Make diff conflict marker error higher priority than unclosed delimeter

[joshka]

I tried this code:

mod tests {
    #[test]
<<<<<<< HEAD
    fn test1() {
=======
    fn test2() {
>>>>>>> 7a4f13c blah blah blah
    }
}

I expected to see this happen: explanation
error: encountered diff marker

Instead, this happened: explanation
error: this file contains an unclosed delimiter

Meta

rustc --version --verbose:

rustc 1.72.1 (d5c2e9c34 2023-09-13)
binary: rustc
commit-hash: d5c2e9c342b358556da91d61ed4133f6f50fc0c3
commit-date: 2023-09-13
host: aarch64-apple-darwin
release: 1.72.1
LLVM version: 16.0.5

[Rageking8]

@rustbot label +T-compiler +A-diagnostics

[fmease]

Right, this is happens because the unclosed delimiter error is emitted in the lexer (rustc_parse::lexer not rustc_lexer) before the parser (which is responsible for detecting diff markers) gets the chance to parse anything.

[joshka]

Right, this is happens because the unclosed delimiter error is emitted in the lexer (rustc_parse::lexer not rustc_lexer) before the parser (which is responsible for detecting diff markers) gets the chance to parse anything.

Reading between the line that sounds like it fits in the difficult to implement with only a small amount of value basket. Does this sound right?

[workingjubilee]

correct, you would have to be able to traverse the previous diagnostic errors already to-be-emitted and then swallow the previous one, I think. I don't know if our diagnostic architecture even allows that?

[estebank]

We have done similar things by storing some related unemitted DiagnosticBuilders and ferry them around from one stage to the next and only emit them try to find them later through some key (like a Span) and if present we remove it/delay_as_bug, but this is very ad-hoc at the moment.