From 991d2ee282837a0ca3ec5a730e081274d37fa8b0 Mon Sep 17 00:00:00 2001
From: Rob Pilling <robpilling@gmail.com>
Date: Sat, 1 Feb 2020 19:21:54 +0000
Subject: [PATCH] Improve wording and docs for qualified path recovery

---
 src/librustc_parse/parser/path.rs                 | 15 +++++++++++----
 .../ui/parser/qualified-path-in-turbofish.fixed   |  2 +-
 src/test/ui/parser/qualified-path-in-turbofish.rs |  2 +-
 .../ui/parser/qualified-path-in-turbofish.stderr  |  2 +-
 4 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/librustc_parse/parser/path.rs b/src/librustc_parse/parser/path.rs
index 027380eaa2a6..5aa14c1739ff 100644
--- a/src/librustc_parse/parser/path.rs
+++ b/src/librustc_parse/parser/path.rs
@@ -81,17 +81,24 @@ impl<'a> Parser<'a> {
         Ok((qself, Path { segments: path.segments, span: lo.to(self.prev_span) }))
     }
 
+    /// Recover from an invalid single colon, when the user likely meant a qualified path.
+    ///
+    /// ```ignore (diagnostics)
+    /// <Bar as Baz<T>>:Qux
+    ///                ^ help: use double colon
+    /// ```
     fn recover_colon_before_qpath_proj(&mut self) -> bool {
         if self.token.kind != token::Colon {
             return false;
         }
 
-        // <Bar as Baz<T>>:Qux
-        //                ^
-        self.bump();
+        self.bump(); // colon
 
         self.diagnostic()
-            .struct_span_err(self.prev_span, "found single colon where type path was expected")
+            .struct_span_err(
+                self.prev_span,
+                "found single colon before projection in qualified path",
+            )
             .span_suggestion(
                 self.prev_span,
                 "use double colon",
diff --git a/src/test/ui/parser/qualified-path-in-turbofish.fixed b/src/test/ui/parser/qualified-path-in-turbofish.fixed
index a4213bdd3fb3..404d2f7762df 100644
--- a/src/test/ui/parser/qualified-path-in-turbofish.fixed
+++ b/src/test/ui/parser/qualified-path-in-turbofish.fixed
@@ -15,5 +15,5 @@ fn template<T>() -> i64 {
 
 fn main() {
     template::<<Impl as T>::Ty>();
-    //~^ ERROR found single colon where type path was expected
+    //~^ ERROR found single colon before projection in qualified path
 }
diff --git a/src/test/ui/parser/qualified-path-in-turbofish.rs b/src/test/ui/parser/qualified-path-in-turbofish.rs
index 75b2af2aa2e0..2f4b2ed348b9 100644
--- a/src/test/ui/parser/qualified-path-in-turbofish.rs
+++ b/src/test/ui/parser/qualified-path-in-turbofish.rs
@@ -15,5 +15,5 @@ fn template<T>() -> i64 {
 
 fn main() {
     template::<<Impl as T>:Ty>();
-    //~^ ERROR found single colon where type path was expected
+    //~^ ERROR found single colon before projection in qualified path
 }
diff --git a/src/test/ui/parser/qualified-path-in-turbofish.stderr b/src/test/ui/parser/qualified-path-in-turbofish.stderr
index 1fe6353b7a01..8857d2ef30cf 100644
--- a/src/test/ui/parser/qualified-path-in-turbofish.stderr
+++ b/src/test/ui/parser/qualified-path-in-turbofish.stderr
@@ -1,4 +1,4 @@
-error: found single colon where type path was expected
+error: found single colon before projection in qualified path
   --> $DIR/qualified-path-in-turbofish.rs:17:27
    |
 LL |     template::<<Impl as T>:Ty>();