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Fix panic when compiling Rocket.
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`Rustc::emit_diagnostic` reconstructs a diagnostic passed in from the
macro machinery. Currently it uses the type `DiagnosticBuilder<'_,
ErrorGuaranteed>`, which is incorrect, because the diagnostic might be a
warning. And if it is a warning, because of the `ErrorGuaranteed` we end
up calling into `emit_producing_error_guaranteed` and the assertion
within that function (correctly) fails because the level is not an error
level.

The fix is simple: change the type to `DiagnosticBuilder<'_, ()>`. Using
`()` works no matter what the diagnostic level is, and we don't need an
`ErrorGuaranteed` here.

The panic was reported in rust-lang#120576.
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nnethercote committed Feb 22, 2024
1 parent f8131a4 commit 326b44e
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion compiler/rustc_expand/src/proc_macro_server.rs
Original file line number Diff line number Diff line change
Expand Up @@ -510,7 +510,7 @@ impl server::FreeFunctions for Rustc<'_, '_> {

fn emit_diagnostic(&mut self, diagnostic: Diagnostic<Self::Span>) {
let message = rustc_errors::DiagnosticMessage::from(diagnostic.message);
let mut diag: DiagnosticBuilder<'_, rustc_errors::ErrorGuaranteed> =
let mut diag: DiagnosticBuilder<'_, ()> =
DiagnosticBuilder::new(&self.sess().dcx, diagnostic.level.to_internal(), message);
diag.span(MultiSpan::from_spans(diagnostic.spans));
for child in diagnostic.children {
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