Fuzzer: Fix a missing return of a trap (#4485)

We emitted the right text to stdout to indicate a trap in one code path, but did
not return a Trap from the function. As a result, we'd continue and hit the
assert on the next line.

2 files changed, 15 insertions, 0 deletions

diff --git a/src/tools/execution-results.h b/src/tools/execution-results.h
index 94447ab4d..78972cfc9 100644
--- a/src/tools/execution-results.h
+++ b/src/tools/execution-results.h
@@ -250,6 +250,7 @@ struct ExecutionResults {
         if (!param.isDefaultable()) {
           std::cout << "[trap fuzzer can only send defaultable parameters to "
                        "exports]\n";
+          return Trap{};
         }
         arguments.push_back(Literal::makeZero(param));
       }
diff --git a/test/lit/exec/non-nullable.wast b/test/lit/exec/non-nullable.wast
new file mode 100644
index 000000000..d443947c6
--- /dev/null
+++ b/test/lit/exec/non-nullable.wast
@@ -0,0 +1,14 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --output=fuzz-exec and should not be edited.
+
+;; RUN: wasm-opt %s -all --fuzz-exec -q -o /dev/null 2>&1 | filecheck %s
+
+(module
+  ;; CHECK:      [fuzz-exec] calling get-ref
+  ;; CHECK-NEXT: [trap fuzzer can only send defaultable parameters to exports]
+  (func "get-ref" (param $0 (ref any))
+    (nop)
+  )
+)
+;; CHECK:      [fuzz-exec] calling get-ref
+;; CHECK-NEXT: [trap fuzzer can only send defaultable parameters to exports]
+;; CHECK-NEXT: [fuzz-exec] comparing get-ref