diff options
| -rw-r--r-- | src/librustc/traits/select.rs | 20 | ||||
| -rw-r--r-- | src/test/ui/lub-glb/old-lub-glb-object.rs | 6 | ||||
| -rw-r--r-- | src/test/ui/lub-glb/old-lub-glb-object.stderr | 18 |
3 files changed, 38 insertions, 6 deletions
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs index 4a02b033147..05fb40ac10a 100644 --- a/src/librustc/traits/select.rs +++ b/src/librustc/traits/select.rs @@ -3315,9 +3315,27 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> { tcx.mk_existential_predicates(iter) }); let source_trait = tcx.mk_dynamic(existential_predicates, r_b); + + // Require that the traits involved in this upcast are **equal**; + // only the **lifetime bound** is changed. + // + // FIXME: This condition is arguably too strong -- it + // would suffice for the source trait to be a + // *subtype* of the target trait. In particular + // changing from something like `for<'a, 'b> Foo<'a, + // 'b>` to `for<'a> Foo<'a, 'a>` should be + // permitted. And, indeed, in the in commit + // 904a0bde93f0348f69914ee90b1f8b6e4e0d7cbc, this + // condition was loosened. However, when the leak check was added + // back, using subtype here actually guies the coercion code in + // such a way that it accepts `old-lub-glb-object.rs`. This is probably + // a good thing, but I've modified this to `.eq` because I want + // to continue rejecting that test (as we have done for quite some time) + // before we are firmly comfortable with what our behavior + // should be there. -nikomatsakis let InferOk { obligations, .. } = self.infcx .at(&obligation.cause, obligation.param_env) - .sup(target, source_trait) + .eq(target, source_trait) // FIXME -- see below .map_err(|_| Unimplemented)?; nested.extend(obligations); diff --git a/src/test/ui/lub-glb/old-lub-glb-object.rs b/src/test/ui/lub-glb/old-lub-glb-object.rs index 3e95a7111e0..dcd604a5157 100644 --- a/src/test/ui/lub-glb/old-lub-glb-object.rs +++ b/src/test/ui/lub-glb/old-lub-glb-object.rs @@ -1,9 +1,5 @@ // Test that we give a note when the old LUB/GLB algorithm would have // succeeded but the new code (which is stricter) gives an error. -// -// compile-pass -// -// TODO -- why does this test pass? trait Foo<T, U> { } @@ -13,7 +9,7 @@ fn foo( ) { let z = match 22 { 0 => x, - _ => y, + _ => y, //~ ERROR match arms have incompatible types }; } diff --git a/src/test/ui/lub-glb/old-lub-glb-object.stderr b/src/test/ui/lub-glb/old-lub-glb-object.stderr new file mode 100644 index 00000000000..056f9131dd2 --- /dev/null +++ b/src/test/ui/lub-glb/old-lub-glb-object.stderr @@ -0,0 +1,18 @@ +error[E0308]: match arms have incompatible types + --> $DIR/old-lub-glb-object.rs:12:14 + | +LL | let z = match 22 { + | _____________- +LL | | 0 => x, + | | - this is found to be of type `&dyn for<'a, 'b> Foo<&'a u8, &'b u8>` +LL | | _ => y, //~ ERROR match arms have incompatible types + | | ^ expected bound lifetime parameter 'a, found concrete lifetime +LL | | }; + | |_____- `match` arms have incompatible types + | + = note: expected type `&dyn for<'a, 'b> Foo<&'a u8, &'b u8>` + found type `&dyn for<'a> Foo<&'a u8, &'a u8>` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0308`. |