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Rollup merge of #112345 - bvanjoi:fix-112342, r=nilstrieb,est31
fix(expand): prevent infinity loop in macro containing only "///" Fixes #112342 Issue #112342 was caused by an infinity loop in `parse_tt_inner`, and the state of it is as follows: - `matcher`: `[Sequence, Token(Doc), SequenceKleeneOpNoSep(op: ZeroOrMore), Eof]` - loop: | Iteration | Action | | - | - | | 0 | enter `Sequence`| | 1 | enter `Token(Doc)` and `mp.idx += 1` had been executed | | 2 | enter `SequenceKleeneOpNoSep` and reset `mp.idx` to `1` | | 3 | enter `Token(Doc)` again| To prevent the infinite loop, a check for whether it only contains `DocComment` in `check_lhs_no_empty_seq` had been added.
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‎compiler/rustc_expand/src/mbe/macro_parser.rs

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@@ -249,6 +249,7 @@ pub(super) fn compute_locs(matcher: &[TokenTree]) -> Vec<MatcherLoc> {
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}
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/// A single matcher position, representing the state of matching.
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#[derive(Debug)]
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struct MatcherPos {
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/// The index into `TtParser::locs`, which represents the "dot".
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idx: usize,

‎compiler/rustc_expand/src/mbe/macro_rules.rs

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@@ -628,6 +628,40 @@ fn check_lhs_nt_follows(sess: &ParseSess, def: &ast::Item, lhs: &mbe::TokenTree)
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// after parsing/expansion. we can report every error in every macro this way.
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}
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fn is_empty_token_tree(sess: &ParseSess, seq: &mbe::SequenceRepetition) -> bool {
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if seq.separator.is_some() {
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false
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} else {
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let mut is_empty = true;
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let mut iter = seq.tts.iter().peekable();
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while let Some(tt) = iter.next() {
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match tt {
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mbe::TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)) => {}
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mbe::TokenTree::Token(t @ Token { kind: DocComment(..), .. }) => {
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let mut now = t;
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while let Some(&mbe::TokenTree::Token(
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next @ Token { kind: DocComment(..), .. },
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)) = iter.peek()
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{
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now = next;
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iter.next();
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}
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let span = t.span.to(now.span);
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sess.span_diagnostic.span_note_without_error(
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span,
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"doc comments are ignored in matcher position",
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);
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}
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mbe::TokenTree::Sequence(_, sub_seq)
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if (sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
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|| sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne) => {}
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_ => is_empty = false,
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}
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}
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is_empty
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}
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}
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/// Checks that the lhs contains no repetition which could match an empty token
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/// tree, because then the matcher would hang indefinitely.
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fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
@@ -644,16 +678,7 @@ fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
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}
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}
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TokenTree::Sequence(span, seq) => {
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if seq.separator.is_none()
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&& seq.tts.iter().all(|seq_tt| match seq_tt {
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TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)) => true,
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TokenTree::Sequence(_, sub_seq) => {
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sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
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|| sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
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}
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_ => false,
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})
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{
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if is_empty_token_tree(sess, seq) {
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let sp = span.entire();
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sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
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return false;

‎tests/ui/macros/issue-112342-1.rs

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@@ -0,0 +1,49 @@
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// same as #95267, ignore doc comment although it's a bug.
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macro_rules! m1 {
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(
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$(
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///
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)*
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//~^^^ERROR repetition matches empty token tree
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) => {};
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}
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m1! {}
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macro_rules! m2 {
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(
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$(
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///
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)+
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//~^^^ERROR repetition matches empty token tree
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) => {};
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}
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m2! {}
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macro_rules! m3 {
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(
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$(
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///
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)?
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//~^^^ERROR repetition matches empty token tree
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) => {};
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}
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m3! {}
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macro_rules! m4 {
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(
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$(
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///
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///
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)*
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//~^^^^ERROR repetition matches empty token tree
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) => {};
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}
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m4! {}
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fn main() {}

‎tests/ui/macros/issue-112342-1.stderr

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@@ -0,0 +1,64 @@
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-1.rs:6:13
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|
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LL | ///
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| ^^^
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error: repetition matches empty token tree
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--> $DIR/issue-112342-1.rs:5:10
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|
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LL | $(
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| __________^
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LL | | ///
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LL | | )*
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| |_________^
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-1.rs:17:13
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|
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LL | ///
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| ^^^
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error: repetition matches empty token tree
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--> $DIR/issue-112342-1.rs:16:10
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|
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LL | $(
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| __________^
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LL | | ///
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LL | | )+
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| |_________^
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-1.rs:28:13
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|
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LL | ///
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| ^^^
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error: repetition matches empty token tree
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--> $DIR/issue-112342-1.rs:27:10
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|
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LL | $(
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| __________^
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LL | | ///
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LL | | )?
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| |_________^
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-1.rs:40:13
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|
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LL | / ///
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LL | | ///
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| |_______________^
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error: repetition matches empty token tree
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--> $DIR/issue-112342-1.rs:39:10
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|
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LL | $(
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| __________^
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LL | | ///
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LL | | ///
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LL | | )*
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| |_________^
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error: aborting due to 4 previous errors
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‎tests/ui/macros/issue-112342-2.rs

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// check-pass
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// same as #95267, ignore doc comment although it's a bug.
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macro_rules! m1 {
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(
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$(
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///
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$expr: expr,
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)*
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) => {};
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}
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m1! {}
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macro_rules! m2 {
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(
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$(
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///
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$expr: expr,
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///
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)*
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) => {};
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}
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m2! {}
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macro_rules! m3 {
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(
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$(
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///
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$tt: tt,
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)*
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) => {};
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}
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m3! {}
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fn main() {}

‎tests/ui/macros/issue-112342-2.stderr

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@@ -0,0 +1,24 @@
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-2.rs:8:13
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|
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LL | ///
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| ^^^
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-2.rs:19:13
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|
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LL | ///
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| ^^^
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-2.rs:21:13
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|
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LL | ///
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| ^^^
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note: doc comments are ignored in matcher position
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--> $DIR/issue-112342-2.rs:31:13
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|
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LL | ///
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| ^^^
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