Auto merge of #49368 - matthewjasper:feature-gate-where-clause, r=<try>

Feature gate where clauses on associated types

Fixes #49365. Requires crater: these have been usable since 1.24.

Author: bors

src/libsyntax/feature_gate.rs

@@ -1723,8 +1723,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
             ast::TraitItemKind::Type(_, ref default) => {
-                // We use two if statements instead of something like match guards so that both
-                // of these errors can be emitted if both cases apply.
+                // We use three if statements instead of something like match guards so that all
+                // of these errors can be emitted if all cases apply.
                 if default.is_some() {
                     gate_feature_post!(&self, associated_type_defaults, ti.span,
                                        "associated type defaults are unstable");
@@ -1733,6 +1733,10 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     gate_feature_post!(&self, generic_associated_types, ti.span,
                                        "generic associated types are unstable");
                 }
+                if !ti.generics.where_clause.predicates.is_empty() {
+                    gate_feature_post!(&self, generic_associated_types, ti.span,
+                                       "where clauses on associated types are unstable");
+                }
             }
             _ => {}
         }

src/test/ui/feature-gate-generic_associated_types.rs

@@ -15,6 +15,7 @@ trait PointerFamily<U> {
     //~^ ERROR generic associated types are unstable
     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
     //~^ ERROR generic associated types are unstable
+    //~| ERROR where clauses on associated types are unstable
 }
 
 struct Foo;
@@ -25,4 +26,10 @@ impl PointerFamily<u32> for Foo {
     //~^ ERROR generic associated types are unstable
 }
 
+trait Bar {
+    type Assoc where Self: Sized;
+    //~^ ERROR where clauses on associated types are unstable
+}
+
+
 fn main() {}

src/test/ui/feature-gate-generic_associated_types.stderr

@@ -14,22 +14,38 @@ LL |     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
+error[E0658]: where clauses on associated types are unstable (see issue #44265)
+  --> $DIR/feature-gate-generic_associated_types.rs:16:5
+   |
+LL |     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(generic_associated_types)] to the crate attributes to enable
+
 error[E0658]: generic associated types are unstable (see issue #44265)
-  --> $DIR/feature-gate-generic_associated_types.rs:22:5
+  --> $DIR/feature-gate-generic_associated_types.rs:23:5
    |
 LL |     type Pointer<usize> = Box<usize>;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
 error[E0658]: generic associated types are unstable (see issue #44265)
-  --> $DIR/feature-gate-generic_associated_types.rs:24:5
+  --> $DIR/feature-gate-generic_associated_types.rs:25:5
    |
 LL |     type Pointer2<u32> = Box<u32>;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
-error: aborting due to 4 previous errors
+error[E0658]: where clauses on associated types are unstable (see issue #44265)
+  --> $DIR/feature-gate-generic_associated_types.rs:30:5
+   |
+LL |     type Assoc where Self: Sized;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(generic_associated_types)] to the crate attributes to enable
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0658`.