bjoernager/rust
bjoernager/rust
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Auto merge of #47232 - keatinge:master, r=petrochenkov

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Add help message for incorrect pattern syntax

When I was getting started with rust I often made the mistake of using `||` instead of `|` to match multiple patterns and spent a long time staring at my code wondering what was wrong.

for example:

```
fn main() {
    let x = 1;

    match x {
        1 || 2 => println!("1 or 2"),
        _ => println!("Something else"),
    }
}

```

If you compile this with current rustc you will see

```
error: expected one of `...`, `..=`, `..`, `=>`, `if`, or `|`, found `||`
 --> test.rs:5:11
  |
5 |         1 || 2 => println!("1 or 2"),
  |          -^^ unexpected token
  |          |
  |          expected one of `...`, `..=`, `..`, `=>`, `if`, or `|` here

error: aborting due to previous error
```

With my proposed change it will show:
```
error: unexpected token `||` after pattern
 --> test.rs:5:11
  |
5 |         1 || 2 => println!("1 or 2"),
  |           ^^
  |
  = help: did you mean to use `|` to specify multiple patterns instead?

error: aborting due to previous error
```
This commit is contained in:
bors 2018-01-08 07:11:47 +00:00
commit 1b193de98a
3 changed files with 39 additions and 2 deletions
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16
src/libsyntax/parse/parser.rs
View file

@ -3431,8 +3431,20 @@ impl<'a> Parser<'a> {
let mut pats = Vec::new();
loop {
pats.push(self.parse_pat()?);
if self.check(&token::BinOp(token::Or)) { self.bump();}
else { return Ok(pats); }
if self.token == token::OrOr {
let mut err = self.struct_span_err(self.span,
"unexpected token `||` after pattern");
err.span_suggestion(self.span,
"use a single `|` to specify multiple patterns",
"|".to_owned());
err.emit();
self.bump();
} else if self.check(&token::BinOp(token::Or)) {
self.bump();
} else {
return Ok(pats);
}
};
}