Fix bad diagnostics for anon params with qualified paths

Author: JohnTitor

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1627,18 +1627,28 @@ impl<'a> Parser<'a> {
                 ),
                 // 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;
+                    match pat.clone().into_inner().kind {
+                        PatKind::Ident(_, ident, _) => {
+                            let mutab = mutab.prefix_str();
+                            (
+                                ident,
+                                format!("self: &{}{}", mutab, ident),
+                                format!("{}: &{}TypeName", ident, mutab),
+                                format!("_: &{}{}", mutab, ident),
+                            )
+                        }
+                        PatKind::Path(..) => {
+                            err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
+                            return None;
+                        }
+                        _ => return None,
                     }
                 }
+                // Also catches `fn foo(<Bar as T>::Baz)`
+                PatKind::Path(..) => {
+                    err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
+                    return None;
+                }
                 // Ignore other `PatKind`.
                 _ => return None,
             };

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

@@ -9,6 +9,12 @@ trait T {
     fn foo_with_ref(&mut i32);
     //~^ ERROR expected one of `:`, `@`, or `|`, found `)`
 
+    fn foo_with_qualified_path(<Bar as T>::Baz);
+    //~^ ERROR expected one of `(`, `...`, `..=`, `..`, `::`, `:`, `{`, or `|`, found `)`
+
+    fn foo_with_qualified_path_and_ref(&<Bar as T>::Baz);
+    //~^ 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

@@ -38,8 +38,24 @@ 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:12:47
+   |
+LL |     fn foo_with_qualified_path(<Bar as T>::Baz);
+   |                                               ^ expected one of 8 possible tokens
+   |
+   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
+
+error: expected one of `(`, `...`, `..=`, `..`, `::`, `:`, `{`, or `|`, found `)`
+  --> $DIR/anon-params-denied-2018.rs:15:56
+   |
+LL |     fn foo_with_qualified_path_and_ref(&<Bar as T>::Baz);
+   |                                                        ^ expected one of 8 possible tokens
+   |
+   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
+
 error: expected one of `:`, `@`, or `|`, found `,`
-  --> $DIR/anon-params-denied-2018.rs:12:36
+  --> $DIR/anon-params-denied-2018.rs:18:36
    |
 LL |     fn bar_with_default_impl(String, String) {}
    |                                    ^ expected one of `:`, `@`, or `|`
@@ -59,7 +75,7 @@ LL |     fn bar_with_default_impl(_: String, String) {}
    |                              ^^^^^^^^^
 
 error: expected one of `:`, `@`, or `|`, found `)`
-  --> $DIR/anon-params-denied-2018.rs:12:44
+  --> $DIR/anon-params-denied-2018.rs:18:44
    |
 LL |     fn bar_with_default_impl(String, String) {}
    |                                            ^ expected one of `:`, `@`, or `|`
@@ -75,7 +91,7 @@ LL |     fn bar_with_default_impl(String, _: String) {}
    |                                      ^^^^^^^^^
 
 error: expected one of `:`, `@`, or `|`, found `,`
-  --> $DIR/anon-params-denied-2018.rs:17:22
+  --> $DIR/anon-params-denied-2018.rs:23:22
    |
 LL |     fn baz(a:usize, b, c: usize) -> usize {
    |                      ^ expected one of `:`, `@`, or `|`
@@ -90,5 +106,5 @@ help: if this is a type, explicitly ignore the parameter name
 LL |     fn baz(a:usize, _: b, c: usize) -> usize {
    |                     ^^^^
 
-error: aborting due to 5 previous errors
+error: aborting due to 7 previous errors