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Merged
rust-bors merged 1 commit into from
Jan 15, 2026
Merged

Recover parse gracefully from <const N> #151099

rust-bors merged 1 commit into from
Jan 15, 2026
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@estebank estebank commented Jan 14, 2026 •
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When a const param doesn't have a : Type, recover the parser state and provide a structured suggestion. This not only provides guidance on what was missing, but it also makes subsuequent errors to be emitted that would otherwise be silenced.

error: expected `:`, found `>`
  --> $DIR/incorrect-const-param.rs:26:16
   |
LL | impl<T, const N> From<[T; N]> for VecWrapper<T>
   |                ^ expected `:`
   |
help: you might have meant to write the type of the const parameter here
   |
LL | impl<T, const N: /* Type */> From<[T; N]> for VecWrapper<T>
   |                ++++++++++++

r? @fmease

Follow up to #151077. Fix #84327.

@rustbot 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 Jan 14, 2026
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@estebank
Recover parse gracefully from <const N>
92db7b2 
When a const param doesn't have a `: Type`, recover the parser state and provide a structured suggestion. This not only provides guidance on what was missing, but it also makes subsuequent errors to be emitted that would otherwise be silenced.

```
error: expected `:`, found `>`
  --> $DIR/incorrect-const-param.rs:26:16
   |
LL | impl<T, const N> From<[T; N]> for VecWrapper<T>
   |                ^ expected `:`
   |
help: you might have meant to write the type of the const parameter here
   |
LL | impl<T, const N: /* Type */> From<[T; N]> for VecWrapper<T>
   |                ++++++++++++
```
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rustbot commented Jan 14, 2026

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.

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Nice, thanks! r=me rollup with nitpick addressed in one way or another

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tests/ui/const-generics/incorrect-const-param.rs
@@ -0,0 +1,45 @@
// #84327
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I get that it's nice to group all 3 cases from the issue but is it really necessary? We already have tests in separate files for the other 2 cases we've already addressed (in your PR: #151077, and in mine: #120570).

This doesn't increase test coverage unless I've missed sth. and the added test cases exercise things the preexisting tests don't.

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It exercises that the parser recovers correctly besides just providing the suggestion. I tend to group related checks either in the same file when possible, or with files with similar naming. I considered only having this case in the test and then a type error, but felt that having all of them (even if redundant because individual cases are already tested) would help in the future if someone makes changes that incidentally touches these to notice that there are similarly handled cases.

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estebank commented Jan 14, 2026

@bors r=fmease

@rust-bors 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 Jan 14, 2026
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rust-bors bot commented Jan 14, 2026

📌 Commit 92db7b2 has been approved by fmease

It is now in the queue for this repository.

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fmease commented Jan 14, 2026

@bors rollup

JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Jan 14, 2026
@JonathanBrouwer
Rollup merge of rust-lang#151099 - issue-84327-2, r=fmease
4826ff1 
Recover parse gracefully from `<const N>`

When a const param doesn't have a `: Type`, recover the parser state and provide a structured suggestion. This not only provides guidance on what was missing, but it also makes subsuequent errors to be emitted that would otherwise be silenced.

```
error: expected `:`, found `>`
  --> $DIR/incorrect-const-param.rs:26:16
   |
LL | impl<T, const N> From<[T; N]> for VecWrapper<T>
   |                ^ expected `:`
   |
help: you might have meant to write the type of the const parameter here
   |
LL | impl<T, const N: /* Type */> From<[T; N]> for VecWrapper<T>
   |                ++++++++++++
```

r? @fmease

Follow up to rust-lang#151077. Fix rust-lang#84327.
@JonathanBrouwer JonathanBrouwer mentioned this pull request Jan 14, 2026
Closed
rust-bors bot pushed a commit that referenced this pull request Jan 14, 2026
@bors
Auto merge of #151139 - JonathanBrouwer:rollup-Zi3DAdq, r=JonathanBro…
cf3684a 
…uwer

Rollup of 16 pull requests

Successful merges:

 - #150585 (Add a context-consistency check before emitting redundant generic-argument suggestions)
 - #150586 (rustdoc: Fix intra-doc link bugs involving type aliases and associated items)
 - #150590 (Don't try to recover keyword as non-keyword identifier )
 - #150817 (cleanup: remove borrowck handling for inline const patterns)
 - #150939 (resolve: Relax some asserts in glob overwriting and add tests)
 - #150962 (Remove `FeedConstTy` and provide ty when lowering const arg)
 - #150966 (rustc_target: Remove unused Arch::PowerPC64LE)
 - #150971 (Disallow eii in statement position)
 - #151016 (fix: WASI threading regression by disabling pthread usage)
 - #151046 (compiler: Make Externally Implementable Item (eii) macros "semiopaque")
 - #151099 (Recover parse gracefully from `<const N>`)
 - #151117 (Avoid serde dependency in build_helper when not necessary)
 - #151127 (Delete `MetaItemOrLitParser::Err`)
 - #151128 (Add temporary new bors e-mail address to the mailmap)
 - #151130 (resolve: Downgrade `ambiguous_glob_imports` to warn-by-default)
 - #151138 (Rename `rust.use-lld` to `rust.bootstrap-override-lld` in INSTALL.md)

r? @ghost
@JonathanBrouwer JonathanBrouwer mentioned this pull request Jan 14, 2026
Merged
rust-bors bot pushed a commit that referenced this pull request Jan 14, 2026
@bors
Auto merge of #151144 - JonathanBrouwer:rollup-QW4Ug5q, r=JonathanBro…
b6fdaf2 
…uwer

Rollup of 15 pull requests

Successful merges:

 - #150585 (Add a context-consistency check before emitting redundant generic-argument suggestions)
 - #150586 (rustdoc: Fix intra-doc link bugs involving type aliases and associated items)
 - #150590 (Don't try to recover keyword as non-keyword identifier )
 - #150817 (cleanup: remove borrowck handling for inline const patterns)
 - #150939 (resolve: Relax some asserts in glob overwriting and add tests)
 - #150962 (Remove `FeedConstTy` and provide ty when lowering const arg)
 - #150966 (rustc_target: Remove unused Arch::PowerPC64LE)
 - #150971 (Disallow eii in statement position)
 - #151016 (fix: WASI threading regression by disabling pthread usage)
 - #151046 (compiler: Make Externally Implementable Item (eii) macros "semiopaque")
 - #151099 (Recover parse gracefully from `<const N>`)
 - #151117 (Avoid serde dependency in build_helper when not necessary)
 - #151127 (Delete `MetaItemOrLitParser::Err`)
 - #151128 (Add temporary new bors e-mail address to the mailmap)
 - #151138 (Rename `rust.use-lld` to `rust.bootstrap-override-lld` in INSTALL.md)

r? @ghost
@rust-bors rust-bors bot merged commit 00501de into rust-lang:main Jan 15, 2026
11 checks passed
@rustbot rustbot added this to the 1.94.0 milestone Jan 15, 2026
rust-timer added a commit that referenced this pull request Jan 15, 2026
@rust-timer
Unrolled build for #151099
e50e1aa 
Rollup merge of #151099 - issue-84327-2, r=fmease

Recover parse gracefully from `<const N>`

When a const param doesn't have a `: Type`, recover the parser state and provide a structured suggestion. This not only provides guidance on what was missing, but it also makes subsuequent errors to be emitted that would otherwise be silenced.

```
error: expected `:`, found `>`
  --> $DIR/incorrect-const-param.rs:26:16
   |
LL | impl<T, const N> From<[T; N]> for VecWrapper<T>
   |                ^ expected `:`
   |
help: you might have meant to write the type of the const parameter here
   |
LL | impl<T, const N: /* Type */> From<[T; N]> for VecWrapper<T>
   |                ++++++++++++
```

r? @fmease

Follow up to #151077. Fix #84327.
github-actions bot pushed a commit to rust-lang/miri that referenced this pull request Jan 15, 2026
@bors
Auto merge of #151144 - JonathanBrouwer:rollup-QW4Ug5q, r=JonathanBro…
f982e90 
…uwer

Rollup of 15 pull requests

Successful merges:

 - rust-lang/rust#150585 (Add a context-consistency check before emitting redundant generic-argument suggestions)
 - rust-lang/rust#150586 (rustdoc: Fix intra-doc link bugs involving type aliases and associated items)
 - rust-lang/rust#150590 (Don't try to recover keyword as non-keyword identifier )
 - rust-lang/rust#150817 (cleanup: remove borrowck handling for inline const patterns)
 - rust-lang/rust#150939 (resolve: Relax some asserts in glob overwriting and add tests)
 - rust-lang/rust#150962 (Remove `FeedConstTy` and provide ty when lowering const arg)
 - rust-lang/rust#150966 (rustc_target: Remove unused Arch::PowerPC64LE)
 - rust-lang/rust#150971 (Disallow eii in statement position)
 - rust-lang/rust#151016 (fix: WASI threading regression by disabling pthread usage)
 - rust-lang/rust#151046 (compiler: Make Externally Implementable Item (eii) macros "semiopaque")
 - rust-lang/rust#151099 (Recover parse gracefully from `<const N>`)
 - rust-lang/rust#151117 (Avoid serde dependency in build_helper when not necessary)
 - rust-lang/rust#151127 (Delete `MetaItemOrLitParser::Err`)
 - rust-lang/rust#151128 (Add temporary new bors e-mail address to the mailmap)
 - rust-lang/rust#151138 (Rename `rust.use-lld` to `rust.bootstrap-override-lld` in INSTALL.md)

r? @ghost
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Provide const generics hints when a token is forgotten

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