From 50ecee241008a17a3d296f0a0d2a4ff9080a5c57 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Thu, 15 Sep 2016 00:51:46 +0300
Subject: [PATCH] Add feature gate for Self and associated types in struct
 expressions and patterns

---
 src/librustc_typeck/check/mod.rs              | 10 +++++++
 src/libsyntax/feature_gate.rs                 |  3 ++
 .../struct-path-associated-type.rs            |  2 ++
 .../struct-path-self-feature-gate.rs          | 29 +++++++++++++++++++
 .../struct-path-self-type-mismatch.rs         |  2 ++
 src/test/compile-fail/struct-path-self.rs     |  2 ++
 .../run-pass/struct-path-associated-type.rs   |  2 ++
 src/test/run-pass/struct-path-self.rs         |  2 ++
 8 files changed, 52 insertions(+)
 create mode 100644 src/test/compile-fail/struct-path-self-feature-gate.rs

diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 75a14bb3db9..9a40cbb824a 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/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))
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 129e4a82338..69dfe8e8620 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/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! (
diff --git a/src/test/compile-fail/struct-path-associated-type.rs b/src/test/compile-fail/struct-path-associated-type.rs
index 660ac44ce0b..ecaf269fcb1 100644
--- a/src/test/compile-fail/struct-path-associated-type.rs
+++ b/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 {
diff --git a/src/test/compile-fail/struct-path-self-feature-gate.rs b/src/test/compile-fail/struct-path-self-feature-gate.rs
new file mode 100644
index 00000000000..a2050182a7e
--- /dev/null
+++ b/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() {}
diff --git a/src/test/compile-fail/struct-path-self-type-mismatch.rs b/src/test/compile-fail/struct-path-self-type-mismatch.rs
index f694e7d277c..8352bd6751f 100644
--- a/src/test/compile-fail/struct-path-self-type-mismatch.rs
+++ b/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(); }
diff --git a/src/test/compile-fail/struct-path-self.rs b/src/test/compile-fail/struct-path-self.rs
index 067d6ac22dc..aeac199227b 100644
--- a/src/test/compile-fail/struct-path-self.rs
+++ b/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 {
diff --git a/src/test/run-pass/struct-path-associated-type.rs b/src/test/run-pass/struct-path-associated-type.rs
index b033ed5c802..292761dfd00 100644
--- a/src/test/run-pass/struct-path-associated-type.rs
+++ b/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,
diff --git a/src/test/run-pass/struct-path-self.rs b/src/test/run-pass/struct-path-self.rs
index c7a282c2a2f..b569ab62c1b 100644
--- a/src/test/run-pass/struct-path-self.rs
+++ b/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> {