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fix: simp argument elaboration metacontext depth #10615

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fix: simp argument elaboration metacontext depth #10615

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b92da23
fix: simp argument elaboration metacontext depth
kmill Sep 29, 2025
b42008f
fix
kmill Sep 29, 2025
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2 changes: 1 addition & 1 deletion src/Lean/Elab/Tactic/Simp.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,7 @@ private def elabDeclToUnfoldOrTheorem (config : Meta.ConfigWithKey) (id : Origin

private def elabSimpTheorem (config : Meta.ConfigWithKey) (id : Origin) (stx : Syntax)
(post : Bool) (inv : Bool) : TermElabM ElabSimpArgResult := do
let thm? ← Term.withoutModifyingElabMetaStateWithInfo <| withRef stx do
let thm? ← withNewMCtxDepth <| Term.withoutModifyingElabMetaStateWithInfo <| withRef stx do
let e ← Term.elabTerm stx .none
Term.synthesizeSyntheticMVars (postpone := .no) (ignoreStuckTC := true)
let e ← instantiateMVars e
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26 changes: 26 additions & 0 deletions tests/lean/run/9286.lean
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@@ -0,0 +1,26 @@
/-!
# Test for issue 9286
https://github.com/leanprover/lean4/issues/9286

Previously `simp` would create a type incorrect term.
The proximal issue was that the universe level metavariable in the type `a` was being
abstracted without abstracting `a` itself.
However, we should not be abstracting `a`; instead, simp arguments should be elaborated
with a new metacontext depth -- this is in part justified by the fact that elaboration
of simp arguments should not be assigning metavariables.
-/

inductive SomeThing.{u} : Prop where
| mk (_ : PUnit.{u})

/-!
Previously `simp` would succeed and lead to a kernel typechecking error.
Now, `simp` correctly makes no progress.
-/
/-- error: `simp` made no progress -/
#guard_msgs in
set_option pp.universes true in
def testMe (a : PUnit) : PLift SomeThing := by
constructor
have := SomeThing.mk a
simp only [SomeThing.mk a]
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