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Improve the error message when forwarding a matched fragment to another macro #110222

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Merged
bors merged 2 commits into from
Apr 12, 2023
Merged

Improve the error message when forwarding a matched fragment to another macro #110222

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4b456cb
compiler: improve captured metavariables diagnostic
lovelymono Apr 12, 2023
04f20d4
compiler: print the suggestion only for local macros
lovelymono Apr 12, 2023
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7 changes: 6 additions & 1 deletion compiler/rustc_expand/src/mbe/diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -66,7 +66,12 @@ pub(super) fn failed_to_match_macro<'cx>(
&& (matches!(expected_token.kind, TokenKind::Interpolated(_))
|| matches!(token.kind, TokenKind::Interpolated(_)))
{
err.note("captured metavariables except for `$tt`, `$ident` and `$lifetime` cannot be compared to other tokens");
err.note("captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens");
err.note("see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information");

if !def_span.is_dummy() && !cx.source_map().is_imported(def_span) {
err.help("try using `:tt` instead in the macro definition");
}
}

// Check whether there's a missing comma in this macro call, like `println!("{}" a);`
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4 changes: 3 additions & 1 deletion tests/ui/macros/nonterminal-matching.stderr
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Expand Up @@ -18,7 +18,9 @@ LL | macro n(a $nt_item b) {
...
LL | complex_nonterminal!(enum E {});
| ------------------------------- in this macro invocation
= note: captured metavariables except for `$tt`, `$ident` and `$lifetime` cannot be compared to other tokens
= note: captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens
= note: see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information
= help: try using `:tt` instead in the macro definition
= note: this error originates in the macro `complex_nonterminal` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error
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