fix ice in suggesting

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -405,7 +405,9 @@ impl<'a> Parser<'a> {
             let prev_span = self.prev_token.span.shrink_to_lo();
             let snapshot = self.create_snapshot_for_diagnostic();
             self.bump();
-            if self.parse_ty().is_ok() && self.token == token::Eq {
+            match self.parse_ty() {
+                Ok(_) => {
+                    if self.token == token::Eq {
                         err.span_suggestion_verbose(
                             prev_span,
                             "you might have meant to introduce a new binding",
@@ -413,6 +415,11 @@ impl<'a> Parser<'a> {
                             Applicability::MaybeIncorrect,
                         );
                     }
+                }
+                Err(err) => {
+                    err.cancel();
+                }
+            }
             self.restore_snapshot(snapshot);
         }
 

tests/ui/type/missing-let-in-binding-3.rs

@@ -0,0 +1,5 @@
+struct A {
+    : :u8, //~ ERROR expected identifier, found `:`
+}
+
+fn main() {}

tests/ui/type/missing-let-in-binding-3.stderr

@@ -0,0 +1,10 @@
+error: expected identifier, found `:`
+  --> $DIR/missing-let-in-binding-3.rs:2:5
+   |
+LL | struct A {
+   |        - while parsing this struct
+LL |     : :u8,
+   |     ^ expected identifier
+
+error: aborting due to previous error
+