Revert "pre-expansion gate associated_type_bounds"

This reverts commit c17a1fd.

Author: eddyb

src/libsyntax/feature_gate/check.rs

@@ -3,7 +3,10 @@ use super::accepted::ACCEPTED_FEATURES;
 use super::removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
 use super::builtin_attrs::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
 
-use crate::ast::{self, NodeId, GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
+use crate::ast::{
+    self, AssocTyConstraint, AssocTyConstraintKind, NodeId, GenericParam, GenericParamKind,
+    PatKind, RangeEnd, VariantData,
+};
 use crate::attr::{self, check_builtin_attribute};
 use crate::source_map::Spanned;
 use crate::edition::{ALL_EDITIONS, Edition};
@@ -604,6 +607,16 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_generic_param(self, param)
     }
 
+    fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
+        match constraint.kind {
+            AssocTyConstraintKind::Bound { .. } =>
+                gate_feature_post!(&self, associated_type_bounds, constraint.span,
+                    "associated type bounds are unstable"),
+            _ => {}
+        }
+        visit::walk_assoc_ty_constraint(self, constraint)
+    }
+
     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
         match ti.kind {
             ast::TraitItemKind::Method(ref sig, ref block) => {

src/test/ui/feature-gates/feature-gate-associated_type_bounds.rs

@@ -70,7 +70,3 @@ fn main() {
     // FIXME: uncomment when `impl_trait_in_bindings` feature is fixed.
     // let _: &dyn Tr1<As1: Copy> = &S1;
 }
-
-macro_rules! accept_path { ($p:path) => {} }
-accept_path!(Iterator<Item: Ord>);
-//~^ ERROR associated type bounds are unstable

src/test/ui/feature-gates/feature-gate-associated_type_bounds.stderr

@@ -115,15 +115,6 @@ LL |     let _: impl Tr1<As1: Copy> = S1;
    = note: for more information, see https://github.com/rust-lang/rust/issues/52662
    = help: add `#![feature(associated_type_bounds)]` to the crate attributes to enable
 
-error[E0658]: associated type bounds are unstable
-  --> $DIR/feature-gate-associated_type_bounds.rs:75:23
-   |
-LL | accept_path!(Iterator<Item: Ord>);
-   |                       ^^^^^^^^^
-   |
-   = note: for more information, see https://github.com/rust-lang/rust/issues/52662
-   = help: add `#![feature(associated_type_bounds)]` to the crate attributes to enable
-
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
   --> $DIR/feature-gate-associated_type_bounds.rs:54:14
    |
@@ -148,7 +139,7 @@ LL |     let _: impl Tr1<As1: Copy> = S1;
    |
    = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
 
-error: aborting due to 17 previous errors
+error: aborting due to 16 previous errors
 
 Some errors have detailed explanations: E0562, E0658.
 For more information about an error, try `rustc --explain E0562`.