add member constraints tests

tests/ui/impl-trait/member-constraints/apply_member_constraint-no-req-eq.rs

@@ -0,0 +1,24 @@
+//@ check-pass
+// FIXME(-Znext-solver): enable this test
+
+trait Id {
+    type This;
+}
+impl<T> Id for T {
+    type This = T;
+}
+
+// We have two member constraints here:
+//
+// - 'unconstrained member ['a, 'static]
+// - 'unconstrained member ['static]
+//
+// Applying the first constraint results in `'unconstrained: 'a`
+// while the second then adds `'unconstrained: 'static`. If applying
+// member constraints were to require the member region equal to the
+// choice region, applying the first constraint first and then the
+// second would result in a `'a: 'static` requirement.
+fn test<'a>() -> impl Id<This = impl Sized + use<>> + use<'a> {
+    &()
+}
+fn main() {}

tests/ui/impl-trait/member-constraints/incomplete-constraint.rs

@@ -0,0 +1,21 @@
+//@ check-pass
+// FIXME(-Znext-solver): enable this test
+
+// These functions currently do not normalize the opaque type but will do
+// so in the future. At this point we've got a new use of the opaque with fully
+// universal arguments but for which lifetimes in the hidden type are unconstrained.
+//
+// Applying the member constraints would then incompletely infer `'unconstrained` to `'static`.
+fn new_defining_use<F: FnOnce(T) -> R, T, R>(_: F) {}
+
+fn rpit1<'a,  'b: 'b>(x: &'b ()) -> impl Sized + use<'a, 'b> {
+    new_defining_use(rpit1::<'a, 'b>);
+    x
+}
+
+struct Inv<'a, 'b>(*mut (&'a (), &'b ()));
+fn rpit2<'a>(_: ()) -> impl Sized + use<'a> {
+    new_defining_use(rpit2::<'a>);
+    Inv::<'a, 'static>(std::ptr::null_mut())
+}
+fn main() {}

tests/ui/nll/member-constraints/nested-impl-trait-pass.rs → tests/ui/impl-trait/member-constraints/nested-impl-trait-pass.rs

@@ -1,14 +1,17 @@
 // Nested impl-traits can impose different member constraints on the same region variable.
 
 //@ check-pass
+// FIXME(-Znext-solver): enable this test
 
 trait Cap<'a> {}
 impl<T> Cap<'_> for T {}
 
 // Assuming the hidden type is `[&'?15 u8; 1]`, we have two distinct member constraints:
 // - '?15 member ['static, 'a, 'b] // from outer impl-trait
 // - '?15 member ['static, 'a]     // from inner impl-trait
-// To satisfy both we can only choose 'a.
+// To satisfy both we can only choose 'a. Concretely, first member constraint requires ?15
+// to outlive at least 'b while the second requires ?15 to outlive 'a. As 'a outlives 'b we
+// end up with 'a as the final member region.
 fn pass_early_bound<'s, 'a, 'b>(a: &'s u8) -> impl IntoIterator<Item = impl Cap<'a>> + Cap<'b>
 where
     's: 'a,

tests/ui/impl-trait/member-constraints/reject-choice-due-to-prev-constraint.rs

@@ -0,0 +1,34 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+// We've got `'0 member ['a, 'b, 'static]` and `'1 member ['a, 'b, 'static]`.
+//
+// As '0 gets outlived by 'a - its "upper bound" -  the only applicable choice
+// region is 'a.
+//
+// '1 has to outlive 'b so the only applicable choice regions are 'b and 'static.
+// Considering this member constraint by itself would choose 'b as it is the
+// smaller of the two regions.
+//
+// However, this is only the case when ignoring the member constraint on '0.
+// After applying this constraint and requiring '0 to outlive 'a. As '1 outlives
+// '0, the region 'b is no longer an applicable choice region for '1 as 'b does
+// does not outlive 'a. We would therefore choose 'static.
+//
+// This means applying member constraints is order dependent. We handle this by
+// first applying member constraints for regions 'x and then consider the resulting
+// constraints when applying member constraints for regions 'y with 'y: 'x.
+fn with_constraints<'r0, 'r1, 'a, 'b>() -> *mut (&'r0 (), &'r1 ())
+where
+    'r1: 'r0,
+    'a: 'r0,
+    'r1: 'b,
+{
+    loop {}
+}
+fn foo<'a, 'b>() -> impl Sized + use<'a, 'b> {
+    with_constraints::<'_, '_, 'a, 'b>()
+}
+fn main() {}

tests/ui/impl-trait/no-anonymize-regions.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+// FIXME(-Znext-solver): enable this test
+
+// A regression test for an error in `redis` while working on #139587.
+//
+// We check for structural equality when adding defining uses of opaques.
+// In this test one defining use had anonymized regions while the other
+// one did not, causing an error.
+struct W<T>(T);
+fn constrain<F: FnOnce(T) -> R, T, R>(f: F) -> R {
+    loop {}
+}
+fn foo<'a>(x: for<'b> fn(&'b ())) -> impl Sized + use<'a> {
+    let mut r = constrain(foo::<'_>);
+    r = W(x);
+    r
+}
+fn main() {}