Fix bad diagnostics for anon params with ref

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1613,18 +1613,42 @@ impl<'a> Parser<'a> {
                 Applicability::HasPlaceholders,
             );
             return Some(ident);
-        } else if let PatKind::Ident(_, ident, _) = pat.kind {
+        } else if require_name
-            if require_name
             && (self.token == token::Comma
                 || self.token == token::Lt
                 || self.token == token::CloseDelim(token::Paren))
         {
+            let (ident, self_sugg, param_sugg, type_sugg) = match pat.kind {
+                PatKind::Ident(_, ident, _) => (
+                    ident,
+                    format!("self: {}", ident),
+                    format!("{}: TypeName", ident),
+                    format!("_: {}", ident),
+                ),
+                // Also catches `fn foo(&a)`.
+                PatKind::Ref(ref pat, mutab) => {
+                    if let PatKind::Ident(_, ident, _) = pat.clone().into_inner().kind {
+                        let mutab = mutab.prefix_str();
+                        (
+                            ident,
+                            format!("self: &{}{}", mutab, ident),
+                            format!("{}: &{}TypeName", ident, mutab),
+                            format!("_: &{}{}", mutab, ident),
+                        )
+                    } else {
+                        return None;
+                    }
+                }
+                // Ignore other `PatKind`.
+                _ => return None,
+            };
+
             // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
             if first_param {
                 err.span_suggestion(
                     pat.span,
                     "if this is a `self` type, give it a parameter name",
-                        format!("self: {}", ident),
+                    self_sugg,
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -1634,14 +1658,14 @@ impl<'a> Parser<'a> {
                 err.span_suggestion(
                     pat.span,
                     "if this is a parameter name, give it a type",
-                        format!("{}: TypeName", ident),
+                    param_sugg,
                     Applicability::HasPlaceholders,
                 );
             }
             err.span_suggestion(
                 pat.span,
                 "if this is a type, explicitly ignore the parameter name",
-                    format!("_: {}", ident),
+                type_sugg,
                 Applicability::MachineApplicable,
             );
             err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
@@ -1649,7 +1673,6 @@ impl<'a> Parser<'a> {
             // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
             return if self.token == token::Lt { None } else { Some(ident) };
         }
-        }
         None
     }
 

src/test/ui/anon-params/anon-params-denied-2018.rs

@@ -5,6 +5,10 @@
 trait T {
     fn foo(i32); //~ expected one of `:`, `@`, or `|`, found `)`
 
+    // Also checks with `&`
+    fn foo_with_ref(&mut i32);
+    //~^ ERROR expected one of `:`, `@`, or `|`, found `)`
+
     fn bar_with_default_impl(String, String) {}
     //~^ ERROR expected one of `:`
     //~| ERROR expected one of `:`

src/test/ui/anon-params/anon-params-denied-2018.stderr

@@ -18,8 +18,28 @@ help: if this is a type, explicitly ignore the parameter name
 LL |     fn foo(_: i32);
    |            ^^^^^^
 
+error: expected one of `:`, `@`, or `|`, found `)`
+  --> $DIR/anon-params-denied-2018.rs:9:29
+   |
+LL |     fn foo_with_ref(&mut i32);
+   |                             ^ expected one of `:`, `@`, or `|`
+   |
+   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
+help: if this is a `self` type, give it a parameter name
+   |
+LL |     fn foo_with_ref(self: &mut i32);
+   |                     ^^^^^^^^^^^^^^
+help: if this is a parameter name, give it a type
+   |
+LL |     fn foo_with_ref(i32: &mut TypeName);
+   |                     ^^^^^^^^^^^^^^^^^^
+help: if this is a type, explicitly ignore the parameter name
+   |
+LL |     fn foo_with_ref(_: &mut i32);
+   |                     ^^^^^^^^^^^
+
 error: expected one of `:`, `@`, or `|`, found `,`
-  --> $DIR/anon-params-denied-2018.rs:8:36
+  --> $DIR/anon-params-denied-2018.rs:12:36
    |
 LL |     fn bar_with_default_impl(String, String) {}
    |                                    ^ expected one of `:`, `@`, or `|`
@@ -39,7 +59,7 @@ LL |     fn bar_with_default_impl(_: String, String) {}
    |                              ^^^^^^^^^
 
 error: expected one of `:`, `@`, or `|`, found `)`
-  --> $DIR/anon-params-denied-2018.rs:8:44
+  --> $DIR/anon-params-denied-2018.rs:12:44
    |
 LL |     fn bar_with_default_impl(String, String) {}
    |                                            ^ expected one of `:`, `@`, or `|`
@@ -55,7 +75,7 @@ LL |     fn bar_with_default_impl(String, _: String) {}
    |                                      ^^^^^^^^^
 
 error: expected one of `:`, `@`, or `|`, found `,`
-  --> $DIR/anon-params-denied-2018.rs:13:22
+  --> $DIR/anon-params-denied-2018.rs:17:22
    |
 LL |     fn baz(a:usize, b, c: usize) -> usize {
    |                      ^ expected one of `:`, `@`, or `|`
@@ -70,5 +90,5 @@ help: if this is a type, explicitly ignore the parameter name
 LL |     fn baz(a:usize, _: b, c: usize) -> usize {
    |                     ^^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 

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

@@ -9,6 +9,20 @@ error: expected one of `:`, `@`, or `|`, found `)`
    |
 LL | fn test(&'a str) {
    |                ^ expected one of `:`, `@`, or `|`
+   |
+   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
+help: if this is a `self` type, give it a parameter name
+   |
+LL | fn test(self: &str) {
+   |         ^^^^^^^^^^
+help: if this is a parameter name, give it a type
+   |
+LL | fn test(str: &TypeName) {
+   |         ^^^^^^^^^^^^^^
+help: if this is a type, explicitly ignore the parameter name
+   |
+LL | fn test(_: &str) {
+   |         ^^^^^^^
 
 error: aborting due to 2 previous errors