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>` can be fulfilled
|
8 - qux(Bar.into());
8 + qux(Bar);
|
```
Fix #71252
This commit is contained in:
@@ -3961,6 +3961,24 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
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if let Node::Expr(expr) = tcx.hir_node(arg_hir_id)
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&& let Some(typeck_results) = &self.typeck_results
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{
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if let hir::Expr { kind: hir::ExprKind::MethodCall(_, rcvr, _, _), .. } = expr
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&& let Some(ty) = typeck_results.node_type_opt(rcvr.hir_id)
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&& let Some(failed_pred) = failed_pred.to_opt_poly_trait_pred()
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&& let pred = failed_pred.map_bound(|pred| pred.with_self_ty(tcx, ty))
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&& self.predicate_must_hold_modulo_regions(&Obligation::misc(
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tcx, expr.span, body_id, param_env, pred,
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))
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{
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err.span_suggestion_verbose(
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expr.span.with_lo(rcvr.span.hi()),
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format!(
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"consider removing this method call, as the receiver has type `{ty}` and \
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`{pred}` trivially holds",
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),
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"",
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Applicability::MaybeIncorrect,
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);
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}
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if let hir::Expr { kind: hir::ExprKind::Block(block, _), .. } = expr {
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let inner_expr = expr.peel_blocks();
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let ty = typeck_results
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@@ -4096,7 +4114,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
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}
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}
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if let Node::Expr(expr) = tcx.hir_node(call_hir_id) {
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if let Node::Expr(expr) = call_node {
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if let hir::ExprKind::Call(hir::Expr { span, .. }, _)
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| hir::ExprKind::MethodCall(
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hir::PathSegment { ident: Ident { span, .. }, .. },
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