Rewrite fails to disambiguate when only one option is valid

[b-mehta]

Prerequisites

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Description

Rewrite fails to disambiguate when only one option is valid

Context

theorem add_succ : true = true := rfl

open Nat

#check add_succ -- Nat.add_succ
#check (add_succ : true = true) -- _root_.add_succ

example (x y : Nat) : x + (y + 1) = (x + y) + 1 := by
  rw [add_succ]
  /-
  ambiguous, possible interpretations
  _root_.add_succ : true = true

  Nat.add_succ : ∀ (n m : Nat), n + succ m = succ (n + m)
  -/

Zulip discussion: https://leanprover.zulipchat.com/#narrow/stream/287929-mathlib4/topic/ambiguous.20rewrite.20when.20only.20one.20is.20valid. The equivalent in Lean 3 succeeds. Thanks to @kmill for minimising. This showed up in porting the exponential-ramsey project.

Steps to Reproduce

Code as above.

Expected behavior: The rewrite succeeds and closes the goal.

Actual behavior: The rewrite fails.

Versions

Lean (version 4.3.0-rc1, commit baa4b68, Release)
MacOS

Additional Information

None

Impact

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