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Rollup merge of #121100 - estebank:issue-71252, r=compiler-errors

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Detect when method call on argument could be removed to fulfill failed trait bound

When encountering

```rust
struct Foo;
struct Bar;
impl From<Bar> for Foo {
    fn from(_: Bar) -> Self { Foo }
}
fn qux(_: impl From<Bar>) {}
fn main() {
    qux(Bar.into());
}
```

Suggest removing `.into()`:

```
error[E0283]: type annotations needed
 --> f100.rs:8:13
  |
8 |     qux(Bar.into());
  |     ---     ^^^^
  |     |
  |     required by a bound introduced by this call
  |
  = note: cannot satisfy `_: From<Bar>`
note: required by a bound in `qux`
 --> f100.rs:6:16
  |
6 | fn qux(_: impl From<Bar>) {}
  |                ^^^^^^^^^ required by this bound in `qux`
help: try using a fully qualified path to specify the expected types
  |
8 |     qux(<Bar as Into<T>>::into(Bar));
  |         +++++++++++++++++++++++   ~
help: consider removing this method call, as the receiver has type `Bar` and `Bar: From<Bar>` trivially holds
  |
8 -     qux(Bar.into());
8 +     qux(Bar);
  |
```

Fix #71252
This commit is contained in:
León Orell Valerian Liehr 2024-02-18 05:10:16 +01:00 • committed by GitHub
commit 6499eb5577
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6 changed files with 72 additions and 1 deletions
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20
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
View file

@ -3689,6 +3689,24 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
if let Node::Expr(expr) = tcx.hir_node(arg_hir_id)
&& let Some(typeck_results) = &self.typeck_results
{
if let hir::Expr { kind: hir::ExprKind::MethodCall(_, rcvr, _, _), .. } = expr
&& let Some(ty) = typeck_results.node_type_opt(rcvr.hir_id)
&& let Some(failed_pred) = failed_pred.to_opt_poly_trait_pred()
&& let pred = failed_pred.map_bound(|pred| pred.with_self_ty(tcx, ty))
&& self.predicate_must_hold_modulo_regions(&Obligation::misc(
tcx, expr.span, body_id, param_env, pred,
))
{
err.span_suggestion_verbose(
expr.span.with_lo(rcvr.span.hi()),
format!(
"consider removing this method call, as the receiver has type `{ty}` and \
`{pred}` trivially holds",
),
"",
Applicability::MaybeIncorrect,
);
}
if let hir::Expr { kind: hir::ExprKind::Block(block, _), .. } = expr {
let inner_expr = expr.peel_blocks();
let ty = typeck_results
@ -3824,7 +3842,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
}
}
if let Node::Expr(expr) = tcx.hir_node(call_hir_id) {
if let Node::Expr(expr) = call_node {
if let hir::ExprKind::Call(hir::Expr { span, .. }, _)
| hir::ExprKind::MethodCall(
hir::PathSegment { ident: Ident { span, .. }, .. },