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Tweak fn pointer suggestion span #136412

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merged 1 commit into from
Feb 2, 2025

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estebank
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@estebank estebank commented Feb 2, 2025

Use a more targeted span when suggesting casting an fn item to an fn pointer.

error[E0308]: cannot coerce functions which must be inlined to function pointers
  --> $DIR/cast.rs:10:33
   |
LL |     let _: fn(isize) -> usize = callee;
   |            ------------------   ^^^^^^ cannot coerce functions which must be inlined to function pointers
   |            |
   |            expected due to this
   |
   = note: expected fn pointer `fn(_) -> _`
                 found fn item `fn(_) -> _ {callee}`
   = note: fn items are distinct from fn pointers
help: consider casting to a fn pointer
   |
LL |     let _: fn(isize) -> usize = callee as fn(isize) -> usize;
   |                                        +++++++++++++++++++++
error[E0308]: mismatched types
  --> $DIR/fn-pointer-mismatch.rs:42:30
   |
LL |     let d: &fn(u32) -> u32 = foo;
   |            ---------------   ^^^ expected `&fn(u32) -> u32`, found fn item
   |            |
   |            expected due to this
   |
   = note: expected reference `&fn(_) -> _`
                found fn item `fn(_) -> _ {foo}`
help: consider using a reference
   |
LL |     let d: &fn(u32) -> u32 = &foo;
   |                              +

Previously we'd point at the whole expression for replacement, instead of marking what was being added.

We could also modify the suggestions for &(name as fn()), but for that we require storing more accurate spans than we have now.

Use a more targeted span when suggesting casting an `fn` item to an `fn` pointer.

```
error[E0308]: cannot coerce functions which must be inlined to function pointers
  --> $DIR/cast.rs:10:33
   |
LL |     let _: fn(isize) -> usize = callee;
   |            ------------------   ^^^^^^ cannot coerce functions which must be inlined to function pointers
   |            |
   |            expected due to this
   |
   = note: expected fn pointer `fn(_) -> _`
                 found fn item `fn(_) -> _ {callee}`
   = note: fn items are distinct from fn pointers
help: consider casting to a fn pointer
   |
LL |     let _: fn(isize) -> usize = callee as fn(isize) -> usize;
   |                                        +++++++++++++++++++++
```
```
error[E0308]: mismatched types
  --> $DIR/fn-pointer-mismatch.rs:42:30
   |
LL |     let d: &fn(u32) -> u32 = foo;
   |            ---------------   ^^^ expected `&fn(u32) -> u32`, found fn item
   |            |
   |            expected due to this
   |
   = note: expected reference `&fn(_) -> _`
                found fn item `fn(_) -> _ {foo}`
help: consider using a reference
   |
LL |     let d: &fn(u32) -> u32 = &foo;
   |                              +
```
Previously we'd point at the whole expression for replacement, instead of marking what was being added.

We could also modify the suggestions for `&(name as fn())`, but for that we require storing more accurate spans than we have now.
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rustbot commented Feb 2, 2025

r? @petrochenkov

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@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 Feb 2, 2025
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Thanks

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jieyouxu commented Feb 2, 2025

r? jieyouxu @bors r+ rollup

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bors commented Feb 2, 2025

📌 Commit 028a920 has been approved by jieyouxu

It is now in the queue for this repository.

@bors bors 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 Feb 2, 2025
bors added a commit to rust-lang-ci/rust that referenced this pull request Feb 2, 2025
…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#133266 (ci: fix explanation why LLVM download is disabled for windows-gnu)
 - rust-lang#136133 (Fix sentence in process::abort)
 - rust-lang#136279 (Rename `tcx.ensure()` to `tcx.ensure_ok()`, and improve the associated docs)
 - rust-lang#136328 (Rework "long type names" printing logic)
 - rust-lang#136358 (`#[optimize(none)]` implies `#[inline(never)]`)
 - rust-lang#136368 (Make comma separated lists of anything easier to make for errors)
 - rust-lang#136412 (Tweak fn pointer suggestion span)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 44def58 into rust-lang:master Feb 2, 2025
6 checks passed
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Feb 2, 2025
Rollup merge of rust-lang#136412 - estebank:fn-ptr-cast-suggestion, r=jieyouxu

Tweak fn pointer suggestion span

Use a more targeted span when suggesting casting an `fn` item to an `fn` pointer.

```
error[E0308]: cannot coerce functions which must be inlined to function pointers
  --> $DIR/cast.rs:10:33
   |
LL |     let _: fn(isize) -> usize = callee;
   |            ------------------   ^^^^^^ cannot coerce functions which must be inlined to function pointers
   |            |
   |            expected due to this
   |
   = note: expected fn pointer `fn(_) -> _`
                 found fn item `fn(_) -> _ {callee}`
   = note: fn items are distinct from fn pointers
help: consider casting to a fn pointer
   |
LL |     let _: fn(isize) -> usize = callee as fn(isize) -> usize;
   |                                        +++++++++++++++++++++
```
```
error[E0308]: mismatched types
  --> $DIR/fn-pointer-mismatch.rs:42:30
   |
LL |     let d: &fn(u32) -> u32 = foo;
   |            ---------------   ^^^ expected `&fn(u32) -> u32`, found fn item
   |            |
   |            expected due to this
   |
   = note: expected reference `&fn(_) -> _`
                found fn item `fn(_) -> _ {foo}`
help: consider using a reference
   |
LL |     let d: &fn(u32) -> u32 = &foo;
   |                              +
```
Previously we'd point at the whole expression for replacement, instead of marking what was being added.

We could also modify the suggestions for `&(name as fn())`, but for that we require storing more accurate spans than we have now.
@rustbot rustbot added this to the 1.86.0 milestone Feb 2, 2025
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5 participants