simp fails to see through abbrev

[JLimperg]

Prerequisites

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Description

The following simp call fails to unfold the abbrev Bar.

axiom Foo : Prop → Prop

abbrev Bar := ∀ P, True → Foo P

example (P : Prop) (h : Bar) : False := by
  simp only [forall_const] at h -- fails

example (P : Prop) (h : Bar) : False := by
  unfold Bar at h
  simp only [forall_const] at h -- succeeds

Expected behavior: both simp calls succeed.

Actual behavior: the first simp call fails.

Additional Information

The issue does not occur with Foo : Prop and Bar := True -> Foo.

Versions

"4.12.0-nightly-2024-10-02"

Impact

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[leodemoura]

This is not a bug. In the first example, forall_const is not applicable because we cannot unify ?a -> ?b with Bar. Note that Bar is unfolded during unification, but ?a -> ?b and ∀ P, True → Foo P cannot be unified.
In the second example, forall_const is applied to the subterm True -> Foo P.