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Emit a suggestion to cast the never type into a concrete type when it fails to satisfy an impl Trait bound#157966

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Muhtasim-Rasheed:issue-157923-suggestion-cast-never-type
Jul 6, 2026
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Emit a suggestion to cast the never type into a concrete type when it fails to satisfy an impl Trait bound#157966
rust-bors[bot] merged 1 commit into
rust-lang:mainfrom
Muhtasim-Rasheed:issue-157923-suggestion-cast-never-type

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@Muhtasim-Rasheed

@Muhtasim-Rasheed Muhtasim-Rasheed commented Jun 16, 2026 •
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Fixes #157923

@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 Jun 16, 2026
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r? @mati865

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qaijuang
qaijuang reviewed Jun 16, 2026
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@qaijuang qaijuang left a comment •
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Took a quick glance 👀

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Comment thread compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs Outdated
Comment on lines +4490 to +4496
let snippet = tcx.sess.source_map().span_to_snippet(span).unwrap();
if span != expr.span {
err.help(format!(
"`!` can be coerced to any type; consider casting to a concrete type that implements the trait, e.g. \
`{} as SomeType`", snippet
));
}

@qaijuang qaijuang Jun 16, 2026

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Suggested change
let snippet = tcx.sess.source_map().span_to_snippet(span).unwrap();
if span != expr.span {
err.help(format!(
"`!` can be coerced to any type; consider casting to a concrete type that implements the trait, e.g. \
`{} as SomeType`", snippet
));
}
if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(span)
&& span != expr.span
{
err.help(format!(
"`!` can be coerced to any type; consider casting to a concrete type that implements the trait, e.g. \
`{snippet} as SomeType`"
));
}

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mati865 commented Jun 17, 2026

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@rustbot reroll

@rustbot rustbot assigned davidtwco and unassigned mati865 Jun 17, 2026
davidtwco
davidtwco requested changes Jul 2, 2026
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This seems reasonable to me, one comment

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Comment thread compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs Outdated
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 2, 2026
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Reminder, once the PR becomes ready for a review, use @rustbot ready.

@Muhtasim-Rasheed Muhtasim-Rasheed force-pushed the issue-157923-suggestion-cast-never-type branch from e0182f3 to c9ad0e5 Compare July 5, 2026 13:56
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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.

@Muhtasim-Rasheed

Muhtasim-Rasheed commented Jul 5, 2026

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@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 5, 2026
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davidtwco commented Jul 6, 2026

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@bors r+ rollup

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📌 Commit c9ad0e5 has been approved by davidtwco

It is now in the queue for this repository.

@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 Jul 6, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Jul 6, 2026
@JonathanBrouwer
Rollup merge of rust-lang#157966 - Muhtasim-Rasheed:issue-157923-sugg…
7536d7e 
…estion-cast-never-type, r=davidtwco

Emit a suggestion to cast the never type into a concrete type when it fails to satisfy an `impl Trait` bound

Fixes rust-lang#157923
This was referenced Jul 6, 2026
Closed
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rust-bors Bot pushed a commit that referenced this pull request Jul 6, 2026
@bors
Auto merge of #158864 - JonathanBrouwer:rollup-re2xAGf, r=JonathanBro…
36714a9 
…uwer

Rollup of 12 pull requests

Successful merges:

 - #156976 (enable eager `param_env` norm in new solver)
 - #158537 (Add `std::io::cursor::WriteThroughCursor`)
 - #158540 (Move `std::io::Seek` to `core::io`)
 - #157820 (consider subtyping when checking if an infer var is sized)
 - #158505 (Update POSIX edition links)
 - #158853 (Fix typo for link on nto-qnx.md)
 - #157466 (Better error message when bare type in impl parameter list)
 - #157966 (Emit a suggestion to cast the never type into a concrete type when it fails to satisfy an `impl Trait` bound)
 - #158381 (Expose debug scope of statement and terminator in rustc_public)
 - #158405 (rustc_target: Add ARMv8-M related target features)
 - #158770 (Weaken guarantee for `From<legacy::RangeInclusive> for RangeInclusive`)
 - #158820 (Fix rustdoc ICE on deprecated note in inlined re-export chain)
@rust-bors rust-bors Bot merged commit 1c30ae0 into rust-lang:main Jul 6, 2026
13 checks passed
@rustbot rustbot added this to the 1.99.0 milestone Jul 6, 2026
rust-timer added a commit that referenced this pull request Jul 6, 2026
@rust-timer
Unrolled build for #157966
f7b8674 
Rollup merge of #157966 - Muhtasim-Rasheed:issue-157923-suggestion-cast-never-type, r=davidtwco

Emit a suggestion to cast the never type into a concrete type when it fails to satisfy an `impl Trait` bound

Fixes #157923
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@davidtwco davidtwco davidtwco approved these changes
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Successfully merging this pull request may close these issues.

Emit a suggestion to cast ! to a concrete type when ! is infered as the hidden type for impl Trait and ! doesn't implement Trait

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@Muhtasim-Rasheed @rustbot @mati865 @davidtwco @qaijuang