Introduce the new phantomdata/phantomfn markers and integrate them

into variance inference; fix various bugs in variance inference
so that it considers the correct set of constraints; modify infer to
consider the results of variance inference for type arguments.

src/test/compile-fail/variance-contravariant-arg-object.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get<T> : 'static {
+    fn get(&self, t: T);
+}
+
+fn get_min_from_max<'min, 'max>(v: Box<Get<&'max i32>>)
+                                -> Box<Get<&'min i32>>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+fn get_max_from_min<'min, 'max, G>(v: Box<Get<&'min i32>>)
+                                   -> Box<Get<&'max i32>>
+    where 'max : 'min
+{
+    v
+}
+
+fn main() { }

src/test/compile-fail/variance-contravariant-arg-trait-match.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get<T> {
+    fn get(&self, t: T);
+}
+
+fn get_min_from_max<'min, 'max, G>()
+    where 'max : 'min, G : Get<&'max i32>
+{
+    impls_get::<G,&'min i32>() //~ ERROR mismatched types
+}
+
+fn get_max_from_min<'min, 'max, G>()
+    where 'max : 'min, G : Get<&'min i32>
+{
+    impls_get::<G,&'max i32>()
+}
+
+fn impls_get<G,T>() where G : Get<T> { }
+
+fn main() { }

src/test/compile-fail/variance-contravariant-self-trait-match.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get {
+    fn get(&self);
+}
+
+fn get_min_from_max<'min, 'max, G>()
+    where 'max : 'min, G : 'max, &'max G : Get
+{
+    impls_get::<&'min G>(); //~ ERROR mismatched types
+}
+
+fn get_max_from_min<'min, 'max, G>()
+    where 'max : 'min, G : 'max, &'min G : Get
+{
+    impls_get::<&'max G>();
+}
+
+fn impls_get<G>() where G : Get { }
+
+fn main() { }

src/test/compile-fail/variance-covariant-arg-object.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get<T> : 'static {
+    fn get(&self) -> T;
+}
+
+fn get_min_from_max<'min, 'max>(v: Box<Get<&'max i32>>)
+                                -> Box<Get<&'min i32>>
+    where 'max : 'min
+{
+    v
+}
+
+fn get_max_from_min<'min, 'max, G>(v: Box<Get<&'min i32>>)
+                                   -> Box<Get<&'max i32>>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+fn main() { }

src/test/compile-fail/variance-covariant-arg-trait-match.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get<T> {
+    fn get(&self) -> T;
+}
+
+fn get_min_from_max<'min, 'max, G>()
+    where 'max : 'min, G : Get<&'max i32>
+{
+    impls_get::<G,&'min i32>()
+}
+
+fn get_max_from_min<'min, 'max, G>()
+    where 'max : 'min, G : Get<&'min i32>
+{
+    impls_get::<G,&'max i32>() //~ ERROR mismatched types
+}
+
+fn impls_get<G,T>() where G : Get<T> { }
+
+fn main() { }

src/test/compile-fail/variance-covariant-self-trait-match.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get {
+    fn get() -> Self;
+}
+
+fn get_min_from_max<'min, 'max, G>()
+    where 'max : 'min, G : 'max, &'max G : Get
+{
+    impls_get::<&'min G>();
+}
+
+fn get_max_from_min<'min, 'max, G>()
+    where 'max : 'min, G : 'max, &'min G : Get
+{
+    impls_get::<&'max G>(); //~ ERROR mismatched types
+}
+
+fn impls_get<G>() where G : Get { }
+
+fn main() { }

src/test/compile-fail/variance-invariant-arg-object.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get<T> : 'static {
+    fn get(&self, t: T) -> T;
+}
+
+fn get_min_from_max<'min, 'max>(v: Box<Get<&'max i32>>)
+                                -> Box<Get<&'min i32>>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+fn get_max_from_min<'min, 'max, G>(v: Box<Get<&'min i32>>)
+                                   -> Box<Get<&'max i32>>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+fn main() { }

src/test/compile-fail/variance-invariant-arg-trait-match.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get<T> {
+    fn get(&self, t: T) -> T;
+}
+
+fn get_min_from_max<'min, 'max, G>()
+    where 'max : 'min, G : Get<&'max i32>
+{
+    impls_get::<G,&'min i32>() //~ ERROR mismatched types
+}
+
+fn get_max_from_min<'min, 'max, G>()
+    where 'max : 'min, G : Get<&'min i32>
+{
+    impls_get::<G,&'max i32>() //~ ERROR mismatched types
+}
+
+fn impls_get<G,T>() where G : Get<T> { }
+
+fn main() { }

src/test/compile-fail/variance-invariant-self-trait-match.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+trait Get {
+    fn get(&self) -> Self;
+}
+
+fn get_min_from_max<'min, 'max, G>()
+    where 'max : 'min, &'max G : Get
+{
+    impls_get::<&'min G>(); //~ ERROR mismatched types
+}
+
+fn get_max_from_min<'min, 'max, G>()
+    where 'max : 'min, &'min G : Get
+{
+    impls_get::<&'max G>(); //~ ERROR mismatched types
+}
+
+fn impls_get<G>() where G : Get { }
+
+fn main() { }

src/test/compile-fail/variance-regions-unused-direct.rs

@@ -0,0 +1,25 @@
+// Copyright 2012 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.
+
+// Test that disallow lifetime parameters that are unused.
+
+use std::marker;
+
+struct Bivariant<'a>; //~ ERROR parameter `'a` is never used
+
+struct Struct<'a, 'd> { //~ ERROR parameter `'d` is never used
+    field: &'a [i32]
+}
+
+trait Trait<'a, 'd> { //~ ERROR parameter `'d` is never used
+    fn method(&'a self);
+}
+
+fn main() {}

src/test/compile-fail/variance-regions-unused-indirect.rs

@@ -0,0 +1,21 @@
+// Copyright 2012 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.
+
+// Test that disallow lifetime parameters that are unused.
+
+enum Foo<'a> { //~ ERROR parameter `'a` is never used
+    Foo1(Bar<'a>)
+}
+
+enum Bar<'a> { //~ ERROR parameter `'a` is never used
+    Bar1(Foo<'a>)
+}
+
+fn main() {}

src/test/compile-fail/variance-trait-bounds.rs

@@ -0,0 +1,64 @@
+// 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.
+
+#![deny(bivariance)]
+#![allow(dead_code)]
+
+// Check that bounds on type parameters (other than `Self`) do not
+// influence variance.
+
+#[rustc_variance]
+trait Getter<T> { //~ ERROR types=[[+];[-];[]]
+    fn get(&self) -> T;
+}
+
+#[rustc_variance]
+trait Setter<T> { //~ ERROR types=[[-];[-];[]]
+    fn get(&self, T);
+}
+
+#[rustc_variance]
+struct TestStruct<U,T:Setter<U>> { //~ ERROR types=[[+, +];[];[]]
+    t: T, u: U
+}
+
+#[rustc_variance]
+enum TestEnum<U,T:Setter<U>> {//~ ERROR types=[[*, +];[];[]]
+    //~^ ERROR parameter `U` is never used
+    Foo(T)
+}
+
+#[rustc_variance]
+trait TestTrait<U,T:Setter<U>> { //~ ERROR types=[[-, +];[-];[]]
+    fn getter(&self, u: U) -> T;
+}
+
+#[rustc_variance]
+trait TestTrait2<U> : Getter<U> { //~ ERROR types=[[+];[-];[]]
+}
+
+#[rustc_variance]
+trait TestTrait3<U> { //~ ERROR types=[[-];[-];[]]
+    fn getter<T:Getter<U>>(&self);
+}
+
+#[rustc_variance]
+struct TestContraStruct<U,T:Setter<U>> { //~ ERROR types=[[*, +];[];[]]
+    //~^ ERROR parameter `U` is never used
+    t: T
+}
+
+#[rustc_variance]
+struct TestBox<U,T:Getter<U>+Setter<U>> { //~ ERROR types=[[*, +];[];[]]
+    //~^ ERROR parameter `U` is never used
+    t: T
+}
+
+pub fn main() { }

src/test/compile-fail/variance-types-bounds.rs

@@ -0,0 +1,74 @@
+// Copyright 2012 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.
+
+// Test that we correctly infer variance for type parameters in
+// various types and traits.
+
+#[rustc_variance]
+struct TestImm<A, B> { //~ ERROR types=[[+, +];[];[]]
+    x: A,
+    y: B,
+}
+
+#[rustc_variance]
+struct TestMut<A, B:'static> { //~ ERROR types=[[+, o];[];[]]
+    x: A,
+    y: &'static mut B,
+}
+
+#[rustc_variance]
+struct TestIndirect<A:'static, B:'static> { //~ ERROR types=[[+, o];[];[]]
+    m: TestMut<A, B>
+}
+
+#[rustc_variance]
+struct TestIndirect2<A:'static, B:'static> { //~ ERROR types=[[o, o];[];[]]
+    n: TestMut<A, B>,
+    m: TestMut<B, A>
+}
+
+#[rustc_variance]
+trait Getter<A> { //~ ERROR types=[[+];[-];[]]
+    fn get(&self) -> A;
+}
+
+#[rustc_variance]
+trait Setter<A> { //~ ERROR types=[[-];[o];[]]
+    fn set(&mut self, a: A);
+}
+
+#[rustc_variance]
+trait GetterSetter<A> { //~ ERROR types=[[o];[o];[]]
+    fn get(&self) -> A;
+    fn set(&mut self, a: A);
+}
+
+#[rustc_variance]
+trait GetterInTypeBound<A> { //~ ERROR types=[[-];[-];[]]
+    // Here, the use of `A` in the method bound *does* affect
+    // variance.  Think of it as if the method requested a dictionary
+    // for `T:Getter<A>`.  Since this dictionary is an input, it is
+    // contravariant, and the Getter is covariant w/r/t A, yielding an
+    // overall contravariant result.
+    fn do_it<T:Getter<A>>(&self);
+}
+
+#[rustc_variance]
+trait SetterInTypeBound<A> { //~ ERROR types=[[+];[-];[]]
+    fn do_it<T:Setter<A>>(&self);
+}
+
+#[rustc_variance]
+struct TestObject<A, R> { //~ ERROR types=[[-, +];[];[]]
+    n: Box<Setter<A>+Send>,
+    m: Box<Getter<R>+Send>,
+}
+
+fn main() {}

src/test/compile-fail/variance-types.rs

@@ -0,0 +1,51 @@
+// 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.
+
+#![deny(bivariance)]
+#![allow(dead_code)]
+
+use std::cell::Cell;
+
+// Check that a type parameter which is only used in a trait bound is
+// not considered bivariant.
+
+#[rustc_variance]
+struct InvariantMut<'a,A:'a,B:'a> { //~ ERROR types=[[o, o];[];[]], regions=[[-];[];[]]
+    t: &'a mut (A,B)
+}
+
+#[rustc_variance]
+struct InvariantCell<A> { //~ ERROR types=[[o];[];[]]
+    t: Cell<A>
+}
+
+#[rustc_variance]
+struct InvariantIndirect<A> { //~ ERROR types=[[o];[];[]]
+    t: InvariantCell<A>
+}
+
+#[rustc_variance]
+struct Covariant<A> { //~ ERROR types=[[+];[];[]]
+    t: A, u: fn() -> A
+}
+
+#[rustc_variance]
+struct Contravariant<A> { //~ ERROR types=[[-];[];[]]
+    t: fn(A)
+}
+
+#[rustc_variance]
+enum Enum<A,B,C> { //~ ERROR types=[[+, -, o];[];[]]
+    Foo(Covariant<A>),
+    Bar(Contravariant<B>),
+    Zed(Covariant<C>,Contravariant<C>)
+}
+
+pub fn main() { }

src/test/compile-fail/variance-unused-region-param.rs

@@ -0,0 +1,17 @@
+// Copyright 2012 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.
+
+// Test that we report an error for unused type parameters in types.
+
+struct SomeStruct<'a> { x: u32 } //~ ERROR parameter `'a` is never used
+enum SomeEnum<'a> { Nothing } //~ ERROR parameter `'a` is never used
+trait SomeTrait<'a> { fn foo(&self); } //~ ERROR parameter `'a` is never used
+
+fn main() {}

src/test/compile-fail/variance-unused-type-param.rs

@@ -0,0 +1,36 @@
+// Copyright 2012 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.
+
+#![allow(dead_code)]
+
+// Test that we report an error for unused type parameters in types and traits,
+// and that we offer a helpful suggestion.
+
+struct SomeStruct<A> { x: u32 }
+//~^ ERROR parameter `A` is never used
+//~| HELP PhantomData
+
+enum SomeEnum<A> { Nothing }
+//~^ ERROR parameter `A` is never used
+//~| HELP PhantomData
+
+trait SomeTrait<A> { fn foo(&self); }
+//~^ ERROR parameter `A` is never used
+//~| HELP PhantomFn
+
+// Here T might *appear* used, but in fact it isn't.
+enum ListCell<T> {
+//~^ ERROR parameter `T` is never used
+//~| HELP PhantomData
+    Cons(Box<ListCell<T>>),
+    Nil
+}
+
+fn main() {}

src/test/compile-fail/variance-use-contravariant-struct-1.rs

@@ -0,0 +1,24 @@
+// Copyright 2015 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.
+
+// Test various uses of structs with distint variances to make sure
+// they permit lifetimes to be approximated as expected.
+
+struct SomeStruct<T>(fn(T));
+
+fn foo<'min,'max>(v: SomeStruct<&'max ()>)
+                  -> SomeStruct<&'min ()>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+#[rustc_error]
+fn main() { }

src/test/compile-fail/variance-use-contravariant-struct-2.rs

@@ -0,0 +1,26 @@
+// Copyright 2015 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.
+
+// Test various uses of structs with distint variances to make sure
+// they permit lifetimes to be approximated as expected.
+
+#![allow(dead_code)]
+
+struct SomeStruct<T>(fn(T));
+
+fn bar<'min,'max>(v: SomeStruct<&'min ()>)
+                  -> SomeStruct<&'max ()>
+    where 'max : 'min
+{
+    v
+}
+
+#[rustc_error]
+fn main() { } //~ ERROR compilation successful

src/test/compile-fail/variance-use-covariant-struct-1.rs

@@ -0,0 +1,23 @@
+// Copyright 2015 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.
+
+// Test that a covariant struct does not permit the lifetime of a
+// reference to be enlarged.
+
+struct SomeStruct<T>(T);
+
+fn foo<'min,'max>(v: SomeStruct<&'min ()>)
+                  -> SomeStruct<&'max ()>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+fn main() { }

src/test/compile-fail/variance-use-covariant-struct-2.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 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.
+
+// Test that a covariant struct permits the lifetime of a reference to
+// be shortened.
+
+#![allow(dead_code)]
+
+struct SomeStruct<T>(T);
+
+fn foo<'min,'max>(v: SomeStruct<&'max ()>)
+                  -> SomeStruct<&'min ()>
+    where 'max : 'min
+{
+    v
+}
+
+#[rustc_error] fn main() { } //~ ERROR compilation successful

src/test/compile-fail/variance-use-invariant-struct-1.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+// Test various uses of structs with distint variances to make sure
+// they permit lifetimes to be approximated as expected.
+
+struct SomeStruct<T>(*mut T);
+
+fn foo<'min,'max>(v: SomeStruct<&'max ()>)
+                  -> SomeStruct<&'min ()>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+fn bar<'min,'max>(v: SomeStruct<&'min ()>)
+                  -> SomeStruct<&'max ()>
+    where 'max : 'min
+{
+    v //~ ERROR mismatched types
+}
+
+#[rustc_error]
+fn main() { }

src/test/run-pass/variance-intersection-of-ref-and-opt-ref.rs

@@ -0,0 +1,34 @@
+// Copyright 2015 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.
+
+// Elaborated version of the opening example from RFC 738. This failed
+// to compile before variance because invariance of `Option` prevented
+// us from approximating the lifetimes of `field1` and `field2` to a
+// common intersection.
+
+#![allow(dead_code)]
+
+struct List<'l> {
+    field1: &'l i32,
+    field2: Option<&'l i32>,
+}
+
+fn foo(field1: &i32, field2: Option<&i32>) -> i32 {
+    let list = List { field1: field1, field2: field2 };
+    *list.field1 + list.field2.cloned().unwrap_or(0)
+}
+
+fn main() {
+    let x = 22;
+    let y = Some(3);
+    let z = None;
+    assert_eq!(foo(&x, y.as_ref()), 25);
+    assert_eq!(foo(&x, z.as_ref()), 22);
+}

src/test/run-pass/variance-trait-matching.rs

@@ -0,0 +1,49 @@
+// Copyright 2015 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.
+
+#![allow(dead_code)]
+
+// Get<T> is covariant in T
+trait Get<T> {
+    fn get(&self) -> T;
+}
+
+struct Cloner<T:Clone> {
+    t: T
+}
+
+impl<T:Clone> Get<T> for Cloner<T> {
+    fn get(&self) -> T {
+        self.t.clone()
+    }
+}
+
+fn get<'a, G>(get: &G) -> i32
+    where G : Get<&'a i32>
+{
+    // This call only type checks if we can use `G : Get<&'a i32>` as
+    // evidence that `G : Get<&'b i32>` where `'a : 'b`.
+    pick(get, &22)
+}
+
+fn pick<'b, G>(get: &'b G, if_odd: &'b i32) -> i32
+    where G : Get<&'b i32>
+{
+    let v = *get.get();
+    if v % 2 != 0 { v } else { *if_odd }
+}
+
+fn main() {
+    let x = Cloner { t: &23 };
+    let y = get(&x);
+    assert_eq!(y, 23);
+}
+
+

src/test/run-pass/variance-vec-covariant.rs

@@ -0,0 +1,28 @@
+// Copyright 2015 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.
+
+// Test that vec is now covariant in its argument type.
+
+#![allow(dead_code)]
+
+fn foo<'a,'b>(v1: Vec<&'a i32>, v2: Vec<&'b i32>) -> i32 {
+    bar(v1, v2).cloned().unwrap_or(0) // only type checks if we can intersect 'a and 'b
+}
+
+fn bar<'c>(v1: Vec<&'c i32>, v2: Vec<&'c i32>) -> Option<&'c i32> {
+    v1.get(0).cloned().or_else(|| v2.get(0).cloned())
+}
+
+fn main() {
+    let x = 22;
+    let y = 44;
+    assert_eq!(foo(vec![&x], vec![&y]), 22);
+    assert_eq!(foo(vec![&y], vec![&x]), 44);
+}