Fix https://github.com/nrc/rustfmt/issues/278

src/comment.rs

@@ -70,7 +70,11 @@ pub fn rewrite_comment(orig: &str, block_style: bool, width: usize, offset: usiz
             if line.len() > max_chars {
                 acc.push_str(&rewrite_string(line, &fmt));
             } else {
-                acc.push_str(line);
+                if line.len() == 0 {
+                    acc.pop(); // Remove space if this is an empty comment.
+                } else {
+                    acc.push_str(line);
+                }
             }
 
             (false, acc)

tests/source/struct_lits.rs

@@ -68,3 +68,18 @@ fn issue201() {
 fn issue201_2() {
     let s = S{a: S2{    .. c}, ..  b};
 }
+
+fn issue278() {
+    let s = S {
+        a: 0,
+        //       
+        b: 0,
+    };
+    let s1 = S {
+        a: 0,
+        // foo
+        //      
+        // bar
+        b: 0,
+    };
+}

tests/target/struct_lits.rs

@@ -86,3 +86,18 @@ fn issue201() {
 fn issue201_2() {
     let s = S { a: S2 { ..c }, ..b };
 }
+
+fn issue278() {
+    let s = S {
+        a: 0,
+        //
+        b: 0,
+    };
+    let s1 = S {
+        a: 0,
+        // foo
+        //
+        // bar
+        b: 0,
+    };
+}