Error on projection of dyn noncompat type in old trait solver - #154992

spirali · 2026-04-08T15:18:39Z

Trying to fix rust-lang/trait-system-refactor-initiative#269

I am not sure that the check is placed into the right place in the code.

r? lcnr

lcnr · 2026-04-09T08:21:11Z

    //~^ ERROR the trait `Foo` is not dyn compatible
    x.method();
-    //~^ ERROR the trait `Foo` is not dyn compatible
+    //~^ ERROR no method named `method` found for reference `&dyn Foo`


View changes since the review

that's annoying :< ideally we'd silence method errors if the self type is not well-formed, tracking that is non-trivial and I don't know how we'd do so myself rn

lcnr · 2026-04-09T08:21:29Z

lgtm, let's do a crater run, there should be exactly 1 regression from this

@bors try

Error on projection of dyn noncompat type in old trait solver

rust-bors · 2026-04-09T10:29:55Z

☀️ Try build successful (CI)
Build commit: a611f2a (a611f2a14e38407ec6717a86a01424ee6fc80762, parent: 1fe72d35998dea48aeecaf7fc07783b0b553f24f)

lcnr · 2026-04-09T11:12:28Z

@craterbot check

craterbot · 2026-04-09T11:12:52Z

👌 Experiment pr-154992 created and queued.
🤖 Automatically detected try build a611f2a
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-04-20T21:36:22Z

🚧 Experiment pr-154992 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-04-22T22:22:36Z

🎉 Experiment pr-154992 is completed!
📊 18 regressed and 6 fixed (886019 total)
📊 5676 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-154992/retry-regressed-list.txt ↩

lcnr · 2026-04-27T08:11:02Z

@craterbot check crates=https://crater-reports.s3.amazonaws.com/pr-154992/retry-regressed-list.txt

craterbot · 2026-04-27T08:11:11Z

👌 Experiment pr-154992-1 created and queued.
🤖 Automatically detected try build a611f2a
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

lcnr · 2026-04-27T08:11:19Z

@craterbot p=1

craterbot · 2026-04-27T08:11:21Z

📝 Configuration of the pr-154992-1 experiment changed.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-04-27T12:04:56Z

🚧 Experiment pr-154992-1 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-04-27T17:19:44Z

🎉 Experiment pr-154992-1 is completed!
📊 13 regressed and 0 fixed (5381 total)
📊 968 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-154992-1/retry-regressed-list.txt ↩

lcnr · 2026-04-29T08:19:48Z

@craterbot check crates=https://crater-reports.s3.amazonaws.com/pr-154992-1/retry-regressed-list.txt p=1

surprising that we have that many spurious regressions still?

it's caused by build OOMs and unlike the new solver, this PR shouldn't really change max-rss in any way 😅 cc @rust-lang/infra

craterbot · 2026-04-29T08:19:54Z

👌 Experiment pr-154992-2 created and queued.
🤖 Automatically detected try build a611f2a
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rust-rfcbot · 2026-08-16T20:33:35Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

lcnr · 2026-08-17T09:27:54Z

+            let tcx = selcx.tcx();
+            if !tcx.is_dyn_compatible(def_id) {
+                let span = obligation.cause.span;
+                let guar = if span.is_dummy()


comment why we can delay bug here

I guess it's that this should be handled in WF instead?

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Comment added

lcnr

final nit, then r=me

View changes since this review

Kobzol · 2026-08-17T09:29:22Z

@bors delegate

rust-bors · 2026-08-17T09:29:25Z

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

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

View changes since this delegation.

spirali · 2026-08-22T07:16:17Z

@bors r=lcnr

rust-bors · 2026-08-22T07:16:19Z

📌 Commit e2fcf35 has been approved by lcnr

It is now in the queue for this repository.

Error on projection of dyn noncompat type in old trait solver Trying to fix rust-lang/trait-system-refactor-initiative#269 I am not sure that the check is placed into the right place in the code. r? lcnr

…uwer Rollup of 19 pull requests Successful merges: - #151061 (Build rustc and codegen backends with -Zembed-metadata=no) - #154992 (Error on projection of dyn noncompat type in old trait solver) - #157949 (Allow self in const generics) - #158588 (trait_selection: fix assumptions-on-binders diagnostics) - #159954 (core: implement float conversion methods) - #160136 (Add `Default` implementation for `std::sync::Once`) - #160835 (resolver diagnostics: don't swallow labels and point out similar items as a note, not a label) - #161048 (Improve the ABI between the panic runtime and libstd) - #161292 (Add safety comments in alloc::Wtf8) - #161444 (Add some `rustc_type_ir` comments) - #161465 (Remove leftover immediate creation) - #159098 (Add Arc/Rc::strong_count_from_raw) - #159282 (Update documentation for `-Zdump-dep-graph`) - #161401 (Remove fields from TypeKind: Bool, Char, Float and Int) - #161431 (bootstrap: (offload) be stricter about selected compiler and paths) - #161451 (Avoid arming the Windows TLS destructor guard in fibers) - #161463 (Add myself to mailmap) - #161476 (Use bitset for locals_with_use_data) - #161483 (Warn about running ui-fulldeps tests in stage 1) Failed merges: - #161443 (add internal DSL for testing binders)

Rollup merge of #154992 - spirali:fix-dyn-projection, r=lcnr Error on projection of dyn noncompat type in old trait solver Trying to fix rust-lang/trait-system-refactor-initiative#269 I am not sure that the check is placed into the right place in the code. r? lcnr

dimpolo · 2026-08-23T02:28:51Z

I noticed some breakage in todays nightly #161536 and my LLM pointed me at this issue

…uwer Rollup of 19 pull requests Successful merges: - rust-lang/rust#151061 (Build rustc and codegen backends with -Zembed-metadata=no) - rust-lang/rust#154992 (Error on projection of dyn noncompat type in old trait solver) - rust-lang/rust#157949 (Allow self in const generics) - rust-lang/rust#158588 (trait_selection: fix assumptions-on-binders diagnostics) - rust-lang/rust#159954 (core: implement float conversion methods) - rust-lang/rust#160136 (Add `Default` implementation for `std::sync::Once`) - rust-lang/rust#160835 (resolver diagnostics: don't swallow labels and point out similar items as a note, not a label) - rust-lang/rust#161048 (Improve the ABI between the panic runtime and libstd) - rust-lang/rust#161292 (Add safety comments in alloc::Wtf8) - rust-lang/rust#161444 (Add some `rustc_type_ir` comments) - rust-lang/rust#161465 (Remove leftover immediate creation) - rust-lang/rust#159098 (Add Arc/Rc::strong_count_from_raw) - rust-lang/rust#159282 (Update documentation for `-Zdump-dep-graph`) - rust-lang/rust#161401 (Remove fields from TypeKind: Bool, Char, Float and Int) - rust-lang/rust#161431 (bootstrap: (offload) be stricter about selected compiler and paths) - rust-lang/rust#161451 (Avoid arming the Windows TLS destructor guard in fibers) - rust-lang/rust#161463 (Add myself to mailmap) - rust-lang/rust#161476 (Use bitset for locals_with_use_data) - rust-lang/rust#161483 (Warn about running ui-fulldeps tests in stage 1) Failed merges: - rust-lang/rust#161443 (add internal DSL for testing binders)

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 8, 2026

rustbot assigned lcnr Apr 8, 2026

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Apr 8, 2026

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rust-bors Bot pushed a commit that referenced this pull request Apr 9, 2026

Auto merge of #154992 - spirali:fix-dyn-projection, r=<try>

a611f2a

Error on projection of dyn noncompat type in old trait solver

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 9, 2026

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Apr 22, 2026

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 27, 2026

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Apr 27, 2026

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 29, 2026

rust-rfcbot removed the final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. label Aug 16, 2026

rust-rfcbot added the to-announce Announce this issue on triage meeting label Aug 16, 2026

rustbot mentioned this pull request Aug 16, 2026

Tracking issue for release notes of #154992: Error on projection of dyn noncompat type in old trait solver #161194

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lcnr reviewed Aug 17, 2026

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e2fcf35

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 Aug 22, 2026

jhpratt mentioned this pull request Aug 22, 2026

Rollup of 19 pull requests #161497

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JonathanBrouwer mentioned this pull request Aug 22, 2026

Rollup of 18 pull requests #161498

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This was referenced Aug 22, 2026

Rollup of 18 pull requests #161501

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Rollup of 19 pull requests #161505

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rust-bors Bot merged commit 9c98028 into rust-lang:main Aug 22, 2026
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rustbot added this to the 1.100.0 milestone Aug 22, 2026

dimpolo mentioned this pull request Aug 23, 2026

cycle detected when checking if trait is dyn-compatible with next-gen trait solver and arbitrary_self_types #161536

Open

This was referenced Aug 27, 2026

stabilize -Znext-solver=coherence again #130654

Merged

Stabilize the next-generation trait solver rust-lang/goals#113

Open

apiraino removed the to-announce Announce this issue on triage meeting label Sep 10, 2026

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