Add feature gate for Self and associated types in struct expressions and patterns

Author: petrochenkov

src/librustc_typeck/check/mod.rs

@@ -3235,6 +3235,16 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             }
             Def::Struct(..) | Def::Union(..) | Def::TyAlias(..) |
             Def::AssociatedTy(..) | Def::SelfTy(..) => {
+                match def {
+                    Def::AssociatedTy(..) | Def::SelfTy(..)
+                            if !self.tcx.sess.features.borrow().more_struct_aliases => {
+                        emit_feature_err(&self.tcx.sess.parse_sess,
+                                         "more_struct_aliases", path.span, GateIssue::Language,
+                                         "`Self` and associated types in struct \
+                                          expressions and patterns are unstable");
+                    }
+                    _ => {}
+                }
                 match ty.sty {
                     ty::TyAdt(adt, substs) if !adt.is_enum() => {
                         Some((adt.struct_variant(), adt.did, substs))

src/libsyntax/feature_gate.rs

@@ -309,6 +309,9 @@ declare_features! (
 
     // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
     (active, field_init_shorthand, "1.14.0", Some(37340)),
+
+    // Allows using `Self` and associated types in struct expressions and patterns.
+    (active, more_struct_aliases, "1.14.0", Some(37544)),
 );
 
 declare_features! (

src/test/compile-fail/struct-path-associated-type.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(more_struct_aliases)]
+
 struct S;
 
 trait Tr {

src/test/compile-fail/struct-path-self-feature-gate.rs

@@ -0,0 +1,29 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct S;
+
+trait Tr {
+    type A;
+}
+
+fn f<T: Tr<A = S>>() {
+    let _ = T::A {};
+    //~^ ERROR `Self` and associated types in struct expressions and patterns are unstable
+}
+
+impl S {
+    fn f() {
+        let _ = Self {};
+        //~^ ERROR `Self` and associated types in struct expressions and patterns are unstable
+    }
+}
+
+fn main() {}

src/test/compile-fail/struct-path-self-type-mismatch.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(more_struct_aliases)]
+
 struct Foo<A> { inner: A }
 
 trait Bar { fn bar(); }

src/test/compile-fail/struct-path-self.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(more_struct_aliases)]
+
 struct S;
 
 trait Tr {

src/test/run-pass/struct-path-associated-type.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(more_struct_aliases)]
+
 struct S<T, U = u16> {
     a: T,
     b: U,

src/test/run-pass/struct-path-self.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(more_struct_aliases)]
+
 use std::ops::Add;
 
 struct S<T, U = u16> {