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Rollup merge of #92715 - chordtoll:empty-string, r=davidtwco

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Do not suggest char literal for zero-length strings

PR #92507 adds a hint to switch to single quotes when a char is expected and a single-character string literal is provided.

The check to ensure the string literal is one character long missed the 0-char case, and would incorrectly offer the hint.

This PR adds the missing check, and a test case to confirm the new behavior.
This commit is contained in:
Matthias Krüger 2022-02-08 16:40:47 +01:00 • committed by GitHub
commit 8429dcdb79
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3 changed files with 12 additions and 3 deletions
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2
compiler/rustc_infer/src/infer/error_reporting/mod.rs
View file

@ -2053,7 +2053,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
if let Some(code) = if let Some(code) =
code.strip_prefix('"').and_then(|s| s.strip_suffix('"')) code.strip_prefix('"').and_then(|s| s.strip_suffix('"'))
{ {
if code.chars().nth(1).is_none() { if code.chars().count() == 1 {
err.span_suggestion( err.span_suggestion(
span, span,
"if you meant to write a `char` literal, use single quotes", "if you meant to write a `char` literal, use single quotes",

3
src/test/ui/inference/char-as-str-multi.rs
View file

@ -1,6 +1,7 @@
// When a MULTI-character string literal is used where a char should be, // When a MULTI/NO-character string literal is used where a char should be,
// DO NOT suggest changing to single quotes. // DO NOT suggest changing to single quotes.
fn main() { fn main() {
let _: char = "foo"; //~ ERROR mismatched types let _: char = "foo"; //~ ERROR mismatched types
let _: char = ""; //~ ERROR mismatched types
} }

10
src/test/ui/inference/char-as-str-multi.stderr
View file

@ -6,6 +6,14 @@ LL | let _: char = "foo";
| | | |
| expected due to this | expected due to this
error: aborting due to previous error error[E0308]: mismatched types
--> $DIR/char-as-str-multi.rs:6:19
|
LL | let _: char = "";
| ---- ^^ expected `char`, found `&str`
| |
| expected due to this
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0308`. For more information about this error, try `rustc --explain E0308`.