Add regression test for #155977

tests/ui/traits/next-solver/normalize/higher-ranked-param-env-normalization-155977.rs

@@ -0,0 +1,19 @@
+//@ compile-flags: -Znext-solver
+
+// Regression test for #155977: the new solver used to ICE while normalizing
+// a higher-ranked where-clause in the param env.
+// Fixed by eager param-env normalization in #156976.
+
+trait Trait<Input> {
+    type Output;
+}
+
+fn walk2<F>()
+//~^ ERROR the trait bound
+where
+    for<'a> F: 'a,
+    for<'a> <F as Trait<&'a u32>>::Output: 'a,
+{
+}
+
+fn main() {}

tests/ui/traits/next-solver/normalize/higher-ranked-param-env-normalization-155977.stderr

@@ -0,0 +1,18 @@
+error[E0277]: the trait bound `for<'a> F: Trait<&'a u32>` is not satisfied
+  --> $DIR/higher-ranked-param-env-normalization-155977.rs:11:1
+   |
+LL | / fn walk2<F>()
+LL | |
+LL | | where
+LL | |     for<'a> F: 'a,
+LL | |     for<'a> <F as Trait<&'a u32>>::Output: 'a,
+   | |______________________________________________^ the trait `for<'a> Trait<&'a u32>` is not implemented for `F`
+   |
+help: consider further restricting type parameter `F` with trait `Trait`
+   |
+LL |     for<'a> F: 'a + for<'a> Trait<&'a u32>,
+   |                   ++++++++++++++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.