Remove trailing whitespaces in macro def

src/comment.rs

@@ -505,6 +505,35 @@ pub fn contains_comment(text: &str) -> bool {
     CharClasses::new(text.chars()).any(|(kind, _)| kind.is_comment())
 }
 
+/// Remove trailing spaces from the specified snippet. We do not remove spaces
+/// inside strings or comments.
+pub fn remove_trailing_white_spaces(text: &str) -> String {
+    let mut buffer = String::with_capacity(text.len());
+    let mut space_buffer = String::with_capacity(128);
+    for (char_kind, c) in CharClasses::new(text.chars()) {
+        match c {
+            '\n' => {
+                if char_kind == FullCodeCharKind::InString {
+                    buffer.push_str(&space_buffer);
+                }
+                space_buffer.clear();
+                buffer.push('\n');
+            }
+            _ if c.is_whitespace() => {
+                space_buffer.push(c);
+            }
+            _ => {
+                if !space_buffer.is_empty() {
+                    buffer.push_str(&space_buffer);
+                    space_buffer.clear();
+                }
+                buffer.push(c);
+            }
+        }
+    }
+    buffer
+}
+
 struct CharClasses<T>
 where
     T: Iterator,

src/visitor.rs

@@ -18,8 +18,8 @@ use syntax::parse::ParseSess;
 
 use spanned::Spanned;
 use codemap::{LineRangeUtils, SpanUtils};
-use comment::{contains_comment, recover_missing_comment_in_span, CodeCharKind, CommentCodeSlices,
-              FindUncommented};
+use comment::{contains_comment, recover_missing_comment_in_span, remove_trailing_white_spaces,
+              CodeCharKind, CommentCodeSlices, FindUncommented};
 use comment::rewrite_comment;
 use config::{BraceStyle, Config};
 use items::{format_impl, format_struct, format_struct_struct, format_trait,
@@ -470,7 +470,7 @@ impl<'a> FmtVisitor<'a> {
             }
             ast::ItemKind::MacroDef(..) => {
                 // FIXME(#1539): macros 2.0
-                let mac_snippet = Some(self.snippet(item.span));
+                let mac_snippet = Some(remove_trailing_white_spaces(&self.snippet(item.span)));
                 self.push_rewrite(item.span, mac_snippet);
             }
         }