From 5b58b1eae4c7c29a42fa2b506be2af9c26d9d200 Mon Sep 17 00:00:00 2001
From: topecongiro <seuchida@gmail.com>
Date: Sat, 21 Dec 2019 23:57:27 +0900
Subject: [PATCH 1/2] Use correct span

---
 src/matches.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/matches.rs b/src/matches.rs
index 83ece213ba8..60d93ac8c3e 100644
--- a/src/matches.rs
+++ b/src/matches.rs
@@ -45,6 +45,7 @@ impl<'a> ArmWrapper<'a> {
 impl<'a> Spanned for ArmWrapper<'a> {
     fn span(&self) -> Span {
         if let Some(lo) = self.beginning_vert {
+            let lo = std::cmp::min(lo, self.arm.span().lo());
             mk_sp(lo, self.arm.span().hi())
         } else {
             self.arm.span()

From 16fdb3954d3f0d0dc806b1b2932e2dafedb5e8bf Mon Sep 17 00:00:00 2001
From: topecongiro <seuchida@gmail.com>
Date: Sat, 21 Dec 2019 23:58:29 +0900
Subject: [PATCH 2/2] Add a test for #3974

---
 tests/target/issue-3974.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 tests/target/issue-3974.rs

diff --git a/tests/target/issue-3974.rs b/tests/target/issue-3974.rs
new file mode 100644
index 00000000000..a9f992ebd5c
--- /dev/null
+++ b/tests/target/issue-3974.rs
@@ -0,0 +1,10 @@
+fn emulate_foreign_item() {
+    match link_name {
+        // A comment here will duplicate the attribute
+        #[rustfmt::skip]
+        | "pthread_mutexattr_init"
+        | "pthread_mutexattr_settype"
+        | "pthread_mutex_init"
+        => {}
+    }
+}