Added support for type placeholders (explicit requested type

inference in a type with `_` ). This enables partial type inference.

src/test/compile-fail/typeck_type_placeholder_item.rs

@@ -0,0 +1,119 @@
+// Copyright 2014 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.
+
+// This test checks that it is not possible to enable global type
+// inference by using the `_` type placeholder.
+
+fn test() -> _ { 5 }
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+fn test2() -> (_, _) { (5u, 5u) }
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+//~^^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+static TEST3: _ = "test";
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+static TEST4: _ = 145u16;
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+static TEST5: (_, _) = (1, 2);
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+//~^^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+fn test6(_: _) { }
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+fn test7(x: _) { let _x: uint = x; }
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+fn test8(_f: fn() -> _) { }
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+struct Test9;
+
+impl Test9 {
+    fn test9(&self) -> _ { () }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    fn test10(&self, _x : _) { }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+}
+
+impl Clone for Test9 {
+    fn clone(&self) -> _ { Test9 }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    fn clone_from(&mut self, other: _) { *self = Test9; }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+}
+
+struct Test10 {
+    a: _,
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    b: (_, _),
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    //~^^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+}
+
+pub fn main() {
+    fn fn_test() -> _ { 5 }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    fn fn_test2() -> (_, _) { (5u, 5u) }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    //~^^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    static FN_TEST3: _ = "test";
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    static FN_TEST4: _ = 145u16;
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    static FN_TEST5: (_, _) = (1, 2);
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    //~^^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    fn fn_test6(_: _) { }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    fn fn_test7(x: _) { let _x: uint = x; }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    fn fn_test8(_f: fn() -> _) { }
+    //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+    struct FnTest9;
+
+    impl FnTest9 {
+        fn fn_test9(&self) -> _ { () }
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+        fn fn_test10(&self, _x : _) { }
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    }
+
+    impl Clone for FnTest9 {
+        fn clone(&self) -> _ { FnTest9 }
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+
+        fn clone_from(&mut self, other: _) { *self = FnTest9; }
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    }
+
+    struct FnTest10 {
+        a: _,
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+        b: (_, _),
+        //~^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+        //~^^ ERROR the type placeholder `_` is not allowed within types on item signatures.
+    }
+
+}

src/test/compile-fail/typeck_type_placeholder_lifetime_1.rs

@@ -0,0 +1,21 @@
+// Copyright 2014 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.
+
+// This test checks that the `_` type placeholder does not react
+// badly if put as a lifetime parameter.
+
+struct Foo<'a, T> {
+    r: &'a T
+}
+
+pub fn main() {
+    let c: Foo<_, _> = Foo { r: &5u };
+    //~^ ERROR wrong number of type arguments: expected 1 but found 2
+}

src/test/compile-fail/typeck_type_placeholder_lifetime_2.rs

@@ -0,0 +1,21 @@
+// Copyright 2014 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.
+
+// This test checks that the `_` type placeholder does not react
+// badly if put as a lifetime parameter.
+
+struct Foo<'a, T> {
+    r: &'a T
+}
+
+pub fn main() {
+    let c: Foo<_, uint> = Foo { r: &5 };
+    //~^ ERROR wrong number of type arguments: expected 1 but found 2
+}

src/test/compile-fail/typeck_type_placeholder_mismatch.rs

@@ -0,0 +1,30 @@
+// Copyright 2014 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.
+
+// This test checks that genuine type errors with partial
+// type hints are understandable.
+
+struct Foo<T>;
+struct Bar<U>;
+
+pub fn main() {
+}
+
+fn test1() {
+    let x: Foo<_> = Bar::<uint>;
+    //~^ ERROR mismatched types: expected `Foo<<generic #0>>` but found `Bar<uint>`
+    let y: Foo<uint> = x;
+}
+
+fn test2() {
+    let x: Foo<_> = Bar::<uint>;
+    //~^ ERROR mismatched types: expected `Foo<<generic #0>>` but found `Bar<uint>`
+    //~^^ ERROR cannot determine a type for this local variable: unconstrained type
+}

src/test/run-pass/typeck_type_placeholder_1.rs

@@ -0,0 +1,32 @@
+// Copyright 2014 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.
+
+// This test checks that the `_` type placeholder works
+// correctly for enabling type inference.
+
+static CONSTEXPR: *int = &'static 413 as *_;
+
+pub fn main() {
+    use std::vec_ng::Vec;
+
+    let x: Vec<_> = range(0u, 5).collect();
+    assert_eq!(x.as_slice(), &[0u,1,2,3,4]);
+
+    let x = range(0u, 5).collect::<Vec<_>>();
+    assert_eq!(x.as_slice(), &[0u,1,2,3,4]);
+
+    let y: _ = "hello";
+    assert_eq!(y.len(), 5);
+
+    let ptr = &5u;
+    let ptr2 = ptr as *_;
+
+    assert_eq!(ptr as *uint as uint, ptr2 as uint);
+}