parser: recover on `&'lifetime mut $pat`.

src/librustc_parse/parser/pat.rs

@@ -459,18 +459,28 @@ impl<'a> Parser<'a> {
     /// Parse `&pat` / `&mut pat`.
     fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
         self.expect_and()?;
+        self.recover_lifetime_in_deref_pat();
         let mutbl = self.parse_mutability();
-
-        if let token::Lifetime(name) = self.token.kind {
-            let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern", name));
-            err.span_label(self.token.span, "unexpected lifetime");
-            return Err(err);
-        }
-
         let subpat = self.parse_pat_with_range_pat(false, expected)?;
         Ok(PatKind::Ref(subpat, mutbl))
     }
 
+    fn recover_lifetime_in_deref_pat(&mut self) {
+        if let token::Lifetime(name) = self.token.kind {
+            self.bump(); // `'a`
+
+            let span = self.prev_span;
+            self.struct_span_err(span, &format!("unexpected lifetime `{}` in pattern", name))
+                .span_suggestion(
+                    span,
+                    "remove the lifetime",
+                    String::new(),
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+        }
+    }
+
     /// Parse a tuple or parenthesis pattern.
     fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
         let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;

src/test/ui/parser/lifetime-in-pattern-recover.rs

@@ -0,0 +1,6 @@
+fn main() {
+    let &'a x = &0; //~ ERROR unexpected lifetime `'a` in pattern
+    let &'a mut y = &mut 0; //~ ERROR unexpected lifetime `'a` in pattern
+
+    let _recovery_witness: () = 0; //~ ERROR mismatched types
+}

src/test/ui/parser/lifetime-in-pattern-recover.stderr

@@ -0,0 +1,23 @@
+error: unexpected lifetime `'a` in pattern
+  --> $DIR/lifetime-in-pattern-recover.rs:2:10
+   |
+LL |     let &'a x = &0;
+   |          ^^ help: remove the lifetime
+
+error: unexpected lifetime `'a` in pattern
+  --> $DIR/lifetime-in-pattern-recover.rs:3:10
+   |
+LL |     let &'a mut y = &mut 0;
+   |          ^^ help: remove the lifetime
+
+error[E0308]: mismatched types
+  --> $DIR/lifetime-in-pattern-recover.rs:5:33
+   |
+LL |     let _recovery_witness: () = 0;
+   |                            --   ^ expected `()`, found integer
+   |                            |
+   |                            expected due to this
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/parser/lifetime-in-pattern.rs

@@ -1,5 +1,6 @@
 fn test(&'a str) {
     //~^ ERROR unexpected lifetime `'a` in pattern
+    //~| ERROR expected one of `:`, `@`, or `|`, found `)`
 }
 
 fn main() {

src/test/ui/parser/lifetime-in-pattern.stderr

@@ -2,7 +2,13 @@ error: unexpected lifetime `'a` in pattern
   --> $DIR/lifetime-in-pattern.rs:1:10
    |
 LL | fn test(&'a str) {
-   |          ^^ unexpected lifetime
+   |          ^^ help: remove the lifetime
 
-error: aborting due to previous error
+error: expected one of `:`, `@`, or `|`, found `)`
+  --> $DIR/lifetime-in-pattern.rs:1:16
+   |
+LL | fn test(&'a str) {
+   |                ^ expected one of `:`, `@`, or `|`
+
+error: aborting due to 2 previous errors
 

src/test/ui/self/self-vs-path-ambiguity.stderr

@@ -2,7 +2,7 @@ error: unexpected lifetime `'a` in pattern
   --> $DIR/self-vs-path-ambiguity.rs:9:11
    |
 LL |     fn i(&'a self::S: &S) {}
-   |           ^^ unexpected lifetime
+   |           ^^ help: remove the lifetime
 
 error: aborting due to previous error