introduce a unit testing feature `rustc_evaluate_where_clauses`

This attribute will cause us to invoke evaluate on every where clause of an
invoked function and to generate an error with the result.

Without this, it is very difficult to observe the effects of invoking the trait
evaluator.

3 files changed, 135 insertions, 0 deletions

diff --git a/src/test/ui/cycle-me.rs b/src/test/ui/cycle-me.rs
new file mode 100644
index 00000000000..eb1ffe51ffc
--- /dev/null
+++ b/src/test/ui/cycle-me.rs
@@ -0,0 +1,31 @@
+#![feature(rustc_attrs)]
+
+// A (reached depth 0)
+//   ...
+//      B // depth 1 -- reached depth = 0
+//          C // depth 2 -- reached depth = 1 (should be 0)
+//              B
+//          A // depth 0
+//   D (reached depth 1)
+//      C (cache -- reached depth = 2)
+
+struct A {
+    b: B,
+    c: C,
+}
+
+struct B {
+    c: C,
+    a: Option<Box<A>>,
+}
+
+struct C {
+    b: Option<Box<B>>,
+}
+
+#[rustc_evaluate_where_clauses]
+fn test<X: Send>() {}
+
+fn main() {
+    test::<A>();
+}
diff --git a/src/test/ui/traits/issue-83538-tainted-cache-after-cycle.rs b/src/test/ui/traits/issue-83538-tainted-cache-after-cycle.rs
new file mode 100644
index 00000000000..1b357575cb8
--- /dev/null
+++ b/src/test/ui/traits/issue-83538-tainted-cache-after-cycle.rs
@@ -0,0 +1,66 @@
+// Regression test for issue #83538. The problem here is that we have
+// two cycles:
+//
+// * `Ty` embeds `Box<Ty>` indirectly, which depends on `Global: 'static`, which is OkModuloRegions.
+// * But `Ty` also references `First`, which has a cycle on itself. That should just be `Ok`.
+//
+// But our caching mechanism was blending both cycles and giving the incorrect result.
+
+#![feature(rustc_attrs)]
+#![allow(bad_style)]
+
+struct First {
+    b: Vec<First>,
+}
+
+pub struct Second {
+    d: Vec<First>,
+}
+
+struct Third<f> {
+    g: Vec<f>,
+}
+
+enum Ty {
+    j(Fourth, Fifth, Sixth),
+}
+
+struct Fourth {
+    o: Vec<Ty>,
+}
+
+struct Fifth {
+    bounds: First,
+}
+
+struct Sixth {
+    p: Box<Ty>,
+}
+
+#[rustc_evaluate_where_clauses]
+fn forward()
+where
+    Vec<First>: Unpin,
+    Third<Ty>: Unpin,
+{
+}
+
+#[rustc_evaluate_where_clauses]
+fn reverse()
+where
+    Third<Ty>: Unpin,
+    Vec<First>: Unpin,
+{
+}
+
+fn main() {
+    // The only ERROR included here is the one that is totally wrong:
+
+    forward();
+    //~^ ERROR evaluate(Binder(TraitPredicate(<std::vec::Vec<First> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+    //~| ERROR evaluate(Binder(TraitPredicate(<Third<Ty> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+
+    reverse();
+    //~^ ERROR evaluate(Binder(TraitPredicate(<std::vec::Vec<First> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+    //~| ERROR evaluate(Binder(TraitPredicate(<Third<Ty> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+}
diff --git a/src/test/ui/traits/issue-83538-tainted-cache-after-cycle.stderr b/src/test/ui/traits/issue-83538-tainted-cache-after-cycle.stderr
new file mode 100644
index 00000000000..82e00c3b97f
--- /dev/null
+++ b/src/test/ui/traits/issue-83538-tainted-cache-after-cycle.stderr
@@ -0,0 +1,38 @@
+error: evaluate(Binder(TraitPredicate(<std::vec::Vec<First> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+  --> $DIR/issue-83538-tainted-cache-after-cycle.rs:59:5
+   |
+LL |     Vec<First>: Unpin,
+   |                 ----- predicate
+...
+LL |     forward();
+   |     ^^^^^^^
+
+error: evaluate(Binder(TraitPredicate(<Third<Ty> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+  --> $DIR/issue-83538-tainted-cache-after-cycle.rs:59:5
+   |
+LL |     Third<Ty>: Unpin,
+   |                ----- predicate
+...
+LL |     forward();
+   |     ^^^^^^^
+
+error: evaluate(Binder(TraitPredicate(<Third<Ty> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+  --> $DIR/issue-83538-tainted-cache-after-cycle.rs:63:5
+   |
+LL |     Third<Ty>: Unpin,
+   |                ----- predicate
+...
+LL |     reverse();
+   |     ^^^^^^^
+
+error: evaluate(Binder(TraitPredicate(<std::vec::Vec<First> as std::marker::Unpin>), [])) = Ok(EvaluatedToOkModuloRegions)
+  --> $DIR/issue-83538-tainted-cache-after-cycle.rs:63:5
+   |
+LL |     Vec<First>: Unpin,
+   |                 ----- predicate
+...
+LL |     reverse();
+   |     ^^^^^^^
+
+error: aborting due to 4 previous errors
+