From c927743b7b7bd382836dcce2d1140a7e829dc3d0 Mon Sep 17 00:00:00 2001
From: bohan <bohan-zhang@foxmail.com>
Date: Tue, 6 Jun 2023 23:11:08 +0800
Subject: [PATCH] fix(expand): prevent infinity loop in macro containing only
 "///"

---
 compiler/rustc_expand/src/mbe/macro_parser.rs |  1 +
 compiler/rustc_expand/src/mbe/macro_rules.rs  |  1 +
 tests/ui/macros/issue-112342-1.rs             | 36 +++++++++++++++++++
 tests/ui/macros/issue-112342-1.stderr         | 29 +++++++++++++++
 tests/ui/macros/issue-112342-2.rs             | 28 +++++++++++++++
 5 files changed, 95 insertions(+)
 create mode 100644 tests/ui/macros/issue-112342-1.rs
 create mode 100644 tests/ui/macros/issue-112342-1.stderr
 create mode 100644 tests/ui/macros/issue-112342-2.rs

diff --git a/compiler/rustc_expand/src/mbe/macro_parser.rs b/compiler/rustc_expand/src/mbe/macro_parser.rs
index 1c222fb4a89..f0e67cfd50e 100644
--- a/compiler/rustc_expand/src/mbe/macro_parser.rs
+++ b/compiler/rustc_expand/src/mbe/macro_parser.rs
@@ -249,6 +249,7 @@ pub(super) fn compute_locs(matcher: &[TokenTree]) -> Vec<MatcherLoc> {
 }
 
 /// A single matcher position, representing the state of matching.
+#[derive(Debug)]
 struct MatcherPos {
     /// The index into `TtParser::locs`, which represents the "dot".
     idx: usize,
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index e4c65a2049b..576d636d489 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -647,6 +647,7 @@ fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
                 if seq.separator.is_none()
                     && seq.tts.iter().all(|seq_tt| match seq_tt {
                         TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)) => true,
+                        TokenTree::Token(t) => matches!(t, Token { kind: DocComment(..), .. }),
                         TokenTree::Sequence(_, sub_seq) => {
                             sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
                                 || sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
diff --git a/tests/ui/macros/issue-112342-1.rs b/tests/ui/macros/issue-112342-1.rs
new file mode 100644
index 00000000000..14fe9bbd97a
--- /dev/null
+++ b/tests/ui/macros/issue-112342-1.rs
@@ -0,0 +1,36 @@
+// same as #95267, ignore doc comment although it's a bug.
+
+macro_rules! m1 {
+    (
+        $(
+            ///
+        )*
+        //~^^^ERROR repetition matches empty token tree
+    ) => {};
+}
+
+m1! {}
+
+macro_rules! m2 {
+    (
+        $(
+            ///
+        )+
+        //~^^^ERROR repetition matches empty token tree
+    ) => {};
+}
+
+m2! {}
+
+macro_rules! m3 {
+    (
+        $(
+            ///
+        )?
+        //~^^^ERROR repetition matches empty token tree
+    ) => {};
+}
+
+m3! {}
+
+fn main() {}
diff --git a/tests/ui/macros/issue-112342-1.stderr b/tests/ui/macros/issue-112342-1.stderr
new file mode 100644
index 00000000000..1ba7c0ffd3b
--- /dev/null
+++ b/tests/ui/macros/issue-112342-1.stderr
@@ -0,0 +1,29 @@
+error: repetition matches empty token tree
+  --> $DIR/issue-112342-1.rs:5:10
+   |
+LL |           $(
+   |  __________^
+LL | |             ///
+LL | |         )*
+   | |_________^
+
+error: repetition matches empty token tree
+  --> $DIR/issue-112342-1.rs:16:10
+   |
+LL |           $(
+   |  __________^
+LL | |             ///
+LL | |         )+
+   | |_________^
+
+error: repetition matches empty token tree
+  --> $DIR/issue-112342-1.rs:27:10
+   |
+LL |           $(
+   |  __________^
+LL | |             ///
+LL | |         )?
+   | |_________^
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui/macros/issue-112342-2.rs b/tests/ui/macros/issue-112342-2.rs
new file mode 100644
index 00000000000..1e1d953fa52
--- /dev/null
+++ b/tests/ui/macros/issue-112342-2.rs
@@ -0,0 +1,28 @@
+// check-pass
+
+// same as #95267, ignore doc comment although it's a bug.
+
+macro_rules! m1 {
+    (
+        $(
+            ///
+            $expr: expr,
+        )*
+    ) => {};
+}
+
+m1! {}
+
+macro_rules! m2 {
+    (
+        $(
+            ///
+            $expr: expr,
+            ///
+        )*
+    ) => {};
+}
+
+m2! {}
+
+fn main() {}