DiscogapicConfigGen: Use a temporary output directory (#669)

DiscogapicConfigGen generates gapic yaml from discovery docs, and therefore the flag gapic_yaml is used as output instead of input (which is the usual case for codegen).

When trying to refresh gapic config for compute artman creates this default artman-genfiles in my local environment while does not drop any output there. Therefore it seems clearer to just use a temporary directory to hold the generated gapic config before moving to the right place.

Also, if user specifies the output_dir flag when invoking artman generate discogapic_config, throw a command line warning saying that the flag is ignored, and output is saved in the directory given by gapic_yaml.

artman/cli/main.py

@@ -29,6 +29,7 @@
 import pprint
 import subprocess
 import sys
+import tempfile
 import traceback
 
 import pkg_resources
@@ -46,7 +47,7 @@
 VERSION = pkg_resources.get_distribution('googleapis-artman').version
 ARTMAN_DOCKER_IMAGE = 'googleapis/artman:%s' % VERSION
 RUNNING_IN_ARTMAN_DOCKER_TOKEN = 'RUNNING_IN_ARTMAN_DOCKER'
-
+DEFAULT_OUTPUT_DIR = './artman-genfiles'
 
 def main(*args):
     """Main method of artman."""
@@ -124,9 +125,9 @@ def parse_args(*args):
     parser.add_argument(
         '--output-dir',
         type=str,
-        default='./artman-genfiles',
+        default=DEFAULT_OUTPUT_DIR,
         help='[Optional] Directory to store output generated by artman. '
-        'Default to `./artman-genfiles`', )
+        'Default to `' + DEFAULT_OUTPUT_DIR + '`', )
     parser.add_argument(
         '--root-dir',
         type=str,
@@ -273,6 +274,10 @@ def normalize_flags(flags, user_config):
     elif artifact_type == Artifact.DISCOGAPIC_CONFIG:
         pipeline_name = 'DiscoGapicConfigPipeline'
         pipeline_args['discovery_doc'] = artifact_config.discovery_doc
+        if os.path.abspath(flags.output_dir) != os.path.abspath(DEFAULT_OUTPUT_DIR):
+            logger.warning("`output_dir` is ignored in DiscoGapicConfigGen. "
+             + "Yamls are saved at the path specified by `gapic_yaml`.")
+        pipeline_args['output_dir'] = tempfile.mkdtemp()
     elif artifact_type == Artifact.PROTOBUF:
         pipeline_name = 'ProtoClientPipeline'
         pipeline_args['language'] = language