Don't assemble non-env/bound candidates if projection is rigid

2 files changed, 49 insertions, 17 deletions

diff --git a/tests/ui/impl-unused-tps.stderr b/tests/ui/impl-unused-tps.stderr
index 09c3fce641c..eff5ffff9b6 100644
--- a/tests/ui/impl-unused-tps.stderr
+++ b/tests/ui/impl-unused-tps.stderr
@@ -7,23 +7,6 @@ LL | impl<T> Foo<T> for [isize; 0] {
 LL | impl<T, U> Foo<T> for U {
    | ^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `[isize; 0]`
 
-error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:32:9
-   |
-LL | impl<T, U> Bar for T {
-   |         ^ unconstrained type parameter
-
-error[E0119]: conflicting implementations of trait `Bar`
-  --> $DIR/impl-unused-tps.rs:40:1
-   |
-LL |   impl<T, U> Bar for T {
-   |   -------------------- first implementation here
-...
-LL | / impl<T, U> Bar for T
-LL | | where
-LL | |     T: Bar<Out = U>,
-   | |____________________^ conflicting implementation
-
 error[E0119]: conflicting implementations of trait `Foo<[isize; 0]>` for type `[isize; 0]`
   --> $DIR/impl-unused-tps.rs:49:1
    |
@@ -53,6 +36,12 @@ LL | impl<T, U> Foo<T> for [isize; 1] {
    |         ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/impl-unused-tps.rs:32:9
+   |
+LL | impl<T, U> Bar for T {
+   |         ^ unconstrained type parameter
+
+error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
   --> $DIR/impl-unused-tps.rs:40:9
    |
 LL | impl<T, U> Bar for T
@@ -70,6 +59,17 @@ error[E0207]: the type parameter `V` is not constrained by the impl trait, self
 LL | impl<T, U, V> Foo<T> for T
    |            ^ unconstrained type parameter
 
+error[E0119]: conflicting implementations of trait `Bar`
+  --> $DIR/impl-unused-tps.rs:40:1
+   |
+LL |   impl<T, U> Bar for T {
+   |   -------------------- first implementation here
+...
+LL | / impl<T, U> Bar for T
+LL | | where
+LL | |     T: Bar<Out = U>,
+   | |____________________^ conflicting implementation
+
 error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0119, E0207.
diff --git a/tests/ui/traits/next-solver/rpitit-cycle-due-to-rigid.rs b/tests/ui/traits/next-solver/rpitit-cycle-due-to-rigid.rs
new file mode 100644
index 00000000000..ec3d710ef37
--- /dev/null
+++ b/tests/ui/traits/next-solver/rpitit-cycle-due-to-rigid.rs
@@ -0,0 +1,32 @@
+//@ compile-flags: -Znext-solver
+//@ check-pass
+//@ edition: 2024
+
+// Ensure we don't end up in a query cycle due to trying to assemble an impl candidate
+// for an RPITIT normalizes-to goal, even though that impl candidate would *necessarily*
+// be made rigid by a where clause. This query cycle is thus avoidable by not assembling
+// that impl candidate which we *know* we are going to throw away anyways.
+
+use std::future::Future;
+
+pub trait ReactiveFunction: Send {
+    type Output;
+
+    fn invoke(self) -> Self::Output;
+}
+
+trait AttributeValue {
+    fn resolve(self) -> impl Future<Output = ()> + Send;
+}
+
+impl<F, V> AttributeValue for F
+where
+    F: ReactiveFunction<Output = V>,
+    V: AttributeValue,
+{
+    async fn resolve(self) {
+        self.invoke().resolve().await
+    }
+}
+
+fn main() {}