Regression 1.96.1 → 1.97.0: "missing optimized MIR" for pub fn glob-reexported alongside a restricted glob duplicate

Building a crate that calls dep::f() fails with error: missing optimized MIR for `f` in the crate `dep` when f — an ordinary non-generic pub fn — is exported from dep only through a public glob re-export and a second, private glob also imports it into the same module with restricted visibility. 1.96.1 compiles this fine; 1.97.0 fails. Found while building a private ~16-crate workspace.

Reproduction

// dep/src/lib.rs
mod inner {
    pub fn f() -> u32 { 42 }
}
mod facade {
    pub(crate) use super::inner::f;
}
#[allow(unused_imports)]
use facade::*;
pub use inner::*;

// app/src/lib.rs  (app depends on dep by path)
pub fn call_f() -> u32 { dep::f() }

$ cargo +1.96.1 build --release
warning: unused import: `super::inner::f`
    Finished `release` profile [optimized] target(s) in 0.25s

$ cargo +1.97.0 build --release
warning: unused import: `super::inner::f`
warning: function `f` is never used
error: missing optimized MIR for `f` in the crate `dep`
  |
note: missing optimized MIR for this item (was the crate `dep` compiled with `--emit=metadata`?)
error: could not compile `app` (lib) due to 1 previous error

Also fails in default cargo build (see details), on 1.98.0-beta.1, and on 1.99.0-nightly (2026-07-08). Nightly only: RUSTFLAGS=-Zalways-encode-mir masks it.

Mechanism

Two queries disagree about f. Name resolution still exports it at pub — dep::f resolves fine downstream and f stays cross_crate_inlinable — but the effective-visibility computation walks only the first-arrived glob declaration's reexport chain (here the restricted facade route), capping f at pub(crate). Everything driven by effective visibilities then treats f as not exported: the new spurious function `f` is never used warning above is the tell, f drops out of reachable_set, and should_encode_mir skips encoding its optimized MIR while downstream crates still try to inline it — hence the collector error.

Bisection

With cargo bisect-rustc v0.6.11 (plain cargo build of the repro, --regress error):

searched nightlies: from nightly-2026-04-05 to nightly-2026-05-10
regressed nightly: nightly-2026-05-01
regressed commit: https://github.com/rust-lang/rust/commit/a021a7796f66600f46013d6c8d1dfc9e8d7f4a92 (rollup #155979)

Likely PR: #154149 (resolve: Extend ambiguous_import_visibilities deprecation lint to glob-vs-glob ambiguities) — the only shape-matching PR in the rollup; corroboration in the details below.

We have a validated fix: fix PR: #159039.

Version

rustc 1.97.0 (2d8144b78 2026-07-07)
binary: rustc
commit-hash: 2d8144b7880597b6e6d3dfd63a9a9efae3f533d3
commit-date: 2026-07-07
host: aarch64-apple-darwin
release: 1.97.0
LLVM version: 22.1.6

@rustbot label +regression-from-stable-to-stable +A-resolve +A-visibility +T-compiler +C-bug +S-has-bisection

Start with the two-crate reproduction in dep/src/lib.rs and app/src/lib.rs, confirming the failure on 1.97.0 and the bisected commit a021a7796f66600f46013d6c8d1dfc9e8d7f4a92. Read the visibility changes associated with PR #154149 and compare the validated fix in PR #159039. Done means the reproduction builds successfully without the missing optimized MIR error and the regression is covered.