Add tests for `auto trait`, fix parsing bug

Now we can do the well formedness checks in the parser, yay!

src/libsyntax/feature_gate.rs

@@ -1394,7 +1394,7 @@ fn visit_item(&mut self, i: &'a ast::Item) {
                                    i.span,
                                    "auto traits are experimental and possibly buggy");
             }
-            
+
             ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
                 let msg = "`macro` is experimental";
                 gate_feature_post!(&self, decl_macro, i.span, msg);

src/libsyntax/parse/parser.rs

@@ -6014,6 +6014,37 @@ fn parse_item_(&mut self, attrs: Vec<Attribute>,
                                     maybe_append(attrs, extra_attrs));
             return Ok(Some(item));
         }
+        if self.eat_keyword(keywords::Auto) {
+            self.expect_keyword(keywords::Trait)?;
+            // AUTO TRAIT ITEM
+            let (ident,
+                 item_,
+                 extra_attrs) = self.parse_item_auto_trait(ast::Unsafety::Normal)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.check_keyword(keywords::Unsafe) &&
+            self.look_ahead(1, |t| t.is_keyword(keywords::Auto)) {
+            self.expect_keyword(keywords::Unsafe)?;
+            self.expect_keyword(keywords::Auto)?;
+            self.expect_keyword(keywords::Trait)?;
+            // UNSAFE AUTO TRAIT ITEM
+            let (ident,
+                 item_,
+                 extra_attrs) = self.parse_item_auto_trait(ast::Unsafety::Unsafe)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
         if (self.check_keyword(keywords::Unsafe) &&
             self.look_ahead(1, |t| t.is_keyword(keywords::Impl))) ||
            (self.check_keyword(keywords::Default) &&
@@ -6138,37 +6169,6 @@ fn parse_item_(&mut self, attrs: Vec<Attribute>,
                                     maybe_append(attrs, extra_attrs));
             return Ok(Some(item));
         }
-        if self.eat_keyword(keywords::Auto) {
-            self.expect_keyword(keywords::Trait)?;
-            // AUTO TRAIT ITEM
-            let (ident,
-                 item_,
-                 extra_attrs) = self.parse_item_auto_trait(ast::Unsafety::Normal)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.check_keyword(keywords::Unsafe) &&
-            self.look_ahead(1, |t| t.is_keyword(keywords::Auto)) {
-            self.expect_keyword(keywords::Unsafe)?;
-            self.expect_keyword(keywords::Auto)?;
-            self.expect_keyword(keywords::Trait)?;
-            // UNSAFE AUTO TRAIT ITEM
-            let (ident,
-                 item_,
-                 extra_attrs) = self.parse_item_auto_trait(ast::Unsafety::Unsafe)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
         if self.eat_keyword(keywords::Struct) {
             // STRUCT ITEM
             let (ident, item_, extra_attrs) = self.parse_item_struct()?;

src/test/compile-fail/auto-is-contextual.rs

+// Copyright 2017 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.
+
+type A0 = auto;
+//~^ ERROR cannot find type `auto` in this scope
+type A1 = auto::auto;
+//~^ ERROR Use of undeclared type or module `auto`
+type A2 = auto<auto, auto>;
+//~^ ERROR cannot find type `auto` in this scope
+//~| ERROR cannot find type `auto` in this scope
+//~| ERROR cannot find type `auto` in this scope
+type A3 = auto<<auto as auto>::auto>;
+//~^ ERROR cannot find type `auto` in this scope
+//~| ERROR cannot find type `auto` in this scope
+//~| ERROR Use of undeclared type or module `auto`
+type A4 = auto(auto, auto) -> auto;
+//~^ ERROR cannot find type `auto` in this scope
+//~| ERROR cannot find type `auto` in this scope
+//~| ERROR cannot find type `auto` in this scope
+//~| ERROR cannot find type `auto` in this scope
+
+fn main() {}

src/test/compile-fail/feature-gate-optin-builtin-traits.rs

@@ -17,6 +17,9 @@ trait DummyTrait {
     fn dummy(&self) {}
 }
 
+auto trait AutoDummyTrait {}
+//~^ ERROR auto traits are experimental and possibly buggy
+
 impl DummyTrait for .. {}
 //~^ ERROR auto trait implementations are experimental and possibly buggy
 

src/test/parse-fail/auto-trait-no-generics.rs

+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+auto trait Auto<T> { }
+//~^ ERROR: expected `{`, found `<`

src/test/parse-fail/auto-trait-no-rename.rs

+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+auto trait Auto { fn item() }
+//~^ ERROR: expected `}`, found `fn`

src/test/parse-fail/auto-trait-no-super.rs

+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+auto trait Auto : Send { }
+//~^ ERROR: expected `{`, found `:`

src/test/run-pass/auto-traits.rs

+// Copyright 2017 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.
+
+#![feature(optin_builtin_traits)]
+
+auto trait Auto {}
+// Redundant but accepted until we remove it.
+impl Auto for .. {}
+
+unsafe auto trait AutoUnsafe {}
+
+impl !Auto for bool {}
+impl !AutoUnsafe for bool {}
+
+struct AutoBool(bool);
+
+impl Auto for AutoBool {}
+unsafe impl AutoUnsafe for AutoBool {}
+
+fn take_auto<T: Auto>(_: T) {}
+fn take_auto_unsafe<T: AutoUnsafe>(_: T) {}
+
+fn main() {
+    take_auto(0);
+    take_auto(AutoBool(true));
+    take_auto_unsafe(0);
+    take_auto_unsafe(AutoBool(true));
+}