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Rollup merge of #156796 - Kokoro2336:fix/match-str-sugg, r=estebank

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Fix missing suggestion when matching `String` with `&str`

Fixes rust-lang/rust#156404

Add suggestion when matching `String` with `&str`
This commit is contained in:
Jonathan Brouwer
2026-05-27 08:14:24 +02:00
committed by GitHub
parent d1fc603d17 a09204ad18
commit 495657cc2a
5 changed files with 100 additions and 1 deletions
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compiler/rustc_hir_typeck/src/pat.rs
+16 -1
View File
@@ -1007,7 +1007,22 @@ fn check_pat_lit(
//
// then that's equivalent to there existing a LUB.
let cause = self.pattern_cause(ti, span);
if let Err(err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
if let Err(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
// If scrutinee is String and pattern is &str, suggest .as_str()
let expected = self.resolve_vars_with_obligations(expected);
if let ty::Adt(adt, _) = expected.kind()
&& self.tcx.is_lang_item(adt.did(), LangItem::String)
&& pat_ty.is_ref()
&& pat_ty.peel_refs().is_str()
&& let Some(origin_expr) = ti.origin_expr
{
err.span_suggestion_verbose(
origin_expr.span.shrink_to_hi(),
"consider converting the `String` to a `&str` using `.as_str()`",
".as_str()",
Applicability::MachineApplicable,
);
}
err.emit();
}
tests/ui/pattern/deref-patterns/needs-gate.stderr
+5
View File
@@ -76,6 +76,11 @@ LL | match "str".to_owned() {
| ---------------- this expression has type `String`
LL | "str" => {}
| ^^^^^ expected `String`, found `&str`
|
help: consider converting the `String` to a `&str` using `.as_str()`
|
LL | match "str".to_owned().as_str() {
| +++++++++
error[E0308]: mismatched types
--> $DIR/needs-gate.rs:52:12
tests/ui/pattern/string-match-as-str-suggestion.fixed
+18
View File
@@ -0,0 +1,18 @@
//@ run-rustfix
fn main() {
let s = "yes".to_owned();
let _ = match s.as_str() {
"yes" => Some(true),
//~^ ERROR mismatched types
"no" => Some(false),
//~^ ERROR mismatched types
_ => None,
};
let s2 = String::from("hello");
if let "hello" = s2.as_str() {
//~^ ERROR mismatched types
}
}
tests/ui/pattern/string-match-as-str-suggestion.rs
+18
View File
@@ -0,0 +1,18 @@
//@ run-rustfix
fn main() {
let s = "yes".to_owned();
let _ = match s {
"yes" => Some(true),
//~^ ERROR mismatched types
"no" => Some(false),
//~^ ERROR mismatched types
_ => None,
};
let s2 = String::from("hello");
if let "hello" = s2 {
//~^ ERROR mismatched types
}
}
tests/ui/pattern/string-match-as-str-suggestion.stderr
+43
View File
@@ -0,0 +1,43 @@
error[E0308]: mismatched types
--> $DIR/string-match-as-str-suggestion.rs:7:9
|
LL | let _ = match s {
| - this expression has type `String`
LL | "yes" => Some(true),
| ^^^^^ expected `String`, found `&str`
|
help: consider converting the `String` to a `&str` using `.as_str()`
|
LL | let _ = match s.as_str() {
| +++++++++
error[E0308]: mismatched types
--> $DIR/string-match-as-str-suggestion.rs:9:9
|
LL | let _ = match s {
| - this expression has type `String`
...
LL | "no" => Some(false),
| ^^^^ expected `String`, found `&str`
|
help: consider converting the `String` to a `&str` using `.as_str()`
|
LL | let _ = match s.as_str() {
| +++++++++
error[E0308]: mismatched types
--> $DIR/string-match-as-str-suggestion.rs:15:12
|
LL | if let "hello" = s2 {
| ^^^^^^^ -- this expression has type `String`
| |
| expected `String`, found `&str`
|
help: consider converting the `String` to a `&str` using `.as_str()`
|
LL | if let "hello" = s2.as_str() {
| +++++++++
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0308`.