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Error when using catch after try #59847

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Apr 13, 2019
Merged

Error when using catch after try #59847

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4a938b5
Special error when using catch after try
Kampfkarren Apr 10, 2019
de02dd9
Adhere to tidy script
Kampfkarren Apr 10, 2019
2b61431
Fix error brought up by changing tabs to spaces
Kampfkarren Apr 10, 2019
4af7cf3
Fix tests, I think
Kampfkarren Apr 10, 2019
1156ce6
Feedback
Kampfkarren Apr 11, 2019
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10 changes: 9 additions & 1 deletion src/libsyntax/parse/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3618,7 +3618,15 @@ impl<'a> Parser<'a> {
{
let (iattrs, body) = self.parse_inner_attrs_and_block()?;
attrs.extend(iattrs);
Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
if self.eat_keyword(keywords::Catch) {
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@Centril Centril Apr 10, 2019 •
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It would be preferable to ban any form of try { ... } $ident { .. } from a perspective of having maximum flexibility in the future.

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@Kampfkarren Kampfkarren Apr 10, 2019 •
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Should those all suggest match instead, or should that just be catch?

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cc @estebank ^-- I would probably say yes, but that's more a diagnostics issue than future lang design flexibility.

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I'm thinking of the following case:

    let _ = try {
        true
    }
    let _ = ();

where the error is the lack of ;, which is why I'm a bit weary of suggesting the right syntax for every ident. The current output for this the following, which I feel doesn't hinder understanding more than complaining about an inexistent catch would:

error: expected one of `.`, `;`, `?`, or an operator, found `let`
 --> src/main.rs:7:5
  |
6 |     }
  |      - expected one of `.`, `;`, `?`, or an operator here
7 |     let _ = ();
  |     ^^^ unexpected token

let mut error = self.struct_span_err(self.prev_span,
"keyword `catch` cannot follow a `try` block");
error.help("try using `match` on the result of the `try` block instead");
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error.emit();
Err(error)
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} else {
Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
}
}

// `match` token already eaten
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10 changes: 10 additions & 0 deletions src/test/ui/try-block/try-block-catch.rs
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@@ -0,0 +1,10 @@
// compile-flags: --edition 2018

#![feature(try_blocks)]

fn main() {
let res: Option<bool> = try {
true
} catch { };
//~^ ERROR keyword `catch` cannot follow a `try` block
}
10 changes: 10 additions & 0 deletions src/test/ui/try-block/try-block-catch.stderr
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@@ -0,0 +1,10 @@
error: keyword `catch` cannot follow a `try` block
--> $DIR/try-block-catch.rs:8:7
|
LL | } catch { };
| ^^^^^
|
= help: try using `match` on the result of the `try` block instead

error: aborting due to previous error