Reject linked dylib EII default overrides by qaijuang · Pull Request #156370 · rust-lang/rust

qaijuang · 2026-05-09T17:58:50Z

This PR rejects explicit EII implementations that would override a default implementation already selected through a linked dylib.

The check is intentionally split:

rustc_passes keeps the early, format-independent checks for missing impls and duplicate explicit impls.
rustc_codegen_ssa checks the default-vs-explicit conflict during linking, using the dependency formats selected for the final artifact.

Fixes #156320.

rustbot · 2026-05-09T20:28:21Z

r? @mejrs

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qaijuang · 2026-05-09T20:28:42Z

cc @bjorn3

mejrs · 2026-05-09T21:51:59Z

r? @jdonszelmann (or @bjorn3 perhaps)

rustbot · 2026-05-09T21:52:04Z

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bjorn3 · 2026-05-10T17:08:25Z

Thinking about this a bit more, I'm wondering if maybe check_externally_implementable_items should be done only at link time? tcx.used_crate_source() may report that only a dylib exists even when at link time an rlib will be available and linked in. And tcx.dependency_formats() will report everything as NotLinked inside rlibs and would ideally only be called during the link step for -Zno-link/-Zlink-only to work (it is currently broken because dependency_formats is called during codegen. i've been working on moving this call to the link step for the past several months). On the other hand for all cases that the check caught before this PR, doing it before linking is fine. So splitting it into separate checks for duplicate explicit impls and for a default impl conflicting with an explicit impl would preserve early error messages (especially for cargo check) What do you think @jdonszelmann?

qaijuang · 2026-05-11T10:16:56Z

Thinking about this a bit more, I'm wondering if maybe check_externally_implementable_items should be done only at link time? tcx.used_crate_source() may report that only a dylib exists even when at link time an rlib will be available and linked in. And tcx.dependency_formats() will report everything as NotLinked inside rlibs and would ideally only be called during the link step for -Zno-link/-Zlink-only to work (it is currently broken because dependency_formats is called during codegen.

Nice catch @bjorn3

So splitting it into separate checks for duplicate explicit impls and for a default impl conflicting with an explicit impl would preserve early error messages (especially for cargo check)

right? seems like the next best move

qaijuang · 2026-05-11T15:23:13Z

@bjorn3 I'm done with the split, what do you think?

jdonszelmann · 2026-05-28T12:34:59Z

@bjorn3 that approach seems reasonable to me

rustbot · 2026-07-08T09:20:30Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

qaijuang · 2026-07-08T11:31:07Z

@rustbot ready

bjorn3

r=me with the below changes.

View changes since this review

bjorn3 · 2026-07-08T15:40:53Z

Thanks!

@bors r+

rust-bors · 2026-07-08T15:40:57Z

📌 Commit 41bdaed has been approved by bjorn3

It is now in the queue for this repository.

…e, r=bjorn3 Reject linked dylib EII default overrides This PR rejects explicit EII implementations that would override a default implementation already selected through a linked dylib. The check is intentionally split: - rustc_passes keeps the early, format-independent checks for missing impls and duplicate explicit impls. - rustc_codegen_ssa checks the default-vs-explicit conflict during linking, using the dependency formats selected for the final artifact. Fixes rust-lang#156320.

…uwer Rollup of 25 pull requests Successful merges: - #158871 (add relnotes for 1.97.0) - #158968 (stdarch subtree update) - #154445 (rustdoc: Represent `--output-format=json` coverage and ir differently) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158495 (Rename HAS_CT_PROJECTION to HAS_CONST_ALIAS) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158655 (Fix coroutine MIR saved local remapping) - #158666 (Carry the `b_offset` inside `BackendRepr::ScalarPair`) - #158912 (Introduce new bootstrap config section for PGO configuration) - #158920 (Update wasm-component-ld to 0.5.26) - #158926 (wrapping_sh* methods: clarify underspecified reference) - #158927 (add core test run with `-Zforce-intrinsic-fallback`) - #158932 (Do not build the compiler when invoking `x perf compare`) - #158937 (Emit the emscripten entry point as `__main_argc_argv`) - #151379 (Stabilize `VecDeque::retain_back` from `truncate_front`) - #156548 ( Library support for aarch64-unknown-linux-pauthtest target) - #158307 (CI job for parallel frontend ui tests) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158741 (Simplify `Option::into_flat_iter` signature) - #158807 (Add regression test for CString::clone_into unwind safety) - #158862 (Fix the span for parameter suggestion ) - #158883 (tests: fix enum-match.rs to handle LLVM 23)

…e, r=bjorn3 Reject linked dylib EII default overrides This PR rejects explicit EII implementations that would override a default implementation already selected through a linked dylib. The check is intentionally split: - rustc_passes keeps the early, format-independent checks for missing impls and duplicate explicit impls. - rustc_codegen_ssa checks the default-vs-explicit conflict during linking, using the dependency formats selected for the final artifact. Fixes rust-lang#156320.

Rollup of 25 pull requests Successful merges: - #158871 (add relnotes for 1.97.0) - #158968 (stdarch subtree update) - #157690 (codegen_ssa: pack small const aggregates into immediate stores) - #158541 (Move `std::io::Write` to `core::io`) - #154445 (rustdoc: Represent `--output-format=json` coverage and ir differently) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158495 (Rename HAS_CT_PROJECTION to HAS_CONST_ALIAS) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158655 (Fix coroutine MIR saved local remapping) - #158666 (Carry the `b_offset` inside `BackendRepr::ScalarPair`) - #158870 (std: merge the unix-like io::error modules into one file) - #158920 (Update wasm-component-ld to 0.5.26) - #158926 (wrapping_sh* methods: clarify underspecified reference) - #158927 (add core test run with `-Zforce-intrinsic-fallback`) - #158932 (Do not build the compiler when invoking `x perf compare`) - #158937 (Emit the emscripten entry point as `__main_argc_argv`) - #151379 (Stabilize `VecDeque::retain_back` from `truncate_front`) - #156144 (Better docs for PartialEq (includes macro rename)) - #156548 ( Library support for aarch64-unknown-linux-pauthtest target) - #158307 (CI job for parallel frontend ui tests) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158741 (Simplify `Option::into_flat_iter` signature)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 9, 2026

qaijuang marked this pull request as ready for review May 9, 2026 20:28

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 9, 2026

rustbot assigned mejrs May 9, 2026

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rustbot assigned jdonszelmann and unassigned mejrs May 9, 2026

qaijuang force-pushed the eii-dylib-default-override branch from dfc410a to 44e8bb8 Compare May 11, 2026 15:11

qaijuang changed the title ~~Reject EII overrides of dylib defaults~~ Reject linked dylib EII default overrides May 11, 2026

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rustbot added has-merge-commits PR has merge commits, merge with caution. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 14, 2026

qaijuang force-pushed the eii-dylib-default-override branch from 5af5be7 to b41cef3 Compare May 14, 2026 20:14

rustbot removed has-merge-commits PR has merge commits, merge with caution. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 14, 2026

bjorn3 reviewed May 28, 2026

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qaijuang force-pushed the eii-dylib-default-override branch from 3827ccb to 621745e Compare May 28, 2026 17:36

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 8, 2026

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address suggestions

3378897

qaijuang force-pushed the eii-dylib-default-override branch from 48d4bf3 to 3378897 Compare July 8, 2026 12:20

bjorn3 approved these changes Jul 8, 2026

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bjorn3 assigned bjorn3 and unassigned jdonszelmann Jul 8, 2026

bjorn3 added the F-extern_item_impls `#![feature(extern_item_impls)]` label Jul 8, 2026

address follow up nits

41bdaed

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 8, 2026

JonathanBrouwer mentioned this pull request Jul 8, 2026

Rollup of 12 pull requests #158963

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JonathanBrouwer mentioned this pull request Jul 8, 2026

Rollup of 14 pull requests #158971

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JonathanBrouwer mentioned this pull request Jul 8, 2026

Rollup of 25 pull requests #158973

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Rollup of 25 pull requests #158977

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jhpratt mentioned this pull request Jul 8, 2026

Rollup of 25 pull requests #158986

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