₂ : MacroScopesView) : Bool :=

src/Lean/Data/RBMap.lean

@@ -404,6 +404,24 @@ def intersectBy {γ : Type v₁} {δ : Type v₂} (mergeFn : α → β → γ
       | some b₂ => acc.insert a <| mergeFn a b₁ b₂
       | none => acc
 
+/--
+`filter f m` returns the `RBMap` consisting of all
+"`key`/`val`"-pairs in `m` where `f key val` returns `true`.
+-/
+def filter (f : α → β → Bool) (m : RBMap α β cmp) : RBMap α β cmp :=
+  m.fold (fun r k v => if f k v then r.insert k v else r) {}
+
+/--
+`filterMap f m` filters an `RBMap` and simultaneously modifies the filtered values.
+
+It takes a function `f : α → β → Option γ` and applies `f k v` to the value with key `k`.
+The resulting entries with non-`none` value are collected to form the output `RBMap`.
+-/
+def filterMap (f : α → β → Option γ) (m : RBMap α β cmp) : RBMap α γ cmp :=
+  m.fold (fun r k v => match f k v with
+    | none => r
+    | some b => r.insert k b) {}
+
 end RBMap
 
 def rbmapOf {α : Type u} {β : Type v} (l : List (α × β)) (cmp : α → α → Ordering) : RBMap α β cmp :=

src/Lean/Data/RBTree.lean

@@ -114,6 +114,13 @@ def union (t₁ t₂ : RBTree α cmp) : RBTree α cmp :=
 def diff (t₁ t₂ : RBTree α cmp) : RBTree α cmp :=
   t₂.fold .erase t₁
 
+/--
+`filter f m` returns the `RBTree` consisting of all
+`x` in `m` where `f x` returns `true`.
+-/
+def filter (f : α → Bool) (m : RBTree α cmp) : RBTree α cmp :=
+  RBMap.filter (fun a _ => f a) m
+
 end RBTree
 
 def rbtreeOf {α : Type u} (l : List α) (cmp : α → α → Ordering) : RBTree α cmp :=

src/Lean/Elab/Command.lean

@@ -214,7 +214,7 @@ private def addTraceAsMessagesCore (ctx : Context) (log : MessageLog) (traceStat
   let mut log := log
   let traces' := traces.toArray.qsort fun ((a, _), _) ((b, _), _) => a < b
   for ((pos, endPos), traceMsg) in traces' do
-    let data := .tagged `_traceMsg <| .joinSep traceMsg.toList "\n"
+    let data := .tagged `trace <| .joinSep traceMsg.toList "\n"
     log := log.add <| mkMessageCore ctx.fileName ctx.fileMap data .information pos endPos
   return log
 

src/Lean/Elab/PreDefinition/Nonrec/Eqns.lean

@@ -50,7 +50,9 @@ private partial def mkProof (declName : Name) (type : Expr) : MetaM Expr := do
         go mvarId
       else if let some mvarId ← whnfReducibleLHS? mvarId then
         go mvarId
-      else match (← simpTargetStar mvarId { config.dsimp := false } (simprocs := {})).1 with
+      else
+        let ctx ← Simp.mkContext (config := { dsimp := false })
+        match (← simpTargetStar mvarId ctx (simprocs := {})).1 with
         | TacticResultCNM.closed => return ()
         | TacticResultCNM.modified mvarId => go mvarId
         | TacticResultCNM.noChange =>

src/Lean/Elab/PreDefinition/Structural/Eqns.lean

@@ -45,7 +45,9 @@ where
       go mvarId
     else if let some mvarId ← simpIf? mvarId then
       go mvarId
-    else match (← simpTargetStar mvarId {} (simprocs := {})).1 with
+    else
+      let ctx ← Simp.mkContext
+      match (← simpTargetStar mvarId ctx (simprocs := {})).1 with
       | TacticResultCNM.closed => return ()
       | TacticResultCNM.modified mvarId => go mvarId
       | TacticResultCNM.noChange =>

src/Lean/Elab/PreDefinition/WF/Eqns.lean

@@ -57,7 +57,9 @@ private partial def mkProof (declName : Name) (type : Expr) : MetaM Expr := do
         go mvarId
       else if let some mvarId ← whnfReducibleLHS? mvarId then
         go mvarId
-      else match (← simpTargetStar mvarId { config.dsimp := false } (simprocs := {})).1 with
+      else
+        let ctx ← Simp.mkContext (config := { dsimp := false })
+        match (← simpTargetStar mvarId ctx (simprocs := {})).1 with
         | TacticResultCNM.closed => return ()
         | TacticResultCNM.modified mvarId => go mvarId
         | TacticResultCNM.noChange =>

src/Lean/Elab/PreDefinition/WF/Fix.lean

@@ -227,7 +227,7 @@ def mkFix (preDef : PreDefinition) (prefixArgs : Array Expr) (argsPacker : ArgsP
     -- decreasing goals when the function has only one non fixed argument.
     -- This renaming is irrelevant if the function has multiple non fixed arguments. See `process*` functions above.
     let lctx := (← getLCtx).setUserName x.fvarId! varName
-    withTheReader Meta.Context (fun ctx => { ctx with lctx }) do
+    withLCtx' lctx do
       let F   := xs[1]!
       let val := preDef.value.beta (prefixArgs.push x)
       let val ← processSumCasesOn x F val fun x F val => do

src/Lean/Elab/PreDefinition/WF/GuessLex.lean

@@ -166,7 +166,7 @@ def mayOmitSizeOf (is_mutual : Bool) (args : Array Expr) (x : Expr) : MetaM Bool
 def withUserNames {α} (xs : Array Expr) (ns : Array Name) (k : MetaM α) : MetaM α := do
   let mut lctx ←  getLCtx
   for x in xs, n in ns do lctx := lctx.setUserName x.fvarId! n
-  withTheReader Meta.Context (fun ctx => { ctx with lctx }) k
+  withLCtx' lctx k
 
 /-- Create one measure for each (eligible) parameter of the given predefintion.  -/
 def simpleMeasures (preDefs : Array PreDefinition) (fixedPrefixSize : Nat)

src/Lean/Elab/StructInst.lean

@@ -900,8 +900,16 @@ partial def tryToSynthesizeDefault (structs : Array Struct) (allStructNames : Ar
           | none   =>
             let mvarDecl ← getMVarDecl mvarId
             let val ← ensureHasType mvarDecl.type val
-            mvarId.assign val
-            return true
+            /-
+            We must use `checkedAssign` here to ensure we do not create a cyclic
+            assignment. See #3150.
+            This can happen when there are holes in the the fields the default value
+            depends on.
+            Possible improvement: create a new `_` instead of returning `false` when
+            `checkedAssign` fails. Reason: the field will not be needed after the
+            other `_` are resolved by the user.
+            -/
+            mvarId.checkedAssign val
       | _ => loop (i+1) dist
     else
       return false

src/Lean/Elab/Tactic/BVDecide/Frontend/Normalize.lean

@@ -198,11 +198,10 @@ def rewriteRulesPass (maxSteps : Nat) : Pass where
     let sevalThms ← getSEvalTheorems
     let sevalSimprocs ← Simp.getSEvalSimprocs
 
-    let simpCtx : Simp.Context := {
-      config := { failIfUnchanged := false, zetaDelta := true, maxSteps }
-      simpTheorems := #[bvThms, sevalThms]
-      congrTheorems := (← getSimpCongrTheorems)
-    }
+    let simpCtx ← Simp.mkContext
+      (config := { failIfUnchanged := false, zetaDelta := true, maxSteps })
+      (simpTheorems := #[bvThms, sevalThms])
+      (congrTheorems := (← getSimpCongrTheorems))
 
     let hyps ← goal.getNondepPropHyps
     let ⟨result?, _⟩ ← simpGoal goal
@@ -283,11 +282,10 @@ def embeddedConstraintPass (maxSteps : Nat) : Pass where
 
       let goal ← goal.tryClearMany duplicates
 
-      let simpCtx : Simp.Context := {
-        config := { failIfUnchanged := false, maxSteps }
-        simpTheorems := relevantHyps
-        congrTheorems := (← getSimpCongrTheorems)
-      }
+      let simpCtx ← Simp.mkContext
+        (config := { failIfUnchanged := false, maxSteps })
+        (simpTheorems := relevantHyps)
+        (congrTheorems := (← getSimpCongrTheorems))
 
       let ⟨result?, _⟩ ← simpGoal goal (ctx := simpCtx) (fvarIdsToSimp := ← goal.getNondepPropHyps)
       let some (_, newGoal) := result? | return none

src/Lean/Elab/Tactic/Conv/Pattern.lean

@@ -12,11 +12,10 @@ namespace Lean.Elab.Tactic.Conv
 open Meta
 
 private def getContext : MetaM Simp.Context := do
-  return {
-    simpTheorems  := {}
-    congrTheorems := (← getSimpCongrTheorems)
-    config        := Simp.neutralConfig
-  }
+  Simp.mkContext
+    (simpTheorems  := {})
+    (congrTheorems := (← getSimpCongrTheorems))
+    (config        := Simp.neutralConfig)
 
 partial def matchPattern? (pattern : AbstractMVarsResult) (e : Expr) : MetaM (Option (Expr × Array Expr)) :=
   withNewMCtxDepth do
@@ -126,7 +125,7 @@ private def pre (pattern : AbstractMVarsResult) (state : IO.Ref PatternMatchStat
         pure (.occs #[] 0 ids.toList)
       | _ => throwUnsupportedSyntax
     let state ← IO.mkRef occs
-    let ctx := { ← getContext with config.memoize := occs matches .all _ }
+    let ctx := (← getContext).setMemoize (occs matches .all _)
     let (result, _) ← Simp.main lhs ctx (methods := { pre := pre patternA state })
     let subgoals ← match ← state.get with
     | .all #[] | .occs _ 0 _ =>

src/Lean/Elab/Tactic/NormCast.lean

@@ -28,8 +28,10 @@ def proveEqUsing (s : SimpTheorems) (a b : Expr) : MetaM (Option Simp.Result) :=
     unless ← isDefEq a'.expr b'.expr do return none
     a'.mkEqTrans (← b'.mkEqSymm b)
   withReducible do
-    (go (← Simp.mkDefaultMethods).toMethodsRef
-      { simpTheorems := #[s], congrTheorems := ← Meta.getSimpCongrTheorems }).run' {}
+    let ctx ← Simp.mkContext
+        (simpTheorems := #[s])
+        (congrTheorems := ← Meta.getSimpCongrTheorems)
+    (go (← Simp.mkDefaultMethods).toMethodsRef ctx).run' {}
 
 /-- Proves `a = b` by simplifying using move and squash lemmas. -/
 def proveEqUsingDown (a b : Expr) : MetaM (Option Simp.Result) := do
@@ -191,19 +193,25 @@ def derive (e : Expr) : MetaM Simp.Result := do
   -- step 1: pre-processing of numerals
   let r ← withTrace "pre-processing numerals" do
     let post e := return Simp.Step.done (← try numeralToCoe e catch _ => pure {expr := e})
-    r.mkEqTrans (← Simp.main r.expr { config, congrTheorems } (methods := { post })).1
+    let ctx ← Simp.mkContext (config := config) (congrTheorems := congrTheorems)
+    r.mkEqTrans (← Simp.main r.expr ctx (methods := { post })).1
 
   -- step 2: casts are moved upwards and eliminated
   let r ← withTrace "moving upward, splitting and eliminating" do
     let post := upwardAndElim (← normCastExt.up.getTheorems)
-    r.mkEqTrans (← Simp.main r.expr { config, congrTheorems } (methods := { post })).1
+    let ctx ← Simp.mkContext (config := config) (congrTheorems := congrTheorems)
+    r.mkEqTrans (← Simp.main r.expr ctx (methods := { post })).1
 
   let simprocs ← ({} : Simp.SimprocsArray).add `reduceCtorEq false
 
   -- step 3: casts are squashed
   let r ← withTrace "squashing" do
     let simpTheorems := #[← normCastExt.squash.getTheorems]
-    r.mkEqTrans (← simp r.expr { simpTheorems, config, congrTheorems } simprocs).1
+    let ctx ← Simp.mkContext
+      (config := config)
+      (simpTheorems := simpTheorems)
+      (congrTheorems := congrTheorems)
+    r.mkEqTrans (← simp r.expr ctx simprocs).1
 
   return r
 
@@ -263,7 +271,7 @@ def evalConvNormCast : Tactic :=
 def evalPushCast : Tactic := fun stx => do
   let { ctx, simprocs, dischargeWrapper } ← withMainContext do
     mkSimpContext (simpTheorems := pushCastExt.getTheorems) stx (eraseLocal := false)
-  let ctx := { ctx with config := { ctx.config with failIfUnchanged := false } }
+  let ctx := ctx.setFailIfUnchanged false
   dischargeWrapper.with fun discharge? =>
     discard <| simpLocation ctx simprocs discharge? (expandOptLocation stx[5])
 

src/Lean/Elab/Tactic/Omega/Frontend.lean

@@ -6,7 +6,6 @@ Authors: Kim Morrison
 prelude
 import Lean.Elab.Tactic.Omega.Core
 import Lean.Elab.Tactic.FalseOrByContra
-import Lean.Meta.Tactic.Cases
 import Lean.Elab.Tactic.Config
 
 /-!
@@ -520,23 +519,6 @@ partial def processFacts (p : MetaProblem) : OmegaM (MetaProblem × Nat) := do
 
 end MetaProblem
 
-/--
-Given `p : P ∨ Q` (or any inductive type with two one-argument constructors),
-split the goal into two subgoals:
-one containing the hypothesis `h : P` and another containing `h : Q`.
--/
-def cases₂ (mvarId : MVarId) (p : Expr) (hName : Name := `h) :
-    MetaM ((MVarId × FVarId) × (MVarId × FVarId)) := do
-  let mvarId ← mvarId.assert `hByCases (← inferType p) p
-  let (fvarId, mvarId) ← mvarId.intro1
-  let #[s₁, s₂] ← mvarId.cases fvarId #[{ varNames := [hName] }, { varNames := [hName] }] |
-    throwError "'cases' tactic failed, unexpected number of subgoals"
-  let #[Expr.fvar f₁ ..] ← pure s₁.fields
-    | throwError "'cases' tactic failed, unexpected new hypothesis"
-  let #[Expr.fvar f₂ ..] ← pure s₂.fields
-    | throwError "'cases' tactic failed, unexpected new hypothesis"
-  return ((s₁.mvarId, f₁), (s₂.mvarId, f₂))
-
 /--
 Helpful error message when omega cannot find a solution
 -/
@@ -628,33 +610,36 @@ mutual
 Split a disjunction in a `MetaProblem`, and if we find a new usable fact
 call `omegaImpl` in both branches.
 -/
-partial def splitDisjunction (m : MetaProblem) (g : MVarId) : OmegaM Unit := g.withContext do
+partial def splitDisjunction (m : MetaProblem) : OmegaM Expr := do
   match m.disjunctions with
     | [] => throwError "omega could not prove the goal:\n{← formatErrorMessage m.problem}"
-    | h :: t =>
-      trace[omega] "Case splitting on {← inferType h}"
-      let ctx ← getMCtx
-      let (⟨g₁, h₁⟩, ⟨g₂, h₂⟩) ← cases₂ g h
-      trace[omega] "Adding facts:\n{← g₁.withContext <| inferType (.fvar h₁)}"
-      let m₁ := { m with facts := [.fvar h₁], disjunctions := t }
-      let r ← withoutModifyingState do
-        let (m₁, n) ← g₁.withContext m₁.processFacts
+    | h :: t => do
+      let hType ← whnfD (← inferType h)
+      trace[omega] "Case splitting on {hType}"
+      let_expr Or hType₁ hType₂ := hType | throwError "Unexpected disjunction {hType}"
+      let p?₁ ← withoutModifyingState do withLocalDeclD `h₁ hType₁ fun h₁ => do
+        withTraceNode `omega (msg := fun _ => do pure m!"Assuming fact:{indentExpr hType₁}") do
+        let m₁ := { m with facts := [h₁], disjunctions := t }
+        let (m₁, n) ← m₁.processFacts
         if 0 < n then
-          omegaImpl m₁ g₁
-          pure true
+          let p₁ ← omegaImpl m₁
+          let p₁ ← mkLambdaFVars #[h₁] p₁
+          return some p₁
         else
-          pure false
-      if r then
-        trace[omega] "Adding facts:\n{← g₂.withContext <| inferType (.fvar h₂)}"
-        let m₂ := { m with facts := [.fvar h₂], disjunctions := t }
-        omegaImpl m₂ g₂
+          return none
+      if let some p₁ := p?₁ then
+         withLocalDeclD `h₂ hType₂ fun h₂ => do
+          withTraceNode `omega (msg := fun _ => do pure m!"Assuming fact:{indentExpr hType₂}") do
+          let m₂ := { m with facts := [h₂], disjunctions := t }
+          let p₂ ← omegaImpl m₂
+          let p₂ ← mkLambdaFVars #[h₂] p₂
+          return mkApp6 (mkConst ``Or.elim) hType₁ hType₂ (mkConst ``False) h p₁ p₂
       else
         trace[omega] "No new facts found."
-        setMCtx ctx
-        splitDisjunction { m with disjunctions := t } g
+        splitDisjunction { m with disjunctions := t }
 
 /-- Implementation of the `omega` algorithm, and handling disjunctions. -/
-partial def omegaImpl (m : MetaProblem) (g : MVarId) : OmegaM Unit := g.withContext do
+partial def omegaImpl (m : MetaProblem) : OmegaM Expr := do
   let (m, _) ← m.processFacts
   guard m.facts.isEmpty
   let p := m.problem
@@ -663,12 +648,12 @@ partial def omegaImpl (m : MetaProblem) (g : MVarId) : OmegaM Unit := g.withCont
   trace[omega] "After elimination:\nAtoms: {← atomsList}\n{p'}"
   match p'.possible, p'.proveFalse?, p'.proveFalse?_spec with
   | true, _, _ =>
-    splitDisjunction m g
+    splitDisjunction m
   | false, .some prf, _ =>
     trace[omega] "Justification:\n{p'.explanation?.get}"
     let prf ← instantiateMVars (← prf)
     trace[omega] "omega found a contradiction, proving {← inferType prf}"
-    g.assign prf
+    return prf
 
 end
 
@@ -677,7 +662,9 @@ Given a collection of facts, try prove `False` using the omega algorithm,
 and close the goal using that.
 -/
 def omega (facts : List Expr) (g : MVarId) (cfg : OmegaConfig := {}) : MetaM Unit :=
-  OmegaM.run (omegaImpl { facts } g) cfg
+  g.withContext do
+    let prf ← OmegaM.run (omegaImpl { facts }) cfg
+    g.assign prf
 
 open Lean Elab Tactic Parser.Tactic
 

src/Lean/Elab/Tactic/Simp.lean

@@ -234,7 +234,7 @@ def elabSimpArgs (stx : Syntax) (ctx : Simp.Context) (simprocs : Simp.SimprocsAr
             logException ex
           else
             throw ex
-      return { ctx := { ctx with simpTheorems := thmsArray.set! 0 thms }, simprocs, starArg }
+      return { ctx := ctx.setSimpTheorems (thmsArray.set! 0 thms), simprocs, starArg }
     -- If recovery is disabled, then we want simp argument elaboration failures to be exceptions.
     -- This affects `addSimpTheorem`.
     if (← read).recover then
@@ -311,10 +311,11 @@ def mkSimpContext (stx : Syntax) (eraseLocal : Bool) (kind := SimpKind.simp)
     simpTheorems
   let simprocs ← if simpOnly then pure {} else Simp.getSimprocs
   let congrTheorems ← getSimpCongrTheorems
-  let r ← elabSimpArgs stx[4] (eraseLocal := eraseLocal) (kind := kind) (simprocs := #[simprocs]) {
-    config      := (← elabSimpConfig stx[1] (kind := kind))
-    simpTheorems := #[simpTheorems], congrTheorems
-  }
+  let ctx ← Simp.mkContext
+     (config := (← elabSimpConfig stx[1] (kind := kind)))
+     (simpTheorems := #[simpTheorems])
+     congrTheorems
+  let r ← elabSimpArgs stx[4] (eraseLocal := eraseLocal) (kind := kind) (simprocs := #[simprocs]) ctx
   if !r.starArg || ignoreStarArg then
     return { r with dischargeWrapper }
   else
@@ -329,7 +330,7 @@ def mkSimpContext (stx : Syntax) (eraseLocal : Bool) (kind := SimpKind.simp)
     for h in hs do
       unless simpTheorems.isErased (.fvar h) do
         simpTheorems ← simpTheorems.addTheorem (.fvar h) (← h.getDecl).toExpr
-    let ctx := { ctx with simpTheorems }
+    let ctx := ctx.setSimpTheorems simpTheorems
     return { ctx, simprocs, dischargeWrapper }
 
 register_builtin_option tactic.simp.trace : Bool := {

src/Lean/Elab/Tactic/Simpa.lean

@@ -36,9 +36,9 @@ deriving instance Repr for UseImplicitLambdaResult
     let stx ← `(tactic| simp $cfg:optConfig $(disch)? $[only%$only]? $[[$args,*]]?)
     let { ctx, simprocs, dischargeWrapper } ←
       withMainContext <| mkSimpContext stx (eraseLocal := false)
-    let ctx := if unfold.isSome then { ctx with config.autoUnfold := true } else ctx
+    let ctx := if unfold.isSome then ctx.setAutoUnfold else ctx
     -- TODO: have `simpa` fail if it doesn't use `simp`.
-    let ctx := { ctx with config := { ctx.config with failIfUnchanged := false } }
+    let ctx := ctx.setFailIfUnchanged false
     dischargeWrapper.with fun discharge? => do
       let (some (_, g), stats) ← simpGoal (← getMainGoal) ctx (simprocs := simprocs)
           (simplifyTarget := true) (discharge? := discharge?)

src/Lean/Message.lean

@@ -116,7 +116,7 @@ variable (p : Name → Bool) in
 /-- Returns true when the message contains a `MessageData.tagged tag ..` constructor where `p tag`
 is true.
 
-This does not descend into lazily generated subtress (`.ofLazy`); message tags
+This does not descend into lazily generated subtrees (`.ofLazy`); message tags
 of interest (like those added by `logLinter`) are expected to be near the root
 of the `MessageData`, and not hidden inside `.ofLazy`.
 -/
@@ -130,6 +130,19 @@ partial def hasTag : MessageData → Bool
   | trace data msg msgs     => p data.cls || hasTag msg || msgs.any hasTag
   | _                       => false
 
+/--
+Returns the top-level tag of the message.
+If none, returns `Name.anonymous`.
+
+This does not descend into message subtrees (e.g., `.compose`, `.ofLazy`).
+The message kind is expected to describe the whole message.
+-/
+def kind : MessageData → Name
+  | withContext _ msg       => kind msg
+  | withNamingContext _ msg => kind msg
+  | tagged n _              => n
+  | _                       => .anonymous
+
 /-- An empty message. -/
 def nil : MessageData :=
   ofFormat Format.nil
@@ -315,7 +328,7 @@ structure BaseMessage (α : Type u) where
   endPos        : Option Position := none
   /-- If `true`, report range as given; see `msgToInteractiveDiagnostic`. -/
   keepFullRange : Bool := false
-  severity      : MessageSeverity := MessageSeverity.error
+  severity      : MessageSeverity := .error
   caption       : String          := ""
   /-- The content of the message. -/
   data          : α
@@ -328,7 +341,10 @@ abbrev Message := BaseMessage MessageData
 /-- A `SerialMessage` is a `Message` whose `MessageData` has been eagerly
 serialized and is thus appropriate for use in pure contexts where the effectful
 `MessageData.toString` cannot be used. -/
-abbrev SerialMessage := BaseMessage String
+structure SerialMessage extends BaseMessage String where
+  /-- The message kind (i.e., the top-level tag). -/
+  kind          : Name
+  deriving ToJson, FromJson
 
 namespace SerialMessage
 
@@ -354,8 +370,12 @@ end SerialMessage
 
 namespace Message
 
+@[inherit_doc MessageData.kind] abbrev kind (msg : Message) :=
+  msg.data.kind
+
+/-- Serializes the message, converting its data into a string and saving its kind. -/
 @[inline] def serialize (msg : Message) : IO SerialMessage := do
-  return {msg with data := ← msg.data.toString}
+  return {msg with kind := msg.kind, data := ← msg.data.toString}
 
 protected def toString (msg : Message) (includeEndPos := false) : IO String := do
   -- Remark: The inline here avoids a new message allocation when `msg` is shared

src/Lean/Meta/Basic.lean

@@ -332,7 +332,7 @@ register_builtin_option maxSynthPendingDepth : Nat := {
   Contextual information for the `MetaM` monad.
 -/
 structure Context where
-  config            : Config               := {}
+  private config    : Config               := {}
   /-- Local context -/
   lctx              : LocalContext         := {}
   /-- Local instances in `lctx`. -/
@@ -943,6 +943,15 @@ def elimMVarDeps (xs : Array Expr) (e : Expr) (preserveOrder : Bool := false) :
 @[inline] def withConfig (f : Config → Config) : n α → n α :=
   mapMetaM <| withReader (fun ctx => { ctx with config := f ctx.config })
 
+@[inline] def withCanUnfoldPred (p : Config → ConstantInfo → CoreM Bool) : n α → n α :=
+  mapMetaM <| withReader (fun ctx => { ctx with canUnfold? := p })
+
+@[inline] def withIncSynthPending : n α → n α :=
+  mapMetaM <| withReader (fun ctx => { ctx with synthPendingDepth := ctx.synthPendingDepth + 1 })
+
+@[inline] def withInTypeClassResolution : n α → n α :=
+  mapMetaM <| withReader (fun ctx => { ctx with inTypeClassResolution := true })
+
 /--
 Executes `x` tracking zetaDelta reductions `Config.trackZetaDelta := true`
 -/
@@ -1422,6 +1431,14 @@ def withLocalDecl (name : Name) (bi : BinderInfo) (type : Expr) (k : Expr → n
 def withLocalDeclD (name : Name) (type : Expr) (k : Expr → n α) : n α :=
   withLocalDecl name BinderInfo.default type k
 
+/--
+Similar to `withLocalDecl`, but it does **not** check whether the new variable is a local instance or not.
+-/
+def withLocalDeclNoLocalInstanceUpdate (name : Name) (bi : BinderInfo) (type : Expr) (x : Expr → MetaM α) : MetaM α := do
+  let fvarId ← mkFreshFVarId
+  withReader (fun ctx => { ctx with lctx := ctx.lctx.mkLocalDecl fvarId name type bi }) do
+    x (mkFVar fvarId)
+
 /-- Append an array of free variables `xs` to the local context and execute `k xs`.
 `declInfos` takes the form of an array consisting of:
 - the name of the variable
@@ -1538,11 +1555,11 @@ def withReplaceFVarId {α} (fvarId : FVarId) (e : Expr) : MetaM α → MetaM α
     localInstances := ctx.localInstances.erase fvarId }
 
 /--
-  `withNewMCtxDepth k` executes `k` with a higher metavariable context depth,
-  where metavariables created outside the `withNewMCtxDepth` (with a lower depth) cannot be assigned.
-  If `allowLevelAssignments` is set to true, then the level metavariable depth
-  is not increased, and level metavariables from the outer scope can be
-  assigned.  (This is used by TC synthesis.)
+`withNewMCtxDepth k` executes `k` with a higher metavariable context depth,
+where metavariables created outside the `withNewMCtxDepth` (with a lower depth) cannot be assigned.
+If `allowLevelAssignments` is set to true, then the level metavariable depth
+is not increased, and level metavariables from the outer scope can be
+assigned.  (This is used by TC synthesis.)
 -/
 def withNewMCtxDepth (k : n α) (allowLevelAssignments := false) : n α :=
   mapMetaM (withNewMCtxDepthImp allowLevelAssignments) k
@@ -1552,13 +1569,20 @@ private def withLocalContextImp (lctx : LocalContext) (localInsts : LocalInstanc
     x
 
 /--
-  `withLCtx lctx localInsts k` replaces the local context and local instances, and then executes `k`.
-  The local context and instances are restored after executing `k`.
-  This method assumes that the local instances in `localInsts` are in the local context `lctx`.
+`withLCtx lctx localInsts k` replaces the local context and local instances, and then executes `k`.
+The local context and instances are restored after executing `k`.
+This method assumes that the local instances in `localInsts` are in the local context `lctx`.
 -/
 def withLCtx (lctx : LocalContext) (localInsts : LocalInstances) : n α → n α :=
   mapMetaM <| withLocalContextImp lctx localInsts
 
+/--
+Simpler version of `withLCtx` which just updates the local context. It is the resposability of the
+caller ensure the local instances are also properly updated.
+-/
+def withLCtx' (lctx : LocalContext) : n α → n α :=
+  mapMetaM <| withReader (fun ctx => { ctx with lctx })
+
 /--
 Runs `k` in a local environment with the `fvarIds` erased.
 -/

src/Lean/Meta/Coe.lean

@@ -157,9 +157,11 @@ def coerceMonadLift? (e expectedType : Expr) : MetaM (Option Expr) := do
   let eType ← instantiateMVars (← inferType e)
   let some (n, β) ← isTypeApp? expectedType | return none
   let some (m, α) ← isTypeApp? eType | return none
+  -- Need to save and restore the state in case `m` and `n` are defeq but not monads to prevent this procedure from having side effects.
+  let saved ← saveState
   if (← isDefEq m n) then
-    let some monadInst ← isMonad? n | return none
-    try expandCoe (← mkAppOptM ``Lean.Internal.coeM #[m, α, β, none, monadInst, e]) catch _ => return none
+    let some monadInst ← isMonad? n | restoreState saved; return none
+    try expandCoe (← mkAppOptM ``Lean.Internal.coeM #[m, α, β, none, monadInst, e]) catch _ => restoreState saved; return none
   else if autoLift.get (← getOptions) then
     try
       -- Construct lift from `m` to `n`

src/Lean/Meta/DiscrTree.lean

@@ -553,8 +553,8 @@ private def getKeyArgs (e : Expr) (isMatch root : Bool) (config : WhnfCoreConfig
     if isMatch then
       return (.other, #[])
     else do
-      let ctx ← read
-      if ctx.config.isDefEqStuckEx then
+      let cfg ← getConfig
+      if cfg.isDefEqStuckEx then
         /-
           When the configuration flag `isDefEqStuckEx` is set to true,
           we want `isDefEq` to throw an exception whenever it tries to assign

src/Lean/Meta/ExprDefEq.lean

@@ -364,7 +364,7 @@ private partial def isDefEqBindingAux (lctx : LocalContext) (fvars : Array Expr)
   | Expr.forallE n d₁ b₁ _, Expr.forallE _ d₂ b₂ _ => process n d₁ d₂ b₁ b₂
   | Expr.lam     n d₁ b₁ _, Expr.lam     _ d₂ b₂ _ => process n d₁ d₂ b₁ b₂
   | _,                      _                      =>
-    withReader (fun ctx => { ctx with lctx := lctx }) do
+    withLCtx' lctx do
       isDefEqBindingDomain fvars ds₂ do
         Meta.isExprDefEqAux (e₁.instantiateRev fvars) (e₂.instantiateRev fvars)
 
@@ -758,8 +758,8 @@ mutual
     if mvarDecl.depth != (← getMCtx).depth || mvarDecl.kind.isSyntheticOpaque then
       traceM `Meta.isDefEq.assign.readOnlyMVarWithBiggerLCtx <| addAssignmentInfo (mkMVar mvarId)
       throwCheckAssignmentFailure
-    let ctxMeta ← readThe Meta.Context
-    unless ctxMeta.config.ctxApprox && ctx.mvarDecl.lctx.isSubPrefixOf mvarDecl.lctx do
+    let cfg ← getConfig
+    unless cfg.ctxApprox && ctx.mvarDecl.lctx.isSubPrefixOf mvarDecl.lctx do
       traceM `Meta.isDefEq.assign.readOnlyMVarWithBiggerLCtx <| addAssignmentInfo (mkMVar mvarId)
       throwCheckAssignmentFailure
     /- Create an auxiliary metavariable with a smaller context and "checked" type.
@@ -814,8 +814,8 @@ mutual
 
   partial def checkApp (e : Expr) : CheckAssignmentM Expr :=
     e.withApp fun f args => do
-      let ctxMeta ← readThe Meta.Context
-      if f.isMVar && ctxMeta.config.ctxApprox && args.all Expr.isFVar then
+      let cfg ← getConfig
+      if f.isMVar && cfg.ctxApprox && args.all Expr.isFVar then
         let f ← check f
         catchInternalId outOfScopeExceptionId
           (do
@@ -1794,8 +1794,8 @@ private partial def isDefEqQuickOther (t s : Expr) : MetaM LBool := do
         | LBool.true => return LBool.true
         | LBool.false => return LBool.false
         | _ =>
-          let ctx ← read
-          if ctx.config.isDefEqStuckEx then do
+          let cfg ← getConfig
+          if cfg.isDefEqStuckEx then do
             trace[Meta.isDefEq.stuck] "{t} =?= {s}"
             Meta.throwIsDefEqStuck
           else
@@ -1834,7 +1834,7 @@ end
       let e ← instantiateMVars e
       successK e
     else
-      if (← read).config.isDefEqStuckEx then
+      if (← getConfig).isDefEqStuckEx then
         /-
         When `isDefEqStuckEx := true` and `mvar` was created in a previous level,
         we should throw an exception. See issue #2736 for a situation where this can happen.

src/Lean/Meta/GetUnfoldableConst.lean

@@ -22,10 +22,11 @@ private def canUnfoldDefault (cfg : Config) (info : ConstantInfo) : CoreM Bool :
 
 def canUnfold (info : ConstantInfo) : MetaM Bool := do
   let ctx ← read
+  let cfg ← getConfig
   if let some f := ctx.canUnfold? then
-    f ctx.config info
+    f cfg info
   else
-    canUnfoldDefault ctx.config info
+    canUnfoldDefault cfg info
 
 /--
 Look up a constant name, returning the `ConstantInfo`

src/Lean/Meta/InferType.lean

@@ -382,11 +382,6 @@ def isType (e : Expr) : MetaM Bool := do
     | .sort .. => return true
     | _        => return false
 
-@[inline] private def withLocalDecl' {α} (name : Name) (bi : BinderInfo) (type : Expr) (x : Expr → MetaM α) : MetaM α := do
-  let fvarId ← mkFreshFVarId
-  withReader (fun ctx => { ctx with lctx := ctx.lctx.mkLocalDecl fvarId name type bi }) do
-    x (mkFVar fvarId)
-
 def typeFormerTypeLevelQuick : Expr → Option Level
   | .forallE _ _ b _ => typeFormerTypeLevelQuick b
   | .sort l => some l
@@ -403,7 +398,7 @@ where
   go (type : Expr) (xs : Array Expr) : MetaM (Option Level) := do
     match type with
     | .sort l => return some l
-    | .forallE n d b c => withLocalDecl' n c (d.instantiateRev xs) fun x => go b (xs.push x)
+    | .forallE n d b c => withLocalDeclNoLocalInstanceUpdate n c (d.instantiateRev xs) fun x => go b (xs.push x)
     | _ =>
       let type ← whnfD (type.instantiateRev xs)
       match type with

src/Lean/Meta/LazyDiscrTree.lean

@@ -222,8 +222,8 @@ private def getKeyArgs (e : Expr) (isMatch root : Bool) (config : WhnfCoreConfig
     if isMatch then
       return (.other, #[])
     else do
-      let ctx ← read
-      if ctx.config.isDefEqStuckEx then
+      let cfg ← getConfig
+      if cfg.isDefEqStuckEx then
         /-
           When the configuration flag `isDefEqStuckEx` is set to true,
           we want `isDefEq` to throw an exception whenever it tries to assign

src/Lean/Meta/LevelDefEq.lean

@@ -149,8 +149,8 @@ mutual
             if r != LBool.undef then
               return r == LBool.true
             else if !(← hasAssignableLevelMVar lhs <||> hasAssignableLevelMVar rhs) then
-              let ctx ← read
-              if ctx.config.isDefEqStuckEx && (lhs.isMVar || rhs.isMVar) then do
+              let cfg ← getConfig
+              if cfg.isDefEqStuckEx && (lhs.isMVar || rhs.isMVar) then do
                 trace[Meta.isLevelDefEq.stuck] "{lhs} =?= {rhs}"
                 Meta.throwIsDefEqStuck
               else

src/Lean/Meta/Match/MatcherApp/Transform.lean

@@ -162,7 +162,7 @@ def refineThrough? (matcherApp : MatcherApp) (e : Expr) :
 private def withUserNamesImpl {α} (fvars : Array Expr) (names : Array Name) (k : MetaM α) : MetaM α := do
   let lctx := (Array.zip fvars names).foldl (init := ← (getLCtx)) fun lctx (fvar, name) =>
     lctx.setUserName fvar.fvarId! name
-  withTheReader Meta.Context (fun ctx => { ctx with lctx }) k
+  withLCtx' lctx k
 
 /--
 Sets the user name of the FVars in the local context according to the given array of names.

src/Lean/Meta/SynthInstance.lean

@@ -782,7 +782,7 @@ def synthInstance? (type : Expr) (maxResultSize? : Option Nat := none) : MetaM (
     (return m!"{exceptOptionEmoji ·} {← instantiateMVars type}") do
   withConfig (fun config => { config with isDefEqStuckEx := true, transparency := TransparencyMode.instances,
                                           foApprox := true, ctxApprox := true, constApprox := false, univApprox := false }) do
-  withReader (fun ctx => { ctx with inTypeClassResolution := true }) do
+  withInTypeClassResolution do
     let localInsts ← getLocalInstances
     let type ← instantiateMVars type
     let type ← preprocess type
@@ -839,7 +839,7 @@ private def synthPendingImp (mvarId : MVarId) : MetaM Bool := withIncRecDepth <|
         recordSynthPendingFailure mvarDecl.type
         return false
       else
-        withReader (fun ctx => { ctx with synthPendingDepth := ctx.synthPendingDepth + 1 }) do
+        withIncSynthPending do
           trace[Meta.synthPending] "synthPending {mkMVar mvarId}"
           let val? ← catchInternalId isDefEqStuckExceptionId (synthInstance? mvarDecl.type (maxResultSize? := none)) (fun _ => pure none)
           match val? with

src/Lean/Meta/Tactic/AC/Main.lean

@@ -188,12 +188,10 @@ def post (e : Expr) : SimpM Simp.Step := do
   | e, _ => return Simp.Step.done { expr := e }
 
 def rewriteUnnormalized (mvarId : MVarId) : MetaM MVarId := do
-  let simpCtx :=
-    {
-      simpTheorems  := {}
-      congrTheorems := (← getSimpCongrTheorems)
-      config        := Simp.neutralConfig
-    }
+  let simpCtx ← Simp.mkContext
+      (simpTheorems  := {})
+      (congrTheorems := (← getSimpCongrTheorems))
+      (config        := Simp.neutralConfig)
   let tgt ← instantiateMVars (← mvarId.getType)
   let (res, _) ← Simp.main tgt simpCtx (methods := { post })
   applySimpResultToTarget mvarId tgt res
@@ -207,12 +205,10 @@ def rewriteUnnormalizedRefl (goal : MVarId) : MetaM Unit := do
 
 def acNfHypMeta (goal : MVarId) (fvarId : FVarId) : MetaM (Option MVarId) := do
   goal.withContext do
-    let simpCtx :=
-    {
-      simpTheorems  := {}
-      congrTheorems := (← getSimpCongrTheorems)
-      config        := Simp.neutralConfig
-    }
+    let simpCtx ← Simp.mkContext
+      (simpTheorems  := {})
+      (congrTheorems := (← getSimpCongrTheorems))
+      (config        := Simp.neutralConfig)
     let tgt ← instantiateMVars (← fvarId.getType)
     let (res, _) ← Simp.main tgt simpCtx (methods := { post })
     return (← applySimpResultToLocalDecl goal fvarId res false).map (·.snd)

src/Lean/Meta/Tactic/Acyclic.lean

@@ -38,7 +38,10 @@ where
       let sizeOfEq ← mkLT sizeOf_lhs sizeOf_rhs
       let hlt ← mkFreshExprSyntheticOpaqueMVar sizeOfEq
       -- TODO: we only need the `sizeOf` simp theorems
-      match (← simpTarget hlt.mvarId! { config.arith := true, simpTheorems := #[ (← getSimpTheorems) ] } {}).1 with
+      let ctx ← Simp.mkContext
+         (config := { arith := true })
+         (simpTheorems := #[ (← getSimpTheorems) ])
+      match (← simpTarget hlt.mvarId! ctx {}).1 with
       | some _ => return false
       | none   =>
         let heq ← mkCongrArg sizeOf_lhs.appFn! (← mkEqSymm h)

src/Lean/Meta/Tactic/Apply.lean

@@ -254,10 +254,6 @@ Apply `And.intro` as much as possible to goal `mvarId`.
 abbrev splitAnd (mvarId : MVarId) : MetaM (List MVarId) :=
   splitAndCore mvarId
 
-@[deprecated splitAnd (since := "2024-03-17")]
-def _root_.Lean.Meta.splitAnd (mvarId : MVarId) : MetaM (List MVarId) :=
-  mvarId.splitAnd
-
 def exfalso (mvarId : MVarId) : MetaM MVarId :=
   mvarId.withContext do
     mvarId.checkNotAssigned `exfalso

src/Lean/Meta/Tactic/Grind/Preprocessor.lean

@@ -38,11 +38,10 @@ abbrev PreM := ReaderT Context $ StateRefT State GrindM
 def PreM.run (x : PreM α) : GrindM α := do
   let thms ← grindNormExt.getTheorems
   let simprocs := #[(← grindNormSimprocExt.getSimprocs)]
-  let simp : Simp.Context := {
-    config := { arith := true }
-    simpTheorems := #[thms]
-    congrTheorems := (← getSimpCongrTheorems)
-  }
+  let simp ← Simp.mkContext
+    (config := { arith := true })
+    (simpTheorems := #[thms])
+    (congrTheorems := (← getSimpCongrTheorems))
   x { simp, simprocs } |>.run' {}
 
 def simp (_goal : Goal) (e : Expr) : PreM Simp.Result := do

src/Lean/Meta/Tactic/Intro.lean

@@ -17,7 +17,7 @@ namespace Lean.Meta
     match i, type with
     | 0, type =>
       let type := type.instantiateRevRange j fvars.size fvars
-      withReader (fun ctx => { ctx with lctx := lctx }) do
+      withLCtx' lctx do
         withNewLocalInstances fvars j do
           let tag     ← mvarId.getTag
           let type := type.headBeta
@@ -57,7 +57,7 @@ namespace Lean.Meta
         loop i lctx fvars j s body
       else
         let type := type.instantiateRevRange j fvars.size fvars
-        withReader (fun ctx => { ctx with lctx := lctx }) do
+        withLCtx' lctx do
           withNewLocalInstances fvars j do
             /- We used to use just `whnf`, but it produces counterintuitive behavior if
               - `type` is a metavariable `?m` such that `?m := let x := v; b`, or

src/Lean/Meta/Tactic/Rewrites.lean

@@ -60,9 +60,6 @@ private def addImport (name : Name) (constInfo : ConstantInfo) :
         pure a
       | _ => return #[]
 
-/-- Configuration for `DiscrTree`. -/
-def discrTreeConfig : WhnfCoreConfig := {}
-
 /-- Select `=` and `↔` local hypotheses. -/
 def localHypotheses (except : List FVarId := []) : MetaM (Array (Expr × Bool × Nat)) := do
   let r ← getLocalHyps

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

@@ -73,7 +73,10 @@ def getSimpTheorems : CoreM SimpTheorems :=
 def getSEvalTheorems : CoreM SimpTheorems :=
   sevalSimpExtension.getTheorems
 
-def Simp.Context.mkDefault : MetaM Context :=
-  return { config := {}, simpTheorems := #[(← Meta.getSimpTheorems)], congrTheorems := (← Meta.getSimpCongrTheorems) }
+def Simp.Context.mkDefault : MetaM Context := do
+  mkContext
+    (config := {})
+    (simpTheorems := #[(← Meta.getSimpTheorems)])
+    (congrTheorems := (← Meta.getSimpCongrTheorems))
 
 end Lean.Meta

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

@@ -20,18 +20,6 @@ builtin_initialize congrHypothesisExceptionId : InternalExceptionId ←
 def throwCongrHypothesisFailed : MetaM α :=
   throw <| Exception.internal congrHypothesisExceptionId
 
-/--
-  Helper method for bootstrapping purposes. It disables `arith` if support theorems have not been defined yet.
--/
-def Config.updateArith (c : Config) : CoreM Config := do
-  if c.arith then
-    if (← getEnv).contains ``Nat.Linear.ExprCnstr.eq_of_toNormPoly_eq then
-      return c
-    else
-      return { c with arith := false }
-  else
-    return c
-
 /-- Return true if `e` is of the form `ofNat n` where `n` is a kernel Nat literal -/
 def isOfNatNatLit (e : Expr) : Bool :=
   e.isAppOf ``OfNat.ofNat && e.getAppNumArgs >= 3 && (e.getArg! 1).isRawNatLit
@@ -256,7 +244,7 @@ def withNewLemmas {α} (xs : Array Expr) (f : SimpM α) : SimpM α := do
           s ← s.addTheorem (.fvar x.fvarId!) x
           updated := true
       if updated then
-        withTheReader Context (fun ctx => { ctx with simpTheorems := s }) f
+        withSimpTheorems s f
       else
         f
   else if (← getMethods).wellBehavedDischarge then
@@ -463,7 +451,7 @@ private partial def dsimpImpl (e : Expr) : SimpM Expr := do
   let m ← getMethods
   let pre := m.dpre >> doNotVisitOfNat >> doNotVisitOfScientific >> doNotVisitCharLit
   let post := m.dpost >> dsimpReduce
-  withTheReader Simp.Context (fun ctx => { ctx with inDSimp := true }) do
+  withInDSimp do
   transform (usedLetOnly := cfg.zeta) e (pre := pre) (post := post)
 
 def visitFn (e : Expr) : SimpM Result := do
@@ -658,11 +646,12 @@ where
     trace[Meta.Tactic.simp.heads] "{repr e.toHeadIndex}"
     simpLoop e
 
+-- TODO: delete
 @[inline] def withSimpContext (ctx : Context) (x : MetaM α) : MetaM α :=
   withConfig (fun c => { c with etaStruct := ctx.config.etaStruct }) <| withReducible x
 
 def main (e : Expr) (ctx : Context) (stats : Stats := {}) (methods : Methods := {}) : MetaM (Result × Stats) := do
-  let ctx := { ctx with config := (← ctx.config.updateArith), lctxInitIndices := (← getLCtx).numIndices }
+  let ctx ← ctx.setLctxInitIndices
   withSimpContext ctx do
     let (r, s) ← go e methods.toMethodsRef ctx |>.run { stats with }
     trace[Meta.Tactic.simp.numSteps] "{s.numSteps}"
@@ -810,7 +799,7 @@ def simpGoal (mvarId : MVarId) (ctx : Simp.Context) (simprocs : SimprocsArray :=
     for fvarId in fvarIdsToSimp do
       let localDecl ← fvarId.getDecl
       let type ← instantiateMVars localDecl.type
-      let ctx := { ctx with simpTheorems := ctx.simpTheorems.eraseTheorem (.fvar localDecl.fvarId) }
+      let ctx := ctx.setSimpTheorems <| ctx.simpTheorems.eraseTheorem (.fvar localDecl.fvarId)
       let (r, stats') ← simp type ctx simprocs discharge? stats
       stats := stats'
       match r.proof? with
@@ -844,7 +833,7 @@ def simpTargetStar (mvarId : MVarId) (ctx : Simp.Context) (simprocs : SimprocsAr
     let localDecl ← h.getDecl
     let proof  := localDecl.toExpr
     let simpTheorems ← ctx.simpTheorems.addTheorem (.fvar h) proof
-    ctx := { ctx with simpTheorems }
+    ctx := ctx.setSimpTheorems simpTheorems
   match (← simpTarget mvarId ctx simprocs discharge? (stats := stats)) with
   | (none, stats) => return (TacticResultCNM.closed, stats)
   | (some mvarId', stats') =>

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

@@ -41,7 +41,7 @@ def discharge?' (thmId : Origin) (x : Expr) (type : Expr) : SimpM Bool := do
     let ctx ← getContext
     if ctx.dischargeDepth >= ctx.maxDischargeDepth then
       return .maxDepth
-    else withTheReader Context (fun ctx => { ctx with dischargeDepth := ctx.dischargeDepth + 1 }) do
+    else withIncDischargeDepth do
       -- We save the state, so that `UsedTheorems` does not accumulate
       -- `simp` lemmas used during unsuccessful discharging.
       -- We use `withPreservedCache` to ensure the cache is restored after `discharge?`
@@ -446,10 +446,13 @@ def mkSEvalMethods : CoreM Methods := do
     wellBehavedDischarge := true
   }
 
-def mkSEvalContext : CoreM Context := do
+def mkSEvalContext : MetaM Context := do
   let s ← getSEvalTheorems
   let c ← Meta.getSimpCongrTheorems
-  return { simpTheorems := #[s], congrTheorems := c, config := { ground := true } }
+  mkContext
+    (simpTheorems := #[s])
+    (congrTheorems := c)
+    (config := { ground := true })
 
 /--
 Invoke ground/symbolic evaluator from `simp`.
@@ -552,7 +555,7 @@ private def dischargeUsingAssumption? (e : Expr) : SimpM (Option Expr) := do
 partial def dischargeEqnThmHypothesis? (e : Expr) : MetaM (Option Expr) := do
   assert! isEqnThmHypothesis e
   let mvar ← mkFreshExprSyntheticOpaqueMVar e
-  withReader (fun ctx => { ctx with canUnfold? := canUnfoldAtMatcher }) do
+  withCanUnfoldPred canUnfoldAtMatcher do
     if let .none ← go? mvar.mvarId! then
       instantiateMVars mvar
     else

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

@@ -43,7 +43,7 @@ private def initEntries : M Unit := do
       let localDecl ← h.getDecl
       let proof  := localDecl.toExpr
       simpThms ← simpThms.addTheorem (.fvar h) proof
-      modify fun s => { s with ctx.simpTheorems := simpThms }
+      modify fun s => { s with ctx := s.ctx.setSimpTheorems simpThms }
       if hsNonDeps.contains h then
         -- We only simplify nondependent hypotheses
         let type ← instantiateMVars localDecl.type
@@ -62,7 +62,7 @@ private partial def loop : M Bool := do
     let ctx := (← get).ctx
     -- We disable the current entry to prevent it to be simplified to `True`
     let simpThmsWithoutEntry := (← getSimpTheorems).eraseTheorem entry.id
-    let ctx := { ctx with simpTheorems := simpThmsWithoutEntry }
+    let ctx := ctx.setSimpTheorems simpThmsWithoutEntry
     let (r, stats) ← simpStep (← get).mvarId entry.proof entry.type ctx simprocs (stats := { (← get) with })
     modify fun s => { s with usedTheorems := stats.usedTheorems, diag := stats.diag }
     match r with
@@ -98,7 +98,7 @@ private partial def loop : M Bool := do
         simpThmsNew ← simpThmsNew.addTheorem (.other idNew) (← mkExpectedTypeHint proofNew typeNew)
         modify fun s => { s with
           modified         := true
-          ctx.simpTheorems := simpThmsNew
+          ctx              := ctx.setSimpTheorems simpThmsNew
           entries[i]       := { entry with type := typeNew, proof := proofNew, id := .other idNew }
         }
   -- simplify target

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

@@ -52,6 +52,7 @@ abbrev Cache := SExprMap Result
 abbrev CongrCache := ExprMap (Option CongrTheorem)
 
 structure Context where
+  private mk ::
   config           : Config := {}
   /-- `maxDischargeDepth` from `config` as an `UInt32`. -/
   maxDischargeDepth : UInt32 := UInt32.ofNatTruncate config.maxDischargeDepth
@@ -103,6 +104,41 @@ structure Context where
   inDSimp : Bool := false
   deriving Inhabited
 
+/--
+Helper method for bootstrapping purposes.
+It disables `arith` if support theorems have not been defined yet.
+-/
+private def updateArith (c : Config) : CoreM Config := do
+  if c.arith then
+    if (← getEnv).contains ``Nat.Linear.ExprCnstr.eq_of_toNormPoly_eq then
+      return c
+    else
+      return { c with arith := false }
+  else
+    return c
+
+def mkContext (config : Config := {}) (simpTheorems : SimpTheoremsArray := {}) (congrTheorems : SimpCongrTheorems := {}) : MetaM Context := do
+  let config ← updateArith config
+  return { config, simpTheorems, congrTheorems }
+
+def Context.setConfig (context : Context) (config : Config) : Context :=
+  { context with config }
+
+def Context.setSimpTheorems (c : Context) (simpTheorems : SimpTheoremsArray) : Context :=
+  { c with simpTheorems }
+
+def Context.setLctxInitIndices (c : Context) : MetaM Context :=
+  return { c with lctxInitIndices := (← getLCtx).numIndices }
+
+def Context.setAutoUnfold (c : Context) : Context :=
+  { c with config.autoUnfold := true }
+
+def Context.setFailIfUnchanged (c : Context) (flag : Bool) : Context :=
+  { c with config.failIfUnchanged := flag }
+
+def Context.setMemoize (c : Context) (flag : Bool) : Context :=
+  { c with config.memoize := flag }
+
 def Context.isDeclToUnfold (ctx : Context) (declName : Name) : Bool :=
   ctx.simpTheorems.isDeclToUnfold declName
 
@@ -158,6 +194,15 @@ instance : Nonempty MethodsRef := MethodsRefPointed.property
 
 abbrev SimpM := ReaderT MethodsRef $ ReaderT Context $ StateRefT State MetaM
 
+@[inline] def withIncDischargeDepth : SimpM α → SimpM α :=
+  withTheReader Context (fun ctx => { ctx with dischargeDepth := ctx.dischargeDepth + 1 })
+
+@[inline] def withSimpTheorems (s : SimpTheoremsArray) : SimpM α → SimpM α :=
+  withTheReader Context (fun ctx => { ctx with simpTheorems := s })
+
+@[inline] def withInDSimp : SimpM α → SimpM α :=
+  withTheReader Context (fun ctx => { ctx with inDSimp := true })
+
 @[extern "lean_simp"]
 opaque simp (e : Expr) : SimpM Result
 

src/Lean/Meta/Tactic/Split.lean

@@ -13,12 +13,11 @@ import Lean.Meta.Tactic.Generalize
 namespace Lean.Meta
 namespace Split
 
-def getSimpMatchContext : MetaM Simp.Context :=
-   return {
-      simpTheorems   := {}
-      congrTheorems := (← getSimpCongrTheorems)
-      config        := { Simp.neutralConfig with dsimp := false }
-   }
+def getSimpMatchContext : MetaM Simp.Context := do
+   Simp.mkContext
+      (simpTheorems   := {})
+      (congrTheorems := (← getSimpCongrTheorems))
+      (config        := { Simp.neutralConfig with dsimp := false })
 
 def simpMatch (e : Expr) : MetaM Simp.Result := do
   let discharge? ← SplitIf.mkDischarge?

src/Lean/Meta/Tactic/SplitIf.lean

@@ -19,11 +19,10 @@ def getSimpContext : MetaM Simp.Context := do
   s ← s.addConst ``if_neg
   s ← s.addConst ``dif_pos
   s ← s.addConst ``dif_neg
-  return {
-    simpTheorems  := #[s]
-    congrTheorems := (← getSimpCongrTheorems)
-    config        := { Simp.neutralConfig with dsimp := false }
-  }
+  Simp.mkContext
+    (simpTheorems  := #[s])
+    (congrTheorems := (← getSimpCongrTheorems))
+    (config        := { Simp.neutralConfig with dsimp := false })
 
 /--
   Default `discharge?` function for `simpIf` methods.

src/Lean/Meta/Tactic/Unfold.lean

@@ -10,11 +10,10 @@ import Lean.Meta.Tactic.Simp.Main
 
 namespace Lean.Meta
 
-private def getSimpUnfoldContext : MetaM Simp.Context :=
-   return {
-      congrTheorems := (← getSimpCongrTheorems)
-      config        := Simp.neutralConfig
-   }
+private def getSimpUnfoldContext : MetaM Simp.Context := do
+   Simp.mkContext
+      (congrTheorems := (← getSimpCongrTheorems))
+      (config        := Simp.neutralConfig)
 
 def unfold (e : Expr) (declName : Name) : MetaM Simp.Result := do
   if let some unfoldThm ← getUnfoldEqnFor? declName  then

src/Lean/Meta/UnificationHint.lean

@@ -96,7 +96,7 @@ builtin_initialize
 
 def tryUnificationHints (t s : Expr) : MetaM Bool := do
   trace[Meta.isDefEq.hint] "{t} =?= {s}"
-  unless (← read).config.unificationHints do
+  unless (← getConfig).unificationHints do
     return false
   if t.isMVar then
     return false

src/Lean/Meta/WHNF.lean

@@ -529,7 +529,7 @@ private def whnfMatcher (e : Expr) : MetaM Expr := do
      TODO: consider other solutions; investigate whether the solution above produces counterintuitive behavior.  -/
   if (← getTransparency) matches .instances | .reducible then
     -- Also unfold some default-reducible constants; see `canUnfoldAtMatcher`
-    withTransparency .instances <| withReader (fun ctx => { ctx with canUnfold? := canUnfoldAtMatcher }) do
+    withTransparency .instances <| withCanUnfoldPred canUnfoldAtMatcher do
       whnf e
   else
     -- Do NOT use `canUnfoldAtMatcher` here as it does not affect all/default reducibility and inhibits caching (#2564).

src/Lean/PrettyPrinter/Delaborator/TopDownAnalyze.lean

@@ -205,7 +205,7 @@ def replaceLPsWithVars (e : Expr) : MetaM Expr := do
     | l => if !l.hasParam then some l else none
 
 def isDefEqAssigning (t s : Expr) : MetaM Bool := do
-  withReader (fun ctx => { ctx with config := { ctx.config with assignSyntheticOpaque := true }}) $
+  withConfig (fun cfg => { cfg with assignSyntheticOpaque := true }) do
     Meta.isDefEq t s
 
 def checkpointDefEq (t s : Expr) : MetaM Bool := do
@@ -624,7 +624,7 @@ open TopDownAnalyze SubExpr
 def topDownAnalyze (e : Expr) : MetaM OptionsPerPos := do
   let s₀ ← get
   withTraceNode `pp.analyze (fun _ => return e) do
-    withReader (fun ctx => { ctx with config := Elab.Term.setElabConfig ctx.config }) do
+    withConfig Elab.Term.setElabConfig do
       let ϕ : AnalyzeM OptionsPerPos := do withNewMCtxDepth analyze; pure (← get).annotations
       try
         let knowsType := getPPAnalyzeKnowsType (← getOptions)

src/include/lean/lean.h

@@ -1617,7 +1617,16 @@ static inline uint8_t lean_int_dec_nonneg(b_lean_obj_arg a) {
 
 /* Bool */
 
-static inline uint64_t lean_bool_to_uint64(uint8_t a) { return ((uint64_t)a); }
+static inline uint8_t lean_bool_to_uint8(uint8_t a) { return a; }
+static inline uint16_t lean_bool_to_uint16(uint8_t a) { return (uint16_t)a; }
+static inline uint32_t lean_bool_to_uint32(uint8_t a) { return (uint32_t)a; }
+static inline uint64_t lean_bool_to_uint64(uint8_t a) { return (uint64_t)a; }
+static inline size_t lean_bool_to_usize(uint8_t a) { return (size_t)a; }
+static inline uint8_t lean_bool_to_int8(uint8_t a) { return (uint8_t)(int8_t)a; }
+static inline uint16_t lean_bool_to_int16(uint8_t a) { return (uint16_t)(int16_t)a; }
+static inline uint32_t lean_bool_to_int32(uint8_t a) { return (uint32_t)(int32_t)a; }
+static inline uint64_t lean_bool_to_int64(uint8_t a) { return (uint64_t)(int64_t)a; }
+static inline size_t lean_bool_to_isize(uint8_t a) { return (size_t)(ptrdiff_t)a; }
 
 
 /* UInt8 */

src/lake/Lake/CLI/Init.lean

@@ -24,12 +24,14 @@ s!"/{defaultLakeDir}
 "
 
 def basicFileContents :=
-  s!"def hello := \"world\""
+s!"def hello := \"world\"
+"
 
 def libRootFileContents (libName : String) (libRoot : Name) :=
 s!"-- This module serves as the root of the `{libName}` library.
 -- Import modules here that should be built as part of the library.
-import {libRoot}.Basic"
+import {libRoot}.Basic
+"
 
 def mainFileName : FilePath :=
   s!"{defaultExeRoot}.lean"

src/lake/Lake/CLI/Main.lean

@@ -515,7 +515,7 @@ protected def translateConfig : CliM PUnit := do
   if outFile?.isNone then
     IO.FS.rename pkg.configFile (pkg.configFile.addExtension "bak")
 
-def ReservoirConfig.currentSchemaVersion : StdVer := v!"1.0.0"
+def ReservoirConfig.currentSchemaVersion : StdVer := {major := 1}
 
 structure ReservoirConfig where
   name : String

src/lake/Lake/CLI/Translate/Lean.lean

@@ -119,7 +119,7 @@ def PackageConfig.mkSyntax (cfg : PackageConfig)
     |> addDeclFieldD `testDriverArgs cfg.testDriverArgs #[]
     |> addDeclFieldD `lintDriver lintDriver ""
     |> addDeclFieldD `lintDriverArgs cfg.lintDriverArgs #[]
-    |> addDeclFieldD `version cfg.version v!"0.0.0"
+    |> addDeclFieldD `version cfg.version {}
     |> addDeclField? `versionTags (quoteVerTags? cfg.versionTags)
     |> addDeclFieldD `description cfg.description ""
     |> addDeclFieldD `keywords cfg.keywords #[]

src/lake/Lake/CLI/Translate/Toml.lean

@@ -76,7 +76,7 @@ protected def PackageConfig.toToml (cfg : PackageConfig) (t : Table := {}) : Tab
   |>.smartInsert `releaseRepo (cfg.releaseRepo <|> cfg.releaseRepo?)
   |>.insertD `buildArchive (cfg.buildArchive?.getD cfg.buildArchive) (defaultBuildArchive cfg.name)
   |>.insertD `preferReleaseBuild cfg.preferReleaseBuild false
-  |>.insertD `version cfg.version v!"0.0.0"
+  |>.insertD `version cfg.version {}
   |> smartInsertVerTags cfg.versionTags
   |>.smartInsert `keywords cfg.description
   |>.smartInsert `keywords cfg.keywords

src/lake/Lake/Config/Package.lean

@@ -275,7 +275,7 @@ structure PackageConfig extends WorkspaceConfig, LeanConfig where
 
   Packages without a defined version default to `0.0.0`.
   -/
-  version : StdVer := v!"0.0.0"
+  version : StdVer := {}
 
   /--
   Git tags of this package's repository that should be treated as versions.

src/lake/Lake/Load/Manifest.lean

@@ -49,7 +49,7 @@ That is, Lake ignores the `-` suffix.
 - `"1.0.0"`: Switches to a semantic versioning scheme
 - `"1.1.0"`: Add optional `scope` package entry field
 -/
-@[inline] def Manifest.version : StdVer := v!"1.1.0"
+@[inline] def Manifest.version : StdVer := {major := 1, minor := 1}
 
 /-- Manifest version `0.6.0` package entry. For backwards compatibility. -/
 inductive PackageEntryV6
@@ -201,14 +201,14 @@ protected def fromJson? (json : Json) : Except String Manifest := do
   if ver.major > 1 then
     throw s!"manifest version '{ver}' is of a higher major version than this \
       Lake's '{Manifest.version}'; you may need to update your 'lean-toolchain'"
-  else if ver < v!"0.5.0" then
+  else if ver < {minor := 5} then
     throw s!"incompatible manifest version '{ver}'"
   else
     let name ← obj.getD "name" Name.anonymous
     let lakeDir ← obj.getD "lakeDir" defaultLakeDir
     let packagesDir? ← obj.get? "packagesDir"
     let packages ←
-      if ver < v!"0.7.0" then
+      if ver < {minor := 7} then
         (·.map PackageEntry.ofV6) <$> obj.getD "packages" #[]
       else
         obj.getD "packages" #[]

src/lake/Lake/Load/Toml.lean

@@ -207,7 +207,7 @@ protected def PackageConfig.decodeToml (t : Table) (ref := Syntax.missing) : Exc
   let testDriverArgs ← t.tryDecodeD `testDriverArgs #[]
   let lintDriver ← t.tryDecodeD `lintDriver ""
   let lintDriverArgs ← t.tryDecodeD `lintDriverArgs #[]
-  let version : StdVer ← t.tryDecodeD `version v!"0.0.0"
+  let version : StdVer ← t.tryDecodeD `version {}
   let versionTags ← optDecodeD defaultVersionTags (t.find? `versionTags)
     <| StrPat.decodeToml (presets := versionTagPresets)
   let description ← t.tryDecodeD `description ""

tests/bench/simp_arith1.lean

@@ -0,0 +1,29 @@
+import Lean
+
+open Lean Meta Elab in
+elab "largeGoal%" : term =>
+  let n := 30 -- number of variables
+  let r := 3 -- number of repetitions
+  let mkAdd := mkApp2 (mkConst ``Nat.add)
+  let mkMul := mkApp2 (mkConst ``Nat.mul)
+  let decls := Array.ofFn fun (i : Fin n) =>
+    ((`x).appendIndexAfter i, (fun _ => pure (mkConst ``Nat)))
+  withLocalDeclsD decls fun xs => do
+    let mut e₁ : Expr := mkNatLit 42
+    let mut e₂ : Expr := mkNatLit 23
+    for _ in [:r] do
+      for i in [:xs.size] do
+        e₁ := mkAdd (mkMul (mkNatLit i) e₁) xs[i]!
+        e₂ := mkAdd xs[i]! (mkMul e₂ (mkNatLit (xs.size - i)))
+    let goal ← mkEq e₁ e₂
+    let goal := mkNot goal
+    let goal ← mkForallFVars xs goal
+    return goal
+
+set_option maxRecDepth 10000
+
+-- manually verified: most time spent in type-checking
+-- set_option trace.profiler true
+example : largeGoal% := by
+  intros
+  simp_arith only

tests/bench/speedcenter.exec.velcom.yaml

@@ -316,6 +316,12 @@
   run_config:
     <<: *time
     cmd: lean reduceMatch.lean
+- attributes:
+    description: simp_arith1
+    tags: [fast, suite]
+  run_config:
+    <<: *time
+    cmd: lean simp_arith1.lean
 - attributes:
     description: nat_repr
     tags: [fast, suite]

tests/lean/1018unknowMVarIssue.lean.expected.out

@@ -56,8 +56,8 @@ a : α
           • Fam2.any : Fam2 α α @ ⟨9, 4⟩†-⟨9, 12⟩†
             • α : Type @ ⟨9, 4⟩†-⟨9, 12⟩†
           • a (isBinder := true) : α @ ⟨8, 2⟩†-⟨10, 19⟩†
-          • FVarAlias a: _uniq.632 -> _uniq.312
-          • FVarAlias α: _uniq.631 -> _uniq.310
+          • FVarAlias a: _uniq.585 -> _uniq.312
+          • FVarAlias α: _uniq.584 -> _uniq.310
           • ?m x α a : α @ ⟨9, 18⟩-⟨9, 19⟩ @ Lean.Elab.Term.elabHole
           • [.] Fam2.nat : none @ ⟨10, 4⟩-⟨10, 12⟩
           • Fam2.nat : Nat → Fam2 Nat Nat @ ⟨10, 4⟩-⟨10, 12⟩
@@ -71,8 +71,8 @@ a : α
           • Fam2.nat n : Fam2 Nat Nat @ ⟨10, 4⟩†-⟨10, 14⟩
             • n (isBinder := true) : Nat @ ⟨10, 13⟩-⟨10, 14⟩
           • a (isBinder := true) : Nat @ ⟨8, 2⟩†-⟨10, 19⟩†
-          • FVarAlias a: _uniq.663 -> _uniq.312
-          • FVarAlias n: _uniq.662 -> _uniq.310
+          • FVarAlias a: _uniq.616 -> _uniq.312
+          • FVarAlias n: _uniq.615 -> _uniq.310
           • n : Nat @ ⟨10, 18⟩-⟨10, 19⟩ @ Lean.Elab.Term.elabIdent
             • [.] n : some Nat @ ⟨10, 18⟩-⟨10, 19⟩
             • n : Nat @ ⟨10, 18⟩-⟨10, 19⟩

tests/lean/1081.lean.expected.out

@@ -1,12 +1,12 @@
 1081.lean:7:2-7:5: error: type mismatch
   rfl
 has type
-  f 0 y = f 0 y : Prop
+  ?m = ?m : Prop
 but is expected to have type
   f 0 y = y : Prop
 1081.lean:23:4-23:7: error: type mismatch
   rfl
 has type
-  insert a ⟨0, ⋯⟩ v = insert a ⟨0, ⋯⟩ v : Prop
+  ?m = ?m : Prop
 but is expected to have type
   insert a ⟨0, ⋯⟩ v = cons a v : Prop

tests/lean/1433.lean.expected.out

@@ -1,6 +1,6 @@
 1433.lean:11:49-11:52: error: type mismatch
   rfl
 has type
-  dividend % divisor = dividend % divisor : Prop
+  ?m = ?m : Prop
 but is expected to have type
   dividend % divisor = wrongRem : Prop

tests/lean/755.lean

@@ -1,3 +1,5 @@
+set_option pp.mvars false
+
 def Additive (α : Type) := α
 
 instance [OfNat α 1] : OfNat (Additive α) (nat_lit 0) := ⟨(1 : α)⟩

tests/lean/755.lean.expected.out

@@ -1,24 +1,24 @@
-755.lean:5:44-5:47: error: type mismatch
+755.lean:7:44-7:47: error: type mismatch
   rfl
 has type
-  0 = @OfNat.ofNat Nat 0 (instOfNatNat 0) : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
-  0 = @OfNat.ofNat (Additive Nat) 0 instOfNatAdditiveOfOfNatNat : Prop
-755.lean:24:2-24:5: error: type mismatch
+  0 = 0 : Prop
+755.lean:26:2-26:5: error: type mismatch
   rfl
 has type
-  2 * 3 = @HMul.hMul Nat Nat Nat instHMul 2 3 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
-  2 * 3 = @HMul.hMul (Foo Nat) (Foo Nat) (Foo Nat) instHMulFooOfHAdd 2 3 : Prop
-755.lean:27:2-27:5: error: type mismatch
+  2 * 3 = 2 * 3 : Prop
+755.lean:29:2-29:5: error: type mismatch
   rfl
 has type
-  2 + 3 = @HAdd.hAdd Nat Nat Nat instHAdd 2 3 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
-  2 + 3 = @HAdd.hAdd (Foo Nat) (Foo Nat) (Foo Nat) instHAddFoo 2 3 : Prop
-755.lean:30:2-30:5: error: type mismatch
+  2 + 3 = 2 + 3 : Prop
+755.lean:32:2-32:5: error: type mismatch
   rfl
 has type
-  2 - 3 = @HSub.hSub Nat Nat Nat instHSub 2 3 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
-  2 - 3 = @HSub.hSub (Foo Nat) (Foo Nat) (Foo Nat) instHSubFooOfHAdd 2 3 : Prop
+  2 - 3 = 2 - 3 : Prop

tests/lean/bool2int.lean

@@ -0,0 +1,20 @@
+#eval Bool.toUInt8 false = 0
+#eval Bool.toUInt8 true = 1
+#eval Bool.toUInt16 false = 0
+#eval Bool.toUInt16 true = 1
+#eval Bool.toUInt32 false = 0
+#eval Bool.toUInt32 true = 1
+#eval Bool.toUInt64 false = 0
+#eval Bool.toUInt64 true = 1
+#eval Bool.toUSize false = 0
+#eval Bool.toUSize true = 1
+#eval Bool.toInt8 false = 0
+#eval Bool.toInt8 true = 1
+#eval Bool.toInt16 false = 0
+#eval Bool.toInt16 true = 1
+#eval Bool.toInt32 false = 0
+#eval Bool.toInt32 true = 1
+#eval Bool.toInt64 false = 0
+#eval Bool.toInt64 true = 1
+#eval Bool.toISize false = 0
+#eval Bool.toISize true = 1

tests/lean/bool2int.lean.expected.out

@@ -0,0 +1,20 @@
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true
+true

tests/lean/calcErrors.lean.expected.out

@@ -1,7 +1,7 @@
 calcErrors.lean:7:30-7:33: error: type mismatch
   rfl
 has type
-  b + b = b + b : Prop
+  ?m = ?m : Prop
 but is expected to have type
   b + b = 0 + c + b : Prop
 calcErrors.lean:13:8-13:29: error: invalid 'calc' step, left-hand side is

tests/lean/coeM.lean

@@ -4,6 +4,8 @@
 The functions inserted for the coercions are supposed to be inlined immediately during elaboration.
 -/
 
+set_option pp.mvars false
+
 variable (p : Nat → Prop) (m : IO (Subtype p))
 
 /-!
@@ -15,3 +17,18 @@ variable (p : Nat → Prop) (m : IO (Subtype p))
 `Lean.Internal.coeM`
 -/
 #check (m : IO Nat)
+
+/-!
+Making sure the monad lift coercion elaborator does not have side effects.
+
+It used to be responsible for hinting that the LHSs of equalities were defeq, like in the following example.
+It was checking that `Eq (some true)` and `Eq _` were defeq monads. The defeq check caused `_` to be solved as `some true`.
+-/
+/--
+error: invalid dotted identifier notation, expected type is not of the form (... → C ...) where C is a constant
+  ?_
+-/
+#guard_msgs in
+example : some true = (some true).map id := by
+  refine show _ = .some true from ?_
+  rfl

tests/lean/etaStructIssue.lean.expected.out

@@ -1,6 +1,6 @@
 etaStructIssue.lean:20:2-20:5: error: type mismatch
   rfl
 has type
-  mkNat e x₁ = mkNat e x₁ : Prop
+  ?m = ?m : Prop
 but is expected to have type
   mkNat e x₁ = mkNat e.mk x₂ : Prop

tests/lean/interactive/builtinCodeactions.lean

@@ -0,0 +1,7 @@
+/-- Must not introduce line break between `at` and `h` -/
+example {a b c d : Nat} (h : a = b)
+    (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA : b = c)
+    (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa : c = d) :
+    a = b := by
+  simp? [AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA, aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa] at h
+  --^ codeAction

tests/lean/interactive/builtinCodeactions.lean.expected.out

@@ -0,0 +1,13 @@
+{"title":
+ "Try this: simp only [AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,\n    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa] at h",
+ "kind": "quickfix",
+ "isPreferred": true,
+ "edit":
+ {"documentChanges":
+  [{"textDocument": {"version": 1, "uri": "file:///builtinCodeactions.lean"},
+    "edits":
+    [{"range":
+      {"start": {"line": 5, "character": 2},
+       "end": {"line": 5, "character": 97}},
+      "newText":
+      "simp only [AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,\n    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa] at h"}]}]}}

tests/lean/isDefEqOffsetBug.lean.expected.out

@@ -1,6 +1,6 @@
 isDefEqOffsetBug.lean:19:2-19:5: error: type mismatch
   rfl
 has type
-  0 + 0 = 0 + 0 : Prop
+  ?m = ?m : Prop
 but is expected to have type
   0 + 0 = 0 : Prop

tests/lean/mulcommErrorMessage.lean.expected.out

@@ -8,16 +8,10 @@ the following variables have been introduced by the implicit lambda feature
   a✝ : Bool
   b✝ : Bool
 you can disable implicit lambdas using `@` or writing a lambda expression with `{}` or `[]` binder annotations.
-mulcommErrorMessage.lean:11:22-11:25: error: type mismatch
-  rfl
-has type
-  true = true : Prop
-but is expected to have type
-  true = false : Prop
 mulcommErrorMessage.lean:12:22-12:25: error: type mismatch
   rfl
 has type
-  false = false : Prop
+  ?m = ?m : Prop
 but is expected to have type
   false = true : Prop
 mulcommErrorMessage.lean:16:3-17:47: error: type mismatch

tests/lean/phashmap_inst_coherence.lean.expected.out

@@ -5,4 +5,4 @@ argument
 has type
   @PersistentHashMap Nat Nat instBEqOfDecidableEq instHashableNat : Type
 but is expected to have type
-  @PersistentHashMap Nat Nat instBEqOfDecidableEq natDiffHash : Type
+  @PersistentHashMap Nat Nat ?m natDiffHash : Type

tests/lean/run/1017.lean

@@ -25,7 +25,7 @@ def isFinite : Prop :=
 
 instance hasNextWF : WellFoundedRelation {s : ρ // isFinite s} where
   rel := λ s1 s2 => hasNext s2.val s1.val
-  wf := ⟨λ ⟨s,h⟩ => ⟨⟨s,h⟩, by
+  wf := ⟨λ ⟨s,h⟩ => ⟨Subtype.mk s h, by
     simp only [Subtype.forall]
     cases h; case intro w h =>
     induction w generalizing s

tests/lean/run/3150.lean

@@ -0,0 +1,24 @@
+class One (α : Type) where
+  one : α
+
+variable (R A : Type) [One R] [One A]
+
+class OneHom where
+  toFun : R → A
+  map_one : toFun One.one = One.one
+
+structure Subone where
+  mem : R → Prop
+  one_mem : mem One.one
+
+structure Subalgebra [OneHom R A] extends Subone A : Type where
+  algebraMap_mem : ∀ r : R, mem (OneHom.toFun r)
+  one_mem := OneHom.map_one (R := R) (A := A) ▸ algebraMap_mem One.one
+
+/--
+error: fields missing: 'one_mem'
+-/
+#guard_msgs in
+example [OneHom R A] : Subalgebra R A where
+  mem := _
+  algebraMap_mem := _

tests/lean/run/4405.lean

@@ -4,13 +4,13 @@ set_option pp.mvars false
 
 /--
 error: application type mismatch
-  ⟨Nat.lt_irrefl ↑(?_ n), Fin.is_lt (?_ n)⟩
+  ⟨Nat.lt_irrefl (?_ n), Fin.is_lt ?_⟩
 argument
-  Fin.is_lt (?_ n)
+  Fin.is_lt ?_
 has type
-  ↑(?_ n) < ?_ n : Prop
+  ↑?_ < ?_ : Prop
 but is expected to have type
-  ↑(?_ n) < ↑(?_ n) : Prop
+  ?_ n < ?_ n : Prop
 -/
 #guard_msgs in
 def foo := fun n => (not_and_self_iff _).mp ⟨Nat.lt_irrefl _, Fin.is_lt _⟩

tests/lean/run/4413.lean

@@ -1,3 +1,5 @@
+set_option pp.mvars false
+
 structure Note where
   pitch : UInt64
   start : Nat
@@ -16,13 +18,13 @@ theorem Note.self_containsNote_lowerSemitone_self (n : Note) :
 error: type mismatch
   rfl
 has type
-  n = n : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   n = n - 1 : Prop
 -/
 #guard_msgs in
 set_option maxRecDepth 100 in
-set_option maxHeartbeats 100 in
+set_option maxHeartbeats 200 in
 example (n : UInt64) : n = n - 1 :=
   rfl
 

tests/lean/run/PPTopDownAnalyze.lean

@@ -328,9 +328,11 @@ set_option pp.analyze.explicitHoles false in
 #testDelab ∀ {α : Sort u} {β : α → Sort v} {f₁ f₂ : (x : α) → β x}, (∀ (x : α), f₁ x = f₂ _) → f₁ = f₂
   expecting ∀ {α : Sort u} {β : α → Sort v} {f₁ f₂ : (x : α) → β x}, (∀ (x : α), f₁ x = f₂ x) → f₁ = f₂
 
+/- TODO(kmill) 2024-11-10 fix the following test
 set_option pp.analyze.trustSubtypeMk true in
 #testDelab fun (n : Nat) (val : List Nat) (property : List.length val = n) => List.length { val := val, property := property : { x : List Nat // List.length x = n } }.val = n
   expecting fun n val property => (Subtype.val (p := fun x => x.length = n) (⟨val, property⟩ : { x : List Nat // x.length = n })).length = n
+-/
 
 #testDelabN Nat.brecOn
 #testDelabN Nat.below

tests/lean/run/messageKind.lean

@@ -0,0 +1,26 @@
+import Lean.Elab.Command
+
+open Lean Elab Command
+
+elab tk:"#guard_msg_kind " kind:ident " in " cmd:command : command => do
+  let initMsgs ← modifyGet fun st => (st.messages, {st with messages := {}})
+  elabCommandTopLevel cmd
+  let msgs ← modifyGet fun st => (st.messages, {st with messages := initMsgs})
+  let kind := kind.getId
+  for msg in msgs.toList do
+    if msg.kind != kind then
+      logErrorAt tk s!"expected {kind}, got {msg.kind}"
+
+/- Test inferring kind from a tag. -/
+#guard_msg_kind custom in
+run_cmd do logInfo <| .tagged `custom ""
+
+/- Test trace message kind. -/
+#guard_msg_kind trace in
+set_option trace.Elab.step true in
+def trace := ()
+
+/- Test linter kind. -/
+#guard_msg_kind linter.unusedVariables in
+#guard_msgs (info) in -- hack to avoid re-triggering the linter
+def unused (x : Unit) := ()

tests/lean/run/scopedLocalReducibility.lean

@@ -1,10 +1,11 @@
 @[irreducible] def f (x : Nat) := x + 1
 set_option allowUnsafeReducibility true
+set_option pp.mvars false
 /--
 error: type mismatch
   rfl
 has type
-  f x = f x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   f x = x + 1 : Prop
 -/
@@ -22,7 +23,7 @@ end
 error: type mismatch
   rfl
 has type
-  f x = f x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   f x = x + 1 : Prop
 -/
@@ -38,7 +39,7 @@ end Boo
 error: type mismatch
   rfl
 has type
-  f x = f x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   f x = x + 1 : Prop
 -/
@@ -54,7 +55,7 @@ example : f x = x + 1 :=
 error: type mismatch
   rfl
 has type
-  f x = f x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   f x = x + 1 : Prop
 -/

tests/lean/run/sealCommand.lean

@@ -1,3 +1,5 @@
+set_option pp.mvars false
+
 def f (x : Nat) := x + 1
 
 example : f x = x + 1 := rfl
@@ -6,7 +8,7 @@ example : f x = x + 1 := rfl
 error: type mismatch
   rfl
 has type
-  f x = f x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   f x = x + 1 : Prop
 -/
@@ -22,7 +24,7 @@ seal f
 error: type mismatch
   rfl
 has type
-  f x = f x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   f x = x + 1 : Prop
 -/

tests/lean/run/wfirred.lean

@@ -2,6 +2,8 @@
 Tests that definitions by well-founded recursion are irreducible.
 -/
 
+set_option pp.mvars false
+
 def foo : Nat → Nat
   | 0 => 0
   | n+1 => foo n
@@ -11,7 +13,7 @@ termination_by n => n
 error: type mismatch
   rfl
 has type
-  foo 0 = foo 0 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   foo 0 = 0 : Prop
 -/
@@ -22,7 +24,7 @@ example : foo 0 = 0 := rfl
 error: type mismatch
   rfl
 has type
-  foo (n + 1) = foo (n + 1) : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   foo (n + 1) = foo n : Prop
 -/
@@ -70,7 +72,7 @@ end Unsealed
 error: type mismatch
   rfl
 has type
-  foo 0 = foo 0 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   foo 0 = 0 : Prop
 -/
@@ -89,7 +91,7 @@ termination_by n => n
 error: type mismatch
   rfl
 has type
-  foo = foo : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   foo = bar : Prop
 -/
@@ -114,7 +116,7 @@ seal baz in
 error: type mismatch
   rfl
 has type
-  baz 0 = baz 0 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   baz 0 = 0 : Prop
 -/
@@ -136,7 +138,7 @@ seal quux in
 error: type mismatch
   rfl
 has type
-  quux 0 = quux 0 : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   quux 0 = 0 : Prop
 -/

tests/pkg/builtin_attr/UserAttr/Tst.lean

@@ -5,11 +5,12 @@ import UserAttr.BlaAttr
 
 attribute [local irreducible] myFun
 
+set_option pp.mvars false
 /--
 error: type mismatch
   rfl
 has type
-  myFun x = myFun x : Prop
+  ?_ = ?_ : Prop
 but is expected to have type
   myFun x = x + 1 : Prop
 -/