Rip out old solver coherence by sjwang05 · Pull Request #161491 · rust-lang/rust

sjwang05 · 2026-08-22T00:28:45Z

cc #t-types/call-for-participation > rip out old solver coherence support

Probably best reviewed commit-by-commit with ignore-whitespace.

#160668 replaced the last remaining place where old solver was still used by default in coherence with new solver. This PR removes code that was only used during coherence by the old solver, so now new-solver coherence is the only way to do coherence. So we don't confuse users, passing -Znext-solver=coherence and =no now do the exact same thing.

We also remove tracking intercrate ambiguity causes, since afaict the new solver uses a completely different path.

Everything else is either removing code that is now unreachable, or removing a condition that is now always true.

r? lcnr

rustbot · 2026-08-22T00:28:48Z

Some changes occurred in src/tools/compiletest

cc @jieyouxu

rustc-dev-guide is developed in its own repository. If possible, consider making this change to rust-lang/rustc-dev-guide instead.

cc @BoxyUwU, @tshepang

sjwang05 · 2026-08-22T00:30:20Z

-    selcx: &mut SelectionContext<'cx, 'tcx>,
+#[instrument(level = "debug", skip(infcx), ret)]
+fn impl_intersection_has_impossible_obligation<'a, 'tcx>(
+    infcx: &InferCtxt<'tcx>,


The selcx was only ever used with the old solver, hence we just pass the infcx directly now.

View changes since the review

rustbot · 2026-08-22T05:35:02Z

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

miri is developed in its own repository. If the Miri part of this change can be broken out, consider making this change to rust-lang/miri instead. However, if Miri needs adjusting for rustc changes, just ignore this message.

cc @rust-lang/miri

Rip out old solver coherence cc [#t-types/call-for-participation > rip out old solver coherence support](https://rust-lang.zulipchat.com/#narrow/channel/618216-t-types.2Fcall-for-participation/topic/rip.20out.20old.20solver.20coherence.20support/with/613938355) Probably best reviewed commit-by-commit with ignore-whitespace. rust-lang#160668 replaced the last remaining place where old solver was still used by default in coherence with new solver. This PR removes code that was only used during coherence by the old solver, so now new-solver coherence is the *only* way to do coherence. So we don't confuse users, passing `-Znext-solver=coherence` and `=no` now do the exact same thing. We also remove tracking intercrate ambiguity causes, since afaict the new solver uses a completely different path. Everything else is either removing code that is now unreachable, or removing a condition that is now always true. r? lcnr

…uwer Rollup of 8 pull requests Successful merges: - #163645 (add `ignore-compare-mode-next-solver` to all next-solver tests) - #163663 (reflection: fix ICE when TypeId::info called on ADT) - #163454 (Improve suggestion for lifetime preceding type in generics) - #163561 (tests: accept noundef in a couple more places) - #163633 (core: io: clean `unused_variables` lint under `no_io_statics`) - #163681 (Make the tracking issue template better suited for experiments) - #163685 (Avoid long iterator chain in all_rust_features) - #163690 (refactor: migrate to LLVM-C's `LLVMGetOrInsertFunction`) Failed merges: - #161491 (Rip out old solver coherence)

khyperia · 2026-10-03T16:02:22Z

omg im so sorry, incredibly unfortunate merge conflicts. I've never used delegate+ before but hopefully it works for this? r=me when you've resolved the merge conflicts

@bors delegate+

rust-bors · 2026-10-03T16:02:25Z

✌️ @sjwang05, you can now approve this pull request!

If @khyperia told you to "r=me" after making some further change, then please make that change and post @bors r=khyperia.

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sjwang05 · 2026-10-03T20:56:12Z

@bors r=khyperia

rust-bors · 2026-10-03T20:56:15Z

📌 Commit 46d0705 has been approved by khyperia

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #158102 (When compiling without a specified `--edition`, emit a message) - #162027 (std: add `fs::rename_noreplace`) - #162761 (Lower attributes for functions without bodies) - #163161 (implement FCW for `rustc_allowed_through_unstable_modules` items) - #163613 (Tweak the rendering of "not general enough" errors on the old trait solver) - #162062 (core: fix the docs of PanicInfo::location) - #163140 (document safety requirements for atomic intrinsics) - #163342 (Don't imply incorrect things about `Global` in the docs of `System`) - #163445 (Add safety comments for alloc::str) - #163503 (Mark Rc strong/weak count methods must_use) - #163548 (fs::set_permissions_nofollow: Android support, test cleanup) - #163585 ([triagebot] Create `debugger_visualizer` assign group) - #163597 (Add `SplitPathsRef` implementation for motor to make std build) - #163602 (Move media & home dirs tests to fs tests.) - #163667 (Finalize changes on expect messages for library/core/src/fmt/mod.rs) - #163682 ([rustdoc] Correctly link to (imported) enum variants with "jump to def") - #163683 (Fix GCC codegen backend comment in bootstrap) - #163703 (Move more `rustdoc-html tests` in the right location) Failed merges: - #161491 (Rip out old solver coherence)

Rollup of 18 pull requests Successful merges: - #158102 (When compiling without a specified `--edition`, emit a message) - #162761 (Lower attributes for functions without bodies) - #163161 (implement FCW for `rustc_allowed_through_unstable_modules` items) - #163613 (Tweak the rendering of "not general enough" errors on the old trait solver) - #162062 (core: fix the docs of PanicInfo::location) - #163140 (document safety requirements for atomic intrinsics) - #163342 (Don't imply incorrect things about `Global` in the docs of `System`) - #163445 (Add safety comments for alloc::str) - #163503 (Mark Rc strong/weak count methods must_use) - #163548 (fs::set_permissions_nofollow: Android support, test cleanup) - #163585 ([triagebot] Create `debugger_visualizer` assign group) - #163597 (Add `SplitPathsRef` implementation for motor to make std build) - #163602 (Move media & home dirs tests to fs tests.) - #163667 (Finalize changes on expect messages for library/core/src/fmt/mod.rs) - #163682 ([rustdoc] Correctly link to (imported) enum variants with "jump to def") - #163683 (Fix GCC codegen backend comment in bootstrap) - #163703 (Move more `rustdoc-html tests` in the right location) - #163725 (some crashes fixed with next-solver) Failed merges: - #161491 (Rip out old solver coherence)

rustbot · 2026-10-04T11:25:07Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

sjwang05 · 2026-10-04T11:25:41Z

@bors r=khyperia

this time, surely.

rust-bors · 2026-10-04T11:25:44Z

📌 Commit 3a7efa2 has been tentatively approved by khyperia

It will be put into the queue for this repository once PR CI succeeds.

rustbot assigned lcnr Aug 22, 2026

sjwang05 commented Aug 22, 2026

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lcnr reviewed Sep 8, 2026

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This was referenced Oct 3, 2026

Rollup of 7 pull requests #163691

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Rollup of 8 pull requests #163695

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sjwang05 force-pushed the no-old-coherence branch from d850b33 to 46d0705 Compare October 3, 2026 19:29

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jhpratt mentioned this pull request Oct 3, 2026

Rollup of 18 pull requests #163729

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Rollup of 18 pull requests #163735

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sjwang05 added 2 commits October 4, 2026 04:19

yeet old solver coherence

add63e4

bless tests

3a7efa2

sjwang05 force-pushed the no-old-coherence branch from 46d0705 to 3a7efa2 Compare October 4, 2026 11:25

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