Fix transmutability type mismatch bug by lsunsi · Pull Request #163946 · rust-lang/rust

lsunsi · 2026-10-07T14:46:53Z

The change was done as instructed by @ShoyuVanilla and @lcnr on Zulip.
There are some leftover questions I'll add as comments (self review).
But the original examples are both fixed.

rustbot · 2026-10-07T14:46:59Z

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

rustbot · 2026-10-07T14:47:02Z

ShoyuVanilla is currently at their maximum review capacity.
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lcnr · 2026-10-12T10:57:22Z

+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ [next] compile-flags: -Znext-solver
+//@ check-fail


what's that for?

View changes since the review

what 'that' exactly?
if you're referring to the revisions and check fail added to this test, I think I just added it to all transmute. does it not make sense in this one? is it because it's a rustfix test?

I missed this test this while reviewing 😅 I think it would be great if we have why we need this test and what this test is for. (Not just for this one but all the new ones we add) If we already have a related issue or discussion that explains it well, just adding a link to it would be enough

Yes, definitely! But since I'm not adding the test itself (the file was already there), I can't tell exactly what it is for. I'll look into the original commit and try to figure out.

Also I'll add links or comments to the other ones

The new tests are these four:

tests/ui/transmutability/pointer-aligned-to-next-solver.rs ((came from https://hackmd.io/ydc_nIbHQqG-ctMDapXYTg#featuretransmutability, which is already a doc test)

tests/ui/transmutability/transmute-from-next-solver.rs (came from https://hackmd.io/ydc_nIbHQqG-ctMDapXYTg#featuretransmutability, which is already a doc test, but it's pretty close to -Znext-solver=globally breaks TransmuteFrom<&T> #161251)

tests/ui/transmutability/vec-recycle-next-solver.rs (came from zulip which is also a doc test mentioned by @lcnr )

tests/ui/transmutability/with-condition-nested-goals.rs (this one has a comment explaining why it's there)

So considering 3 of the 4 tests are doc tests already, do you think it's best to remove them?
The third one is the one we discussed before, about testing the "add_goals", so I think it's worth keeping (and it's already commented explaining this).

I originally asked about "//@ check-fail", that is unnecessary I think

I would not add the two doc tests

Oh, because check-fail is the default right?
I thought explicit would be better, but I'll remove since it's implied.

@ShoyuVanilla what do you think, keep or drop tests/ui/transmutability/pointer-aligned-to-next-solver.rs and tests/ui/transmutability/transmute-from-next-solver.rs?

Yeah dropping doc tests sgmt

@lcnr @ShoyuVanilla removed both and removed the directive 13694b6

thanks for the feedbacks (:

lcnr · 2026-10-12T12:07:26Z

@bors delegate+

rust-bors · 2026-10-12T12:07:29Z

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

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

View changes since this delegation.

ShoyuVanilla · 2026-10-12T13:52:23Z

@bors r=lcnr,ShoyuVanilla rollup

rust-bors · 2026-10-12T13:52:27Z

📌 Commit 13694b6 has been approved by lcnr,ShoyuVanilla

It is now in the queue for this repository.

@ShoyuVanilla

…uVanilla Fix transmutability type mismatch bug Fixes rust-lang#161251 r? @ShoyuVanilla The change was done as instructed by @ShoyuVanilla and @lcnr on Zulip. There are some leftover questions I'll add as comments (self review). But the original examples are both fixed.

@ShoyuVanilla

…uVanilla Fix transmutability type mismatch bug Fixes rust-lang#161251 r? @ShoyuVanilla The change was done as instructed by @ShoyuVanilla and @lcnr on Zulip. There are some leftover questions I'll add as comments (self review). But the original examples are both fixed.

…uwer Rollup of 8 pull requests Successful merges: - #164196 (`rust-analyzer` subtree update) - #164037 (Restrict application of optimization attributes from instance) - #164201 (Improve `--bless` output for `tests/debuginfo`) - #164202 ([rustdoc] Move the creation of `IndividualTestOptions` into the test runner closure to ensure the temporary folder is removed right after the test is done running) - #162140 (fn_addr_eq: we actually can guarantee basically nothing) - #163946 (Fix transmutability type mismatch bug) - #163978 (Copy over some methods from At to InferCtxt) - #164045 (-Zassumptions-on-binders: replace region vars with bound vars when handling alias outlives')

@ShoyuVanilla

Rollup merge of #163946 - lsunsi:next-transmute, r=lcnr,ShoyuVanilla Fix transmutability type mismatch bug Fixes #161251 r? @ShoyuVanilla The change was done as instructed by @ShoyuVanilla and @lcnr on Zulip. There are some leftover questions I'll add as comments (self review). But the original examples are both fixed.

lcnr · 2026-10-12T21:49:07Z

@lsunsi does this fix the issues added in #163946?

lsunsi · 2026-10-12T21:55:38Z

@lcnr do you mean #161251? If so, yes, it fixes it.

lcnr · 2026-10-13T07:40:43Z

yikes xd, I meant #149228 😅

lsunsi · 2026-10-13T10:12:19Z

@lcnr ./x test tests/ui/transmutability/transmutability-coherence.rs --compare-mode next-solver

The test added in #149228 passes cleanly on compare mode.
I'm not sure why the current PR is equivalent to the referred change, but it seems to be.

Do you want me to open a PR with just the new test? Or maybe just close the PR directly?

lcnr · 2026-10-13T10:27:15Z

please add these tests in a separate PR, yeah 😊

lsunsi · 2026-10-13T10:54:33Z

@lcnr here we go #164257 (:

EDIT: forgot to assign you as reviewer. should be a trivial approve, should I re-assign you?

Add transmutability test to cover for superseded PR Adds a test present in rust-lang#149228 that was fixed by rust-lang#163946.

Rollup merge of #164257 - lsunsi:pull149228, r=ShoyuVanilla Add transmutability test to cover for superseded PR Adds a test present in #149228 that was fixed by #163946.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Oct 7, 2026

rustbot assigned ShoyuVanilla Oct 7, 2026

lsunsi commented Oct 7, 2026

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lcnr reviewed Oct 7, 2026

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lsunsi force-pushed the next-transmute branch from 07cad77 to 3148361 Compare October 9, 2026 20:25

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lsunsi force-pushed the next-transmute branch from 2efe77b to 73189a9 Compare October 10, 2026 13:32

lsunsi added 4 commits October 10, 2026 10:37

Uplift flatten_answer_tree to next-solver

c1c3daa

Add test for transmute recycle on next solver

61d4201

Update is_transmutable on next solver to consider nested goals

01d70ab

Update test to reflect previous fix

247b4de

lcnr reviewed Oct 12, 2026

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Drop two repeated tests and an unecessary directive

13694b6

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 Oct 12, 2026

JonathanBrouwer mentioned this pull request Oct 12, 2026

Rollup of 9 pull requests #164211

Closed

This was referenced Oct 12, 2026

Rollup of 9 pull requests #164212

Closed

Rollup of 8 pull requests #164216

Merged

rust-bors Bot merged commit cee2a0d into rust-lang:main Oct 12, 2026
14 checks passed

rustbot added this to the 1.101.0 milestone Oct 12, 2026

lsunsi deleted the next-transmute branch October 12, 2026 20:07

funsafemath mentioned this pull request Oct 13, 2026

Assume::NOTHING doesn't check lifetimes #164246

Open

lcnr mentioned this pull request Oct 13, 2026

transmutability: Stall new solver when inference variables remain #149228

Closed

lsunsi mentioned this pull request Oct 13, 2026

Add transmutability test to cover for superseded PR #164257

Merged

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