Add expansion info to implied bounds by oli-obk · Pull Request #157702 · rust-lang/rust

oli-obk · 2026-06-10T11:37:43Z

cc @davidtwco for implied bound diagnostics

We used to have various fun ways for testing whether a Sized bound was implicit or not (usually by checking if the span was equal to the span of a generic parameter). That felt a bit hacky, so I checked what happens if we explicitly mark the span as being desugared. Turns out a lot of diagnostics break. You can see in the diff where I changed things to make them work again.

Then it became clear that we were missing out on various other implied bound sites, and we just got all of them basically for free now.

I think there are various other good refactorings we can do (probably not special casing Sized and not special casing implied bound desugarings, but just reporting all desugarings), but for now this PR is in a state where I'd rather merge it than add more to it

rustbot · 2026-06-10T11:37:46Z

HIR ty lowering was modified

cc @fmease

davidtwco

r=me whether you'd like to apply the suggestion or not

View changes since this review

estebank

+ r=me on these changes.

View changes since this review

estebank · 2026-06-12T22:59:12Z

   |        ^ unused type parameter
   |
   = help: consider removing `N` or referring to it in the body of the type alias
-   = help: if you intended `N` to be a const parameter, use `const N: /* Type */` instead


Interesting to see this go away, didn't really catch which change caused that.

It's odd given that check_type_alias_type_params_are_used was indeed updated to no longer use the old "bound.span == param.span" check.

Considering N has an explicit ?Sized bound, it makes sense not to suggest turning it into a const. This is another improvement from this PR's change.

The change was intentional, that logic was checking whether there were any bounds that aren't implicit default bounds.

rustbot · 2026-06-16T13:57:34Z

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.

oli-obk · 2026-06-16T13:57:38Z

@bors r=davidtwco,estebank

rust-bors · 2026-06-16T13:57:41Z

📌 Commit 16c1bf4 has been approved by davidtwco,estebank

It is now in the queue for this repository.

@estebank

…info, r=davidtwco,estebank Add expansion info to implied bounds r? @estebank maybe? cc @davidtwco for implied bound diagnostics We used to have various fun ways for testing whether a `Sized` bound was implicit or not (usually by checking if the span was equal to the span of a generic parameter). That felt a bit hacky, so I checked what happens if we explicitly mark the span as being desugared. Turns out a lot of diagnostics break. You can see in the diff where I changed things to make them work again. Then it became clear that we were missing out on various other implied bound sites, and we just got all of them basically for free now. I think there are various other good refactorings we can do (probably not special casing `Sized` and not special casing implied bound desugarings, but just reporting all desugarings), but for now this PR is in a state where I'd rather merge it than add more to it

…uwer Rollup of 10 pull requests Successful merges: - #155535 (export symbols: support macos/windows(32/64)) - #156538 (Refactor `AliasTy`. `AliasTerm` & `UnevaluatedConst` to use `Alias`) - #156807 (Add `T: PartialEq` bounds to derived `StructuralPartialEq` impls.) - #156950 (Staticlib rename internal symbols) - #157702 (Add expansion info to implied bounds) - #155616 (constify `TryFrom<Vec>` for array) - #156226 (diagnostics: point to coroutine body on higher-ranked auto trait errors) - #157873 (mips: set llvm_args -mno-check-zero-division for all mips targets) - #157953 (fix(rustc_codegen_ssa): Use cg_operand for Freeze check) - #157958 (doc: Document `-Zlint-rust-version`)

@estebank

…info, r=davidtwco,estebank Add expansion info to implied bounds r? @estebank maybe? cc @davidtwco for implied bound diagnostics We used to have various fun ways for testing whether a `Sized` bound was implicit or not (usually by checking if the span was equal to the span of a generic parameter). That felt a bit hacky, so I checked what happens if we explicitly mark the span as being desugared. Turns out a lot of diagnostics break. You can see in the diff where I changed things to make them work again. Then it became clear that we were missing out on various other implied bound sites, and we just got all of them basically for free now. I think there are various other good refactorings we can do (probably not special casing `Sized` and not special casing implied bound desugarings, but just reporting all desugarings), but for now this PR is in a state where I'd rather merge it than add more to it

…uwer Rollup of 13 pull requests Successful merges: - #156538 (Refactor `AliasTy`. `AliasTerm` & `UnevaluatedConst` to use `Alias`) - #156807 (Add `T: PartialEq` bounds to derived `StructuralPartialEq` impls.) - #156950 (Staticlib rename internal symbols) - #156983 (Add `io::Read::read_le` and `io::Read::read_be`) - #157306 (tests: codegen-llvm: Expect the new mangling scheme in bpf-abi-indirect-return) - #157702 (Add expansion info to implied bounds) - #155616 (constify `TryFrom<Vec>` for array) - #156226 (diagnostics: point to coroutine body on higher-ranked auto trait errors) - #157870 (std: sys: solid: clamp connect_timeout tv_sec instead of truncating) - #157952 (Configure Renovate for GitHub Actions) - #157953 (fix(rustc_codegen_ssa): Use cg_operand for Freeze check) - #157958 (doc: Document `-Zlint-rust-version`) - #157974 (Rename `errors.rs` file to `diagnostics.rs` (11/N))

…nfo, r=davidtwco,estebank" This reverts commit 18509d2, reversing changes made to bf0dfb6.

JonathanBrouwer · 2026-06-19T08:52:45Z

This PR caused a significant perf regression in this rollup #157991
Because of the perf infastructure borking this was a bit hard to diagnose, had to locally bisect. Will verify in a revert PR that I correctly bisected: #158122
Any ideas what caused this? Can we fix this?

JonathanBrouwer · 2026-06-19T10:44:03Z

Also caused an ICE #158093
Let's revert this PR for now, as per https://forge.rust-lang.org/compiler/reviews.html#reverts

If a merged PR is found to have caused a meaningful unanticipated regression, the best policy is to revert it quickly and re-land it later once a fix and regression test are added.

@oli-obk

…thanBrouwer Revert "Add expansion info to implied bounds" This reverts PR #157702 because it causes an ICE and a significant perf regression. This PR also adds a regression test for the ICE. r? ghost cc @oli-obk @estebank @davidtwco Fixes #158093

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. labels Jun 10, 2026

rustbot assigned estebank Jun 10, 2026

davidtwco approved these changes Jun 12, 2026

View reviewed changes

Comment thread compiler/rustc_span/src/hygiene.rs Outdated

estebank approved these changes Jun 12, 2026

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oli-obk added 4 commits June 16, 2026 10:40

Generalize where bound handling

52ed05c

Exhaustively match on DesugaringKind

9abb8ac

Add expansion info to default bounds

d3c8318

Add expansion info to assoc type default bounds

16c1bf4

oli-obk force-pushed the having-fun-with-expansion-info branch from 44d45cf to 16c1bf4 Compare June 16, 2026 13:57

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 Jun 16, 2026

JonathanBrouwer mentioned this pull request Jun 16, 2026

Rollup of 10 pull requests #157975

Closed

This was referenced Jun 16, 2026

Rollup of 12 pull requests #157981

Closed

Rollup of 13 pull requests #157991

Merged

rust-bors Bot merged commit 18509d2 into rust-lang:main Jun 16, 2026
13 checks passed

rustbot added this to the 1.98.0 milestone Jun 16, 2026

JonathanBrouwer mentioned this pull request Jun 19, 2026

Revert "Add expansion info to implied bounds" #158122

Open

rust-bors Bot pushed a commit that referenced this pull request Jun 19, 2026

Revert "Rollup merge of #157702 - oli-obk:having-fun-with-expansion-i…

0676d2e

…nfo, r=davidtwco,estebank" This reverts commit 18509d2, reversing changes made to bf0dfb6.

apiraino mentioned this pull request Jun 19, 2026

[ICE]: Found unstable fingerprints for explicit_supertraits_containing_assoc_item #158093

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Add expansion info to implied bounds#157702

Add expansion info to implied bounds#157702
rust-bors[bot] merged 4 commits into
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oli-obk:having-fun-with-expansion-info

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