`simp` uses `congr` lemmas that are not visible

[datokrat]

Prerequisites

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• [x] Check that your issue is not already filed: https://github.com/leanprover/lean4/issues
• [x] Reduce the issue to a minimal, self-contained, reproducible test case. Avoid dependencies to Mathlib or Batteries.
• [x] 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

Private lemmas marked as @[congr] from imported modules are used by simp even though they are not visible, causing unknown constant errors.

Steps to Reproduce

1. Check out the Lake project in this branch: https://github.com/datokrat/lean-bug-reproductions/tree/bugs7
2. Open Reproductions/Basic.lean and observe the error.

Reproductions/Dependency.lean:

module

public def f : Nat → Nat := sorry

@[congr]
theorem t (h : m = n) : f m = f n := sorry

Reproductions/Basic.lean:

module

import Reproductions.Dependency

/-- error: Unknown constant `_private.Reproductions.Dependency.0.t` -/
#guard_msgs in
theorem u (h : m = n) : f m = f n := by
  simp [h]

Expected behavior:

simp should only use congr lemmas that are visible. (In the given example, theorem u should succeed because simp actually doesn't need to use a specialized congr lemma.)

Actual behavior:

An unknown constant error is caused by simp.

Versions

Lean 4.27.0-nightly-2025-11-30
Target: arm64-apple-darwin24.6.0 macOS

Impact

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[nomeata]

Probably a missing exportEntry function that prevents these entries from entering the public environment in the first place, somewhere near

https://github.com/leanprover/lean4/blob/057b70b443d99c08be8b0f193cfa0690b42d0185/src/Lean/Meta/Tactic/Simp/SimpCongrTheorems.lean#L49

or - if possible - in SimpleScopedEnvExtension directly in

https://github.com/leanprover/lean4/blob/057b70b443d99c08be8b0f193cfa0690b42d0185/src/Lean/ScopedEnvExtension.lean#L246

so that all users benefit