diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index 77ec598e62a..460a06f9c06 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -12,7 +12,7 @@ use rustc_ast::{self as ast, DUMMY_NODE_ID, NodeId};
use rustc_ast_pretty::pprust;
use rustc_attr_parsing::{AttributeKind, find_attr};
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
-use rustc_errors::{Applicability, ErrorGuaranteed};
+use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
use rustc_feature::Features;
use rustc_hir as hir;
use rustc_lint_defs::BuiltinLintDiag;
@@ -27,19 +27,18 @@ use rustc_span::hygiene::Transparency;
use rustc_span::{Ident, MacroRulesNormalizedIdent, Span, kw, sym};
use tracing::{debug, instrument, trace, trace_span};
-use super::diagnostics;
use super::macro_parser::{NamedMatches, NamedParseResult};
+use super::{SequenceRepetition, diagnostics};
use crate::base::{
DummyResult, ExpandResult, ExtCtxt, MacResult, MacroExpanderResult, SyntaxExtension,
SyntaxExtensionKind, TTMacroExpander,
};
use crate::expand::{AstFragment, AstFragmentKind, ensure_complete_parse, parse_ast_fragment};
-use crate::mbe;
use crate::mbe::diagnostics::{annotate_doc_comment, parse_failure_msg};
-use crate::mbe::macro_check;
use crate::mbe::macro_parser::NamedMatch::*;
use crate::mbe::macro_parser::{Error, ErrorReported, Failure, MatcherLoc, Success, TtParser};
use crate::mbe::transcribe::transcribe;
+use crate::mbe::{self, KleeneOp, macro_check};
pub(crate) struct ParserAnyMacro<'a> {
parser: Parser<'a>,
@@ -640,6 +639,37 @@ fn is_empty_token_tree(sess: &Session, seq: &mbe::SequenceRepetition) -> bool {
}
}
+/// Checks if a `vis` nonterminal fragment is unnecessarily wrapped in an optional repetition.
+///
+/// When a `vis` fragment (which can already be empty) is wrapped in `$(...)?`,
+/// this suggests removing the redundant repetition syntax since it provides no additional benefit.
+fn check_redundant_vis_repetition(
+ err: &mut Diag<'_>,
+ sess: &Session,
+ seq: &SequenceRepetition,
+ span: &DelimSpan,
+) {
+ let is_zero_or_one: bool = seq.kleene.op == KleeneOp::ZeroOrOne;
+ let is_vis = seq.tts.first().map_or(false, |tt| {
+ matches!(tt, mbe::TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)))
+ });
+
+ if is_vis && is_zero_or_one {
+ err.note("a `vis` fragment can already be empty");
+ err.multipart_suggestion(
+ "remove the `$(` and `)?`",
+ vec![
+ (
+ sess.source_map().span_extend_to_prev_char_before(span.open, '$', true),
+ "".to_string(),
+ ),
+ (span.close.with_hi(seq.kleene.span.hi()), "".to_string()),
+ ],
+ Applicability::MaybeIncorrect,
+ );
+ }
+}
+
/// Checks that the lhs contains no repetition which could match an empty token
/// tree, because then the matcher would hang indefinitely.
fn check_lhs_no_empty_seq(sess: &Session, tts: &[mbe::TokenTree]) -> Result<(), ErrorGuaranteed> {
@@ -654,8 +684,10 @@ fn check_lhs_no_empty_seq(sess: &Session, tts: &[mbe::TokenTree]) -> Result<(),
TokenTree::Sequence(span, seq) => {
if is_empty_token_tree(sess, seq) {
let sp = span.entire();
- let guar = sess.dcx().span_err(sp, "repetition matches empty token tree");
- return Err(guar);
+ let mut err =
+ sess.dcx().struct_span_err(sp, "repetition matches empty token tree");
+ check_redundant_vis_repetition(&mut err, sess, seq, span);
+ return Err(err.emit());
}
check_lhs_no_empty_seq(sess, &seq.tts)?
}
diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index 6fdf8e46fec..0273bb040f4 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -633,6 +633,24 @@ impl SourceMap {
sp
}
+ /// Extends the given `Span` to just before the previous occurrence of `c`. Return the same span
+ /// if an error occurred while retrieving the code snippet.
+ pub fn span_extend_to_prev_char_before(
+ &self,
+ sp: Span,
+ c: char,
+ accept_newlines: bool,
+ ) -> Span {
+ if let Ok(prev_source) = self.span_to_prev_source(sp) {
+ let prev_source = prev_source.rsplit(c).next().unwrap_or("");
+ if accept_newlines || !prev_source.contains('\n') {
+ return sp.with_lo(BytePos(sp.lo().0 - prev_source.len() as u32 - 1_u32));
+ }
+ }
+
+ sp
+ }
+
/// Extends the given `Span` to just after the previous occurrence of `pat` when surrounded by
/// whitespace. Returns None if the pattern could not be found or if an error occurred while
/// retrieving the code snippet.
diff --git a/tests/ui/macros/remove-repetition-issue-139480.rs b/tests/ui/macros/remove-repetition-issue-139480.rs
new file mode 100644
index 00000000000..1efb4306763
--- /dev/null
+++ b/tests/ui/macros/remove-repetition-issue-139480.rs
@@ -0,0 +1,28 @@
+macro_rules! ciallo {
+ ($($v: vis)? $name: ident) => {
+ //~^ error: repetition matches empty token tree
+ };
+}
+
+macro_rules! meow {
+ ($name: ident $($v: vis)?) => {
+ //~^ error: repetition matches empty token tree
+ };
+}
+
+macro_rules! gbc {
+ ($name: ident $/*
+ this comment gets removed by the suggestion
+ */
+ ($v: vis)?) => {
+ //~^ error: repetition matches empty token tree
+ };
+}
+
+ciallo!(hello);
+
+meow!(miaow, pub);
+
+gbc!(mygo,);
+
+fn main() {}
diff --git a/tests/ui/macros/remove-repetition-issue-139480.stderr b/tests/ui/macros/remove-repetition-issue-139480.stderr
new file mode 100644
index 00000000000..c2475589ee9
--- /dev/null
+++ b/tests/ui/macros/remove-repetition-issue-139480.stderr
@@ -0,0 +1,44 @@
+error: repetition matches empty token tree
+ --> $DIR/remove-repetition-issue-139480.rs:2:7
+ |
+LL | ($($v: vis)? $name: ident) => {
+ | ^^^^^^^^^
+ |
+ = note: a `vis` fragment can already be empty
+help: remove the `$(` and `)?`
+ |
+LL - ($($v: vis)? $name: ident) => {
+LL + ($v: vis $name: ident) => {
+ |
+
+error: repetition matches empty token tree
+ --> $DIR/remove-repetition-issue-139480.rs:8:20
+ |
+LL | ($name: ident $($v: vis)?) => {
+ | ^^^^^^^^^
+ |
+ = note: a `vis` fragment can already be empty
+help: remove the `$(` and `)?`
+ |
+LL - ($name: ident $($v: vis)?) => {
+LL + ($name: ident $v: vis) => {
+ |
+
+error: repetition matches empty token tree
+ --> $DIR/remove-repetition-issue-139480.rs:17:9
+ |
+LL | ($v: vis)?) => {
+ | ^^^^^^^^^
+ |
+ = note: a `vis` fragment can already be empty
+help: remove the `$(` and `)?`
+ |
+LL - ($name: ident $/*
+LL - this comment gets removed by the suggestion
+LL - */
+LL - ($v: vis)?) => {
+LL + ($name: ident $v: vis) => {
+ |
+
+error: aborting due to 3 previous errors
+