Incorrect unused variable warning in lambda with pattern match and type signature

Prerequisites

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• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

Incorrect "unused variable" warnings are reported around lambdas with pattern matches and explicit type annotations. See example below.

Context

Steps to Reproduce

#check λα (p : α → Prop) (⟨x, _⟩ : {a // p a}) => x
--         ^                             ^ ^
--         1                             2 3

Expected behavior: No unused variable warnings.

Actual behavior: Lean reports 3 unused variable warnings at the indicated locations:

• Lean claims p at location 1 is unused, even though though 2 is its use.
• Lean claims p at location 2 and a at location 3 are unused, even though these are not the variables' binding sites.

Versions

4.13.0

Additional Information

The "2" warning goes away if we use p in the body of the lambda:

#check λα (p : α → Prop) (⟨x, _⟩ : {a // p a}) => (x, p)
--         ^                             ^ ^
--         1                             2 3

as if Lean believes 2 is p's binding site which in turn shadows the p bound at 1.

The problem goes away if matching is moved out of the lambda:

#check λα (p : α → Prop) (x : {a // p a}) => match x with | ⟨x, _⟩ => x

The use of (Subtype.mk _ _) versus ⟨_, _⟩ makes no difference.

Impact

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Start by running the minimal lambda and pattern-match reproduction against Lean 4.13.0 and the latest nightly, then compare it with the two alternatives in the issue. Done means the original example produces no incorrect unused-variable warnings while the reported behavior remains covered by a regression test.