Do not consider missing command as internal failure.

client/run_isolated.py

 #!/usr/bin/env python
 # Copyright 2012 The Swarming Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0 that
 # can be found in the LICENSE file.
 
 """Reads a .isolated, creates a tree of hardlinks and runs the test.
 
 To improve performance, it keeps a local cache. The local cache can safely be
 deleted.
 
@@ skipping 177 matching lines @@
             #   hard_timed_out will be set but the process exit code will be
             #   script provided.
             # - processed exited late, exit code will be -9 on posix.
             logging.warning('Grace exhausted; sending SIGKILL')
             proc.kill()
       logging.info('Waiting for proces exit')
       exit_code = proc.wait()
     except OSError:
       # This is not considered to be an internal error. The executable simply
       # does not exit.
+      sys.stderr.write(
+          '<The executable does not exist or a dependent library is missing>\n'
+          '<Check for missing .so/.dll in the .isolate or GN file>\n'
+          '<Command: %s>\n' % command)
+      if os.environ.get('SWARMING_TASK_ID'):
+        # Give an additional hint when running as a swarming task.
+        sys.stderr.write(
+            '<See the task\'s page for commands to help diagnose this issue '
+            'by reproducing the task locally>\n')
       exit_code = 1
   logging.info(
       'Command finished with exit code %d (%s)',
       exit_code, hex(0xffffffff & exit_code))
   return exit_code, had_hard_timeout
 
 
 def delete_and_upload(storage, out_dir, leak_temp_dir):
   """Deletes the temporary run directory and uploads results back.
 
@@ skipping 56 matching lines @@
     if not fs.isdir(root_dir):
       fs.makedirs(root_dir, 0700)
     prefix = u''
   else:
     root_dir = os.path.dirname(cache.cache_dir) if cache.cache_dir else None
     prefix = u'isolated_'
   run_dir = make_temp_dir(prefix + u'run', root_dir)
   out_dir = make_temp_dir(prefix + u'out', root_dir)
   tmp_dir = make_temp_dir(prefix + u'tmp', root_dir)
   try:
-    bundle = isolateserver.fetch_isolated(
-        isolated_hash=isolated_hash,
-        storage=storage,
-        cache=cache,
-        outdir=run_dir,
-        require_command=True)
+    try:
+      bundle = isolateserver.fetch_isolated(
+          isolated_hash=isolated_hash,
+          storage=storage,
+          cache=cache,
+          outdir=run_dir,
+          require_command=True)
+    except isolateserver.IsolatedErrorNoCommand:
+      # Handle this as a task failure, not an internal failure.
+      sys.stderr.write(
+          '<The .isolated doesn\'t declare any command to run!>\n'
+          '<Check your .isolate for missing \'command\' variable>\n')
+      if os.environ.get('SWARMING_TASK_ID'):
+        # Give an additional hint when running as a swarming task.
+        sys.stderr.write('<This occurs at the \'isolate\' step>\n')
+      result['exit_code'] = 1
+      return result
 
     change_tree_read_only(run_dir, bundle.read_only)
     cwd = os.path.normpath(os.path.join(run_dir, bundle.relative_cwd))
     command = bundle.command + extra_args
     file_path.ensure_command_has_abs_path(command, cwd)
     result['exit_code'], result['had_hard_timeout'] = run_command(
         process_command(command, out_dir), cwd, tmp_dir, hard_timeout,
         grace_period)
   except Exception as e:
     # An internal error occured. Report accordingly so the swarming task will be
@@ skipping 180 matching lines @@
     assert storage.hash_algo == cache.hash_algo
     return run_tha_test(
         options.isolated, storage, cache, options.leak_temp_dir, options.json,
         options.root_dir, options.hard_timeout, options.grace_period, args)
 
 
 if __name__ == '__main__':
   # Ensure that we are always running with the correct encoding.
   fix_encoding.fix_encoding()
   sys.exit(main(sys.argv[1:]))