From f3df63f8ee2102dbfacd664b38160e2d6ca4e5a7 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 29 Dec 2021 12:05:51 -0800
Subject: [PATCH 1/2] Add a pretty printer test of impl<T> const Trait

---
 src/test/ui/macros/stringify.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/test/ui/macros/stringify.rs b/src/test/ui/macros/stringify.rs
index 90bc7dc1da239..88305d22d7798 100644
--- a/src/test/ui/macros/stringify.rs
+++ b/src/test/ui/macros/stringify.rs
@@ -611,6 +611,12 @@ fn test_item() {
         ),
         "pub impl Trait for Struct {}",
     );
+    assert_eq!(
+        stringify_item!(
+            impl<T> const Trait for T {}
+        ),
+        "impl const <T> Trait for T {}", // FIXME
+    );
     assert_eq!(
         stringify_item!(
             impl ~const Struct {}

From a24e238bdf07b2e59f5d3af376647742a6d7f05a Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 29 Dec 2021 12:10:24 -0800
Subject: [PATCH 2/2] Fix spacing and ordering of words in pretty printed Impl

---
 compiler/rustc_ast_pretty/src/pprust/state.rs | 9 ++++++---
 src/test/ui/macros/stringify.rs               | 4 ++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index f0c1d017326cd..c2253e63356a4 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -1285,14 +1285,17 @@ impl<'a> State<'a> {
                 self.print_visibility(&item.vis);
                 self.print_defaultness(defaultness);
                 self.print_unsafety(unsafety);
-                self.word_nbsp("impl");
-                self.print_constness(constness);
+                self.word("impl");
 
-                if !generics.params.is_empty() {
+                if generics.params.is_empty() {
+                    self.nbsp();
+                } else {
                     self.print_generic_params(&generics.params);
                     self.space();
                 }
 
+                self.print_constness(constness);
+
                 if let ast::ImplPolarity::Negative(_) = polarity {
                     self.word("!");
                 }
diff --git a/src/test/ui/macros/stringify.rs b/src/test/ui/macros/stringify.rs
index 88305d22d7798..e2f47e0af54b2 100644
--- a/src/test/ui/macros/stringify.rs
+++ b/src/test/ui/macros/stringify.rs
@@ -603,7 +603,7 @@ fn test_item() {
         stringify_item!(
             impl<T> Struct<T> {}
         ),
-        "impl <T> Struct<T> {}", // FIXME
+        "impl<T> Struct<T> {}",
     );
     assert_eq!(
         stringify_item!(
@@ -615,7 +615,7 @@ fn test_item() {
         stringify_item!(
             impl<T> const Trait for T {}
         ),
-        "impl const <T> Trait for T {}", // FIXME
+        "impl<T> const Trait for T {}",
     );
     assert_eq!(
         stringify_item!(