pre-expansion gate associated_type_bounds

src/libsyntax/feature_gate/check.rs

@@ -3,10 +3,7 @@ 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, AssocTyConstraint, AssocTyConstraintKind, NodeId, GenericParam, GenericParamKind,
-    PatKind, RangeEnd, VariantData,
-};
+use crate::ast::{self, NodeId, GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
 use crate::attr::{self, check_builtin_attribute};
 use crate::source_map::Spanned;
 use crate::edition::{ALL_EDITIONS, Edition};
@@ -584,16 +581,6 @@ 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) => {
@@ -859,6 +846,7 @@ pub fn check_crate(krate: &ast::Crate,
     gate_all!(or_patterns, "or-patterns syntax is experimental");
     gate_all!(const_extern_fn, "`const extern fn` definitions are unstable");
     gate_all!(trait_alias, "trait aliases are experimental");
+    gate_all!(associated_type_bounds, "associated type bounds are unstable");
 
     visit::walk_crate(&mut visitor, krate);
 }

src/libsyntax/parse/parser/path.rs

@@ -404,8 +404,9 @@ impl<'a> Parser<'a> {
                 // Parse lifetime argument.
                 args.push(GenericArg::Lifetime(self.expect_lifetime()));
                 misplaced_assoc_ty_constraints.append(&mut assoc_ty_constraints);
-            } else if self.check_ident() && self.look_ahead(1,
-                    |t| t == &token::Eq || t == &token::Colon) {
+            } else if self.check_ident()
+                && self.look_ahead(1, |t| t == &token::Eq || t == &token::Colon)
+            {
                 // Parse associated type constraint.
                 let lo = self.token.span;
                 let ident = self.parse_ident()?;
@@ -420,7 +421,14 @@ impl<'a> Parser<'a> {
                 } else {
                     unreachable!();
                 };
+
                 let span = lo.to(self.prev_span);
+
+                // Gate associated type bounds, e.g., `Iterator<Item: Ord>`.
+                if let AssocTyConstraintKind::Bound { .. } = kind {
+                    self.sess.gated_spans.associated_type_bounds.borrow_mut().push(span);
+                }
+
                 constraints.push(AssocTyConstraint {
                     id: ast::DUMMY_NODE_ID,
                     ident,

src/libsyntax/sess.rs

@@ -32,6 +32,8 @@ crate struct GatedSpans {
     crate const_extern_fn: Lock<Vec<Span>>,
     /// Spans collected for gating `trait_alias`, e.g. `trait Foo = Ord + Eq;`.
     pub trait_alias: Lock<Vec<Span>>,
+    /// Spans collected for gating `associated_type_bounds`, e.g. `Iterator<Item: Ord>`.
+    pub associated_type_bounds: Lock<Vec<Span>>,
 }
 
 /// Info about a parsing session.

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

@@ -70,3 +70,7 @@ 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

@@ -115,6 +115,15 @@ 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
    |
@@ -139,7 +148,7 @@ LL |     let _: impl Tr1<As1: Copy> = S1;
    |
    = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
 
-error: aborting due to 16 previous errors
+error: aborting due to 17 previous errors
 
 Some errors have detailed explanations: E0562, E0658.
 For more information about an error, try `rustc --explain E0562`.