Auto merge of #54624 - arielb1:evaluate-outlives, r=nikomatsakis

handle outlives predicates in trait evaluation

This handles higher-ranked outlives predicates in trait evaluation the same way they are handled in projection.

Fixes #54302. I think this is a more correct fix than #54401 because it fixes the root case in evaluation instead of making evaluation used in less cases. However, we might want to go to a direction closer to @nikomatsakis's solution with Chalk.

r? @nikomatsakis

src/test/ui/issue-54302-cases.rs

@@ -0,0 +1,95 @@
+// Copyright 2018 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.
+
+trait Mirror {
+    type Image;
+    fn coerce(self) -> Self::Image;
+}
+
+impl<T> Mirror for T {
+    type Image = T;
+    fn coerce(self) -> Self { self }
+}
+
+trait Foo<'x, T> {
+    fn foo(self) -> &'x T;
+}
+
+impl<'s, 'x, T: 'x> Foo<'x, T> for &'s T where &'s T: Foo2<'x, T> {
+    fn foo(self) -> &'x T { self.foo2() }
+}
+
+trait Foo2<'x, T> {
+    fn foo2(self) -> &'x T;
+}
+
+// example 1 - fails leak check
+impl<'x> Foo2<'x, u32> for &'x u32
+{
+    fn foo2(self) -> &'x u32 { self }
+}
+
+// example 2 - OK with this issue
+impl<'x, 'a: 'x> Foo2<'x, i32> for &'a i32
+{
+    fn foo2(self) -> &'x i32 { self }
+}
+
+// example 3 - fails due to issue #XYZ + Leak-check
+impl<'x, T> Foo2<'x, u64> for T
+    where T: Mirror<Image=&'x u64>
+{
+    fn foo2(self) -> &'x u64 { self.coerce() }
+}
+
+// example 4 - fails due to issue #XYZ
+impl<'x, 'a: 'x, T> Foo2<'x, i64> for T
+    where T: Mirror<Image=&'a i64>
+{
+    fn foo2(self) -> &'x i64 { self.coerce() }
+}
+
+
+trait RefFoo<T> {
+    fn ref_foo(&self) -> &'static T;
+}
+
+impl<T> RefFoo<T> for T where for<'a> &'a T: Foo<'static, T> {
+    fn ref_foo(&self) -> &'static T {
+        self.foo()
+    }
+}
+
+
+fn coerce_lifetime1(a: &u32) -> &'static u32
+{
+    <u32 as RefFoo<u32>>::ref_foo(a)
+    //~^ ERROR the trait bound `for<'a> &'a u32: Foo2<'_, u32>` is not satisfied
+}
+
+fn coerce_lifetime2(a: &i32) -> &'static i32
+{
+    <i32 as RefFoo<i32>>::ref_foo(a)
+    //~^ ERROR the requirement `for<'a> 'a : ` is not satisfied
+}
+
+fn coerce_lifetime3(a: &u64) -> &'static u64
+{
+    <u64 as RefFoo<u64>>::ref_foo(a)
+    //~^ ERROR type mismatch resolving `for<'a> <&'a u64 as Mirror>::Image == &u64`
+}
+
+fn coerce_lifetime4(a: &i64) -> &'static i64
+{
+    <i64 as RefFoo<i64>>::ref_foo(a)
+    //~^ ERROR type mismatch resolving `for<'a> <&'a i64 as Mirror>::Image == &i64`
+}
+
+fn main() {}

src/test/ui/issue-54302-cases.stderr

@@ -0,0 +1,65 @@
+error[E0277]: the trait bound `for<'a> &'a u32: Foo2<'_, u32>` is not satisfied
+  --> $DIR/issue-54302-cases.rs:73:5
+   |
+LL |     <u32 as RefFoo<u32>>::ref_foo(a)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> Foo2<'_, u32>` is not implemented for `&'a u32`
+   |
+   = help: the following implementations were found:
+             <&'x u32 as Foo2<'x, u32>>
+   = note: required because of the requirements on the impl of `for<'a> Foo<'static, u32>` for `&'a u32`
+   = note: required because of the requirements on the impl of `RefFoo<u32>` for `u32`
+note: required by `RefFoo::ref_foo`
+  --> $DIR/issue-54302-cases.rs:61:5
+   |
+LL |     fn ref_foo(&self) -> &'static T;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0279]: the requirement `for<'a> 'a : ` is not satisfied (`expected bound lifetime parameter 'a, found concrete lifetime`)
+  --> $DIR/issue-54302-cases.rs:79:5
+   |
+LL |     <i32 as RefFoo<i32>>::ref_foo(a)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: required because of the requirements on the impl of `for<'a> Foo2<'_, i32>` for `&'a i32`
+   = note: required because of the requirements on the impl of `for<'a> Foo<'static, i32>` for `&'a i32`
+   = note: required because of the requirements on the impl of `RefFoo<i32>` for `i32`
+note: required by `RefFoo::ref_foo`
+  --> $DIR/issue-54302-cases.rs:61:5
+   |
+LL |     fn ref_foo(&self) -> &'static T;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `for<'a> <&'a u64 as Mirror>::Image == &u64`
+  --> $DIR/issue-54302-cases.rs:85:5
+   |
+LL |     <u64 as RefFoo<u64>>::ref_foo(a)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected bound lifetime parameter 'a, found concrete lifetime
+   |
+   = note: required because of the requirements on the impl of `for<'a> Foo2<'_, u64>` for `&'a u64`
+   = note: required because of the requirements on the impl of `for<'a> Foo<'static, u64>` for `&'a u64`
+   = note: required because of the requirements on the impl of `RefFoo<u64>` for `u64`
+note: required by `RefFoo::ref_foo`
+  --> $DIR/issue-54302-cases.rs:61:5
+   |
+LL |     fn ref_foo(&self) -> &'static T;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `for<'a> <&'a i64 as Mirror>::Image == &i64`
+  --> $DIR/issue-54302-cases.rs:91:5
+   |
+LL |     <i64 as RefFoo<i64>>::ref_foo(a)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected bound lifetime parameter 'a, found concrete lifetime
+   |
+   = note: required because of the requirements on the impl of `for<'a> Foo2<'_, i64>` for `&'a i64`
+   = note: required because of the requirements on the impl of `for<'a> Foo<'static, i64>` for `&'a i64`
+   = note: required because of the requirements on the impl of `RefFoo<i64>` for `i64`
+note: required by `RefFoo::ref_foo`
+  --> $DIR/issue-54302-cases.rs:61:5
+   |
+LL |     fn ref_foo(&self) -> &'static T;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
+
+Some errors occurred: E0271, E0277, E0279.
+For more information about an error, try `rustc --explain E0271`.

src/test/ui/issue-54302.rs

@@ -0,0 +1,29 @@
+// Copyright 2018 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.
+
+trait Deserialize<'de> {}
+
+trait DeserializeOwned: for<'de> Deserialize<'de> {}
+impl<T> DeserializeOwned for T where T: for<'de> Deserialize<'de> {}
+
+// Based on this impl, `&'static str` only implements Deserialize<'static>.
+// It does not implement for<'de> Deserialize<'de>.
+impl<'de: 'a, 'a> Deserialize<'de> for &'a str {}
+
+fn main() {
+    // Then why does it implement DeserializeOwned? This compiles.
+    fn assert_deserialize_owned<T: DeserializeOwned>() {}
+    assert_deserialize_owned::<&'static str>();
+    //~^ ERROR the requirement `for<'de> 'de : ` is not satisfied
+
+    // It correctly does not implement for<'de> Deserialize<'de>.
+    //fn assert_hrtb<T: for<'de> Deserialize<'de>>() {}
+    //assert_hrtb::<&'static str>();
+}

src/test/ui/issue-54302.stderr

@@ -0,0 +1,17 @@
+error[E0279]: the requirement `for<'de> 'de : ` is not satisfied (`expected bound lifetime parameter 'de, found concrete lifetime`)
+  --> $DIR/issue-54302.rs:23:5
+   |
+LL |     assert_deserialize_owned::<&'static str>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: required because of the requirements on the impl of `for<'de> Deserialize<'de>` for `&'static str`
+   = note: required because of the requirements on the impl of `DeserializeOwned` for `&'static str`
+note: required by `main::assert_deserialize_owned`
+  --> $DIR/issue-54302.rs:22:5
+   |
+LL |     fn assert_deserialize_owned<T: DeserializeOwned>() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0279`.

src/test/ui/run-pass/traits/traits-static-outlives-a-where-clause.rs

@@ -0,0 +1,33 @@
+// Copyright 2018 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.
+
+// run-pass
+
+trait Foo<'a> {
+    fn xyz(self);
+}
+impl<'a, T> Foo<'a> for T where 'static: 'a {
+    fn xyz(self) {}
+}
+
+trait Bar {
+    fn uvw(self);
+}
+impl<T> Bar for T where for<'a> T: Foo<'a> {
+    fn uvw(self) { self.xyz(); }
+}
+
+fn foo<T>(t: T) where T: Bar {
+    t.uvw();
+}
+
+fn main() {
+    foo(0);
+}