[NominalFuzzing] Fix SignaturePruning on types with a super (#4657)

Do not prune parameters if there is a supertype that is a signature.

Without this we crash on an assertion in TypeBuilder when we try to
recreate the types (as we try to make a a subtype with fewer fields
than the super).

1 files changed, 18 insertions, 0 deletions

diff --git a/test/lit/passes/signature-refining.wast b/test/lit/passes/signature-refining.wast
index c67e04917..19558d997 100644
--- a/test/lit/passes/signature-refining.wast
+++ b/test/lit/passes/signature-refining.wast
@@ -656,3 +656,21 @@
     )
   )
 )
+
+(module
+  ;; CHECK:      (type $A (func_subtype (param i32) func))
+  (type $A (func_subtype (param i32) func))
+  ;; CHECK:      (type $B (func_subtype (param i32) $A))
+  (type $B (func_subtype (param i32) $A))
+
+  ;; CHECK:      (func $bar (type $B) (param $x i32)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $bar (type $B) (param $x i32)
+   ;; The parameter to this function can be pruned. But while doing so we must
+   ;; properly preserve the subtyping of $B from $A, which means we cannot just
+   ;; remove it - we'd need to remove it from $A as well, which we don't
+   ;; attempt to do in the pass atm. So we do not optimize here.
+    (nop)
+  )
+)