fix: run enableRealizationsForConst on sizeOf decls

This runs enableRealizationsForConst on sizeOf declarations. Fixes #10573.

src/Lean/Meta/SizeOf.lean

@@ -161,6 +161,7 @@ partial def mkSizeOfFn (recName : Name) (declName : Name): MetaM Unit := do
               safety      := DefinitionSafety.safe
               hints       := ReducibilityHints.abbrev
             }
+            enableRealizationsForConst declName
 
 /--
   Create `sizeOf` functions for all inductive datatypes in the mutual inductive declaration containing `typeName`
@@ -518,6 +519,7 @@ def mkSizeOfInstances (typeName : Name) : MetaM Unit := do
                         hints       := .abbrev
                       }
                     addInstance instDeclName AttributeKind.global (eval_prio default)
+                    enableRealizationsForConst instDeclName
           if genSizeOfSpec.get (← getOptions) then
             mkSizeOfSpecTheorems indInfo.all.toArray fns recMap
 

tests/lean/run/issue10573.lean

@@ -0,0 +1,32 @@
+
+inductive Tree (α : Type) where
+  | leaf : α → Tree α
+  | node : Array (Tree α) → Tree α
+
+def Tree.map {α β} (f : α → β) : Tree α → Tree β
+  | .leaf x => .leaf (f x)
+  | .node ts => .node (ts.map (Tree.map f))
+
+def Tree.map' {α β} [SizeOf α]: (t : Tree α) → (f : (x : α) → sizeOf x < sizeOf t → β) → Tree β
+  | .leaf x, f => .leaf (f x (by simp))
+  | .node ts, f => .node (ts.attach.map (fun ⟨t, ht⟩ =>
+    Tree.map' t (fun x hx => f x (by have := Array.sizeOf_lt_of_mem ht; grind [node.sizeOf_spec]))))
+
+/--
+error: Tactic `try?` failed: consider using `grind` manually, or `try? +missing` for partial proofs containing `sorry`
+
+α β : Type
+inst✝ : SizeOf α
+f : α → β
+t : Tree α
+⊢ map f t = t.map' fun x x_1 => f x
+-/
+#guard_msgs in
+theorem Tree.map_eq_map' {α β} [SizeOf α] (f : α → β) (t : Tree α) :
+    Tree.map f t = Tree.map' t (fun x _ => f x) := by try?
+
+
+inductive Tree' where | nil
+
+#guard_msgs in
+example : 0 <= (Tree'.nil : Tree')._sizeOf_1 := by simp [Tree'._sizeOf_1]