diff --git a/compiler/rustc_expand/src/mbe/diagnostics.rs b/compiler/rustc_expand/src/mbe/diagnostics.rs index f469b2daef5..b1d9cea2773 100644 --- a/compiler/rustc_expand/src/mbe/diagnostics.rs +++ b/compiler/rustc_expand/src/mbe/diagnostics.rs @@ -1,12 +1,10 @@ -use std::borrow::Cow; - use crate::base::{DummyResult, ExtCtxt, MacResult}; use crate::expand::{parse_ast_fragment, AstFragmentKind}; use crate::mbe::{ macro_parser::{MatcherLoc, NamedParseResult, ParseResult::*, TtParser}, macro_rules::{try_match_macro, Tracker}, }; -use rustc_ast::token::{self, Token}; +use rustc_ast::token::{self, Token, TokenKind}; use rustc_ast::tokenstream::TokenStream; use rustc_ast_pretty::pprust; use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, DiagnosticMessage}; @@ -14,6 +12,7 @@ use rustc_parse::parser::{Parser, Recovery}; use rustc_span::source_map::SourceMap; use rustc_span::symbol::Ident; use rustc_span::Span; +use std::borrow::Cow; use super::macro_rules::{parser_from_cx, NoopTracker}; @@ -63,6 +62,13 @@ pub(super) fn failed_to_match_macro<'cx>( err.note(format!("while trying to match {remaining_matcher}")); } + if let MatcherLoc::Token { token: expected_token } = &remaining_matcher + && (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"); + } + // Check whether there's a missing comma in this macro call, like `println!("{}" a);` if let Some((arg, comma_span)) = arg.add_comma() { for lhs in lhses { diff --git a/tests/ui/macros/nonterminal-matching.stderr b/tests/ui/macros/nonterminal-matching.stderr index 5bbd5439098..762ecc3207f 100644 --- a/tests/ui/macros/nonterminal-matching.stderr +++ b/tests/ui/macros/nonterminal-matching.stderr @@ -18,6 +18,7 @@ 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: 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