Merge pull request rust-lang#3470 from topecongiro/issue-3051

Do not add a space after empty impl

Author: scampi

src/types.rs

@@ -667,9 +667,13 @@ impl Rewrite for ast::Ty {
                 rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
             }
             ast::TyKind::ImplicitSelf => Some(String::from("")),
-            ast::TyKind::ImplTrait(_, ref it) => it
-                .rewrite(context, shape)
-                .map(|it_str| format!("impl {}", it_str)),
+            ast::TyKind::ImplTrait(_, ref it) => {
+                // Empty trait is not a parser error.
+                it.rewrite(context, shape).map(|it_str| {
+                    let space = if it_str.is_empty() { "" } else { " " };
+                    format!("impl{}{}", space, it_str)
+                })
+            }
             ast::TyKind::CVarArgs => Some("...".to_owned()),
             ast::TyKind::Err | ast::TyKind::Typeof(..) => unreachable!(),
         }

tests/source/type.rs

@@ -83,6 +83,10 @@ impl Future<Item = (), Error = SomeError> + 'a,
     'c {
 }
 
+// #3051
+token![impl];
+token![ impl ];
+
 // #3060
 macro_rules! foo {
     ($foo_api: ty) => {

tests/target/type.rs

@@ -82,6 +82,10 @@ pub fn do_something<'a, T: Trait1 + Trait2 + 'a>(
 > + 'a + 'b + 'c {
 }
 
+// #3051
+token![impl];
+token![impl];
+
 // #3060
 macro_rules! foo {
     ($foo_api: ty) => {