[rearchitecture] Handle cases when target is not in zip. (#3973)

We should be able to handle cases when all fuzzers in a build are
renamed.

Author: jonathanmetzman

src/clusterfuzz/_internal/bot/tasks/utasks/fuzz_task.py

@@ -83,6 +83,10 @@ class FuzzTaskError(Exception):
   """Fuzz task exception."""
 
 
+class FuzzTargetNotFoundError(Exception):
+  """Fuzz target not in build."""
+
+
 class FuzzErrorCode:
   FUZZER_TIMEOUT = -1
   FUZZER_SETUP_FAILED = -2
@@ -1282,6 +1286,8 @@ def run_engine_fuzzer(engine_impl, target_name, sync_corpus_directory,
 
   build_dir = environment.get_value('BUILD_DIR')
   target_path = engine_common.find_fuzzer_path(build_dir, target_name)
+  if target_path is None:
+    raise FuzzTargetNotFoundError(f'{target_path} is not found.')
   options = engine_impl.prepare(sync_corpus_directory, target_path, build_dir)
 
   fuzz_test_timeout = environment.get_value('FUZZ_TEST_TIMEOUT')
@@ -1543,7 +1549,7 @@ def do_engine_fuzzing(self, engine_impl):
     """Run fuzzing engine."""
     fuzz_target_name = environment.get_value('FUZZ_TARGET')
     if not fuzz_target_name:
-      raise FuzzTaskError('No fuzz targets found.')
+      raise FuzzTaskError('No fuzz targets set.')
     environment.set_value('FUZZER_NAME',
                           self.fuzz_target.fully_qualified_name())
 
@@ -1564,9 +1570,19 @@ def do_engine_fuzzing(self, engine_impl):
     # Do the actual fuzzing.
     for fuzzing_round in range(environment.get_value('MAX_TESTCASES', 1)):
       logs.log(f'Fuzzing round {fuzzing_round}.')
-      result, current_fuzzer_metadata, fuzzing_strategies = run_engine_fuzzer(
-          engine_impl, self.fuzz_target.binary, sync_corpus_directory,
-          self.testcase_directory)
+      try:
+        result, current_fuzzer_metadata, fuzzing_strategies = run_engine_fuzzer(
+            engine_impl, self.fuzz_target.binary, sync_corpus_directory,
+            self.testcase_directory)
+      except FuzzTargetNotFoundError:
+        # Ocassionally fuzz targets are deleted. This is pretty rare. Since
+        # ClusterFuzz did nothing wrong, don't bubble up an exception, consider
+        # it as we fuzzed and nothing happened so that new targets can be
+        # recorded and hopefully fuzzed instead. The old targets will eventually
+        # be garbage collected. Log this as an error to keep an eye on it.
+        logs.log_error(f'{self.fuzz_target.binary} is not in the build.')
+        return [], {}
+
       fuzzer_metadata.update(current_fuzzer_metadata)
 
       # Prepare stats.