fix 'extra comma inserted due to comment' (rust-lang#3677)

src/lists.rs

@@ -612,7 +612,11 @@ pub(crate) fn extract_post_comment(
         post_snippet[1..].trim_matches(white_space)
     } else if post_snippet.starts_with(separator) {
         post_snippet[separator.len()..].trim_matches(white_space)
-    } else if post_snippet.ends_with(',') && !post_snippet.trim().starts_with("//") {
+    }
+    // not comment or over two lines
+    else if post_snippet.ends_with(',')
+        && (!post_snippet.trim().starts_with("//") || post_snippet.trim().contains('\n'))
+    {
         post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space)
     } else {
         post_snippet

tests/source/issue-3675.rs

@@ -0,0 +1,5 @@
+ fn main() {
+    println!("{}"
+        // comment
+        , 111);
+ }

tests/target/issue-3675.rs

@@ -0,0 +1,6 @@
+fn main() {
+    println!(
+        "{}", // comment
+        111
+    );
+}