Fuzzer: Show a clear error if a given wasm fails to run (#4672)

Without this the error from a bad given wasm file - either by the user, or during
a reduction where smaller wasms are given - could be very confusing. A bad
given wasm file during reduction, in particular, indicates a bug in the reducer
most likely.

1 files changed, 5 insertions, 1 deletions

diff --git a/scripts/fuzz_opt.py b/scripts/fuzz_opt.py
index 696ccc4bd..8ef4df334 100755
--- a/scripts/fuzz_opt.py
+++ b/scripts/fuzz_opt.py
@@ -1048,7 +1048,11 @@ def test_one(random_input, given_wasm):
         # apply properties like not having any NaNs, which the original fuzz
         # wasm had applied. that is, we need to preserve properties like not
         # having nans through reduction.
-        run([in_bin('wasm-opt'), given_wasm, '-o', 'a.wasm'] + FUZZ_OPTS + FEATURE_OPTS)
+        try:
+            run([in_bin('wasm-opt'), given_wasm, '-o', 'a.wasm'] + FUZZ_OPTS + FEATURE_OPTS)
+        except Exception as e:
+            print("Internal error in fuzzer! Could not run given wasm")
+            raise e
     else:
         # emit the target features section so that reduction can work later,
         # without needing to specify the features