Ignore but do not assume region obligations from unifying headers in negative coherence

2 files changed, 44 insertions, 0 deletions

diff --git a/tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.explicit.stderr b/tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.explicit.stderr
new file mode 100644
index 00000000000..34f3904443c
--- /dev/null
+++ b/tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.explicit.stderr
@@ -0,0 +1,19 @@
+error: conflicting implementations of trait `FnMarker` for type `fn(&_)`
+  --> $DIR/negative-coherence-placeholder-region-constraints-on-unification.rs:21:1
+   |
+LL | impl<T: ?Sized + Marker> FnMarker for fn(T) {}
+   | ------------------------------------------- first implementation here
+LL | impl<T: ?Sized> FnMarker for fn(&T) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `fn(&_)`
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #56105 <https://github.com/rust-lang/rust/issues/56105>
+   = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
+note: the lint level is defined here
+  --> $DIR/negative-coherence-placeholder-region-constraints-on-unification.rs:4:11
+   |
+LL | #![forbid(coherence_leak_check)]
+   |           ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.rs b/tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.rs
new file mode 100644
index 00000000000..26d9d84d8f0
--- /dev/null
+++ b/tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.rs
@@ -0,0 +1,25 @@
+// revisions: explicit implicit
+//[implicit] check-pass
+
+#![forbid(coherence_leak_check)]
+#![feature(negative_impls, with_negative_coherence)]
+
+pub trait Marker {}
+
+#[cfg(implicit)]
+impl<T: ?Sized> !Marker for &T {}
+
+#[cfg(explicit)]
+impl<'a, T: ?Sized + 'a> !Marker for &'a T {}
+
+trait FnMarker {}
+
+// Unifying these two impls below results in a `T: '!0` obligation
+// that we shouldn't need to care about. Ideally, we'd treat that
+// as an assumption when proving `&'!0 T: Marker`...
+impl<T: ?Sized + Marker> FnMarker for fn(T) {}
+impl<T: ?Sized> FnMarker for fn(&T) {}
+//[explicit]~^ ERROR conflicting implementations of trait `FnMarker` for type `fn(&_)`
+//[explicit]~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+fn main() {}