Suggest let for possible binding with ty

2 files changed, 17 insertions, 9 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 36883bd2172..e8f47346fa7 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -399,6 +399,23 @@ impl<'a> Parser<'a> {
                 }
             }
         }
+        // we suggest add the missing `let` before the identifier
+        // `a: Ty = 1` -> `let a: Ty = 1`
+        if self.token == token::Colon {
+            let prev_span = self.prev_token.span.shrink_to_lo();
+            let snapshot = self.create_snapshot_for_diagnostic();
+            self.bump();
+            let res = self.parse_ty();
+            if res.is_ok() && self.token == token::Eq {
+                err.span_suggestion_verbose(
+                    prev_span,
+                    "you might have meant to introduce a new binding",
+                    "let ".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            self.restore_snapshot(snapshot);
+        }
 
         if let Some(recovered_ident) = recovered_ident && recover {
             err.emit();
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 1c17de337e8..ab04219b177 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -555,7 +555,6 @@ impl<'a> Parser<'a> {
                     if self.token == token::Colon {
                         // if next token is following a colon, it's likely a path
                         // and we can suggest a path separator
-                        let ident_span = self.prev_token.span;
                         self.bump();
                         if self.token.span.lo() == self.prev_token.span.hi() {
                             err.span_suggestion_verbose(
@@ -565,14 +564,6 @@ impl<'a> Parser<'a> {
                                 Applicability::MaybeIncorrect,
                             );
                         }
-                        if self.look_ahead(1, |token| token == &token::Eq) {
-                            err.span_suggestion_verbose(
-                                ident_span.shrink_to_lo(),
-                                "you might have meant to introduce a new binding",
-                                "let ",
-                                Applicability::MaybeIncorrect,
-                            );
-                        }
                         if self.sess.unstable_features.is_nightly_build() {
                             // FIXME(Nilstrieb): Remove this again after a few months.
                             err.note("type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>");