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Added help for eof message inside macro invocation #33963

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Added help for eof message inside macro invocation #33963

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7 changes: 7 additions & 0 deletions src/libsyntax/parse/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2440,6 +2440,13 @@ impl<'a> Parser<'a> {
err.cancel();
let msg = format!("expected expression, found {}",
self.this_token_descr());
if self.token == token::Token::Eof {
let help = format!("{} in this context refers \
to the end of the macro invocation",
self.this_token_descr());
return Err(self.span_fatal_help(
self.span, &msg, &help));
}
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@LeoTestard LeoTestard May 31, 2016 •
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You cannot know here that you are parsing the arguments of a macro invocation. I suspect that the following code:

static foo: u32 =

will trigger your error message. Which is obviously not what you want.

Besides, your code only handles the case where the macro parsing reaches EOF while trying to parse an expr. Thing is, macros can parse a lot of different fragments of Rust syntax and match arbitrary Rust tokens. So there are a lot of other places where you should handle this as well. As far as I know, it's not possible to handle them all because for those who use the Rust parser (like expr), you cannot know if you are parsing a macro invocation or not.

Maybe the easier solution would be to introduce a special token to indicate end of macro invocation that would behave like EOF except for error messages but that would be a lot of changes just to add an help message.

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Maybe the easier solution would be to introduce a special token to indicate end of macro invocation that would behave like EOF except for error messages but that would be a lot of changes just to add an help message.

This seems like a good idea to me, too.

return Err(self.fatal(&msg));
}
}
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16 changes: 16 additions & 0 deletions src/test/parse-fail/macro-eof-message.rs
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@@ -0,0 +1,16 @@
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


fn main() {
let message = "test";
println!("{}", message/); //~ ERROR expected expression, found `<eof>`
//~^ HELP `<eof>` in this context refers to the end of the macro invocation
}