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fix: dedup static_candidates before report #111872

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May 30, 2023
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fix: dedup static_candidates before report #111872

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6 changes: 6 additions & 0 deletions compiler/rustc_hir_typeck/src/method/suggest.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -473,6 +473,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
let mut custom_span_label = false;

let static_candidates = &mut no_match_data.static_candidates;

// `static_candidates` may have same candidates appended by
// inherent and extension, which may result in incorrect
// diagnostic.
static_candidates.dedup();
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Could you add a comment why we cannot remove the duplicated call to record_static_candidate?

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inherent and extension may append the same item to static_candidates.

For example:

trait Cat {
    fn nya() {}
}

fn uwu<T: Cat>(c: T) {
    c.nya();
}

Both <T as Cat> (inherent) and <_ as Cat> (extension) had been tried.

And another:

trait Cat {
    fn nya() {}
}

fn uwu<T>(c: T) {
    c.nya();
}

<_ as Cat> (extension) should be tried.

Therefore, we can't remove duplicated call of record_static_candidate.

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The comment you added says that in order to improve the diagnostic, we record both inherent and extension cases. But this PR does the opposite: we deduplicate to improve the diagnostic.
You don't need to link to the PR. The 2 lines-long explanation is enough.

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I have two questions:

  1. Is it correct to say that we cannot remove the duplicated call of record_static_candidate? Also, is it intended behavior that the unexpected diagnostic of Unhelpful help when calling associated trait function as method #103646 was caused by invoking record_static_candidate for the same item in both assemble_extension_candidates_for_trait and assemble_inherent_impl_probe?
  2. Is static_candidates.dedup() the right approach here? If this statement has too broad impact, can we change the condition to !self.has_applicable_self(&item) && !self.static_candidates.contains(&item) in extension_candidates?


if !static_candidates.is_empty() {
err.note(
"found the following associated functions; to be used as methods, \
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11 changes: 11 additions & 0 deletions tests/ui/suggestions/issue-103646.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
trait Cat {
fn nya() {}
}

fn uwu<T: Cat>(c: T) {
c.nya();
//~^ ERROR no method named `nya` found for type parameter `T` in the current scope
//~| Suggestion T::nya()
}

fn main() {}
21 changes: 21 additions & 0 deletions tests/ui/suggestions/issue-103646.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,21 @@
error[E0599]: no method named `nya` found for type parameter `T` in the current scope
--> $DIR/issue-103646.rs:6:7
|
LL | fn uwu<T: Cat>(c: T) {
| - method `nya` not found for this type parameter
LL | c.nya();
| --^^^--
| | |
| | this is an associated function, not a method
| help: use associated function syntax instead: `T::nya()`
|
= note: found the following associated functions; to be used as methods, functions must have a `self` parameter
note: the candidate is defined in the trait `Cat`
--> $DIR/issue-103646.rs:2:5
|
LL | fn nya() {}
| ^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0599`.