gen_compile_commands: make -o option independent of -d option

Change the -o option independent of the -d option, which is I think
clearer behavior. Some people may like to use -d to specify a separate
output directory, but still output the compile_commands.py in the
source directory (unless the source tree is read-only) because it is
the default location Clang Tools search for the compilation database.

Also, move the default parameter to the default= argument of the
.add_argument().
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/gen_compile_commands.py

@@ -39,11 +39,13 @@ def parse_arguments():
 
     directory_help = ('specify the output directory used for the kernel build '
                       '(defaults to the working directory)')
-    parser.add_argument('-d', '--directory', type=str, help=directory_help)
+    parser.add_argument('-d', '--directory', type=str, default='.',
+                        help=directory_help)
 
-    output_help = ('The location to write compile_commands.json (defaults to '
-                   'compile_commands.json in the search directory)')
-    parser.add_argument('-o', '--output', type=str, help=output_help)
+    output_help = ('path to the output command database (defaults to ' +
+                   _DEFAULT_OUTPUT + ')')
+    parser.add_argument('-o', '--output', type=str, default=_DEFAULT_OUTPUT,
+                        help=output_help)
 
     log_level_help = ('the level of log messages to produce (defaults to ' +
                       _DEFAULT_LOG_LEVEL + ')')
@@ -52,11 +54,9 @@ def parse_arguments():
 
     args = parser.parse_args()
 
-    directory = args.directory or os.getcwd()
-    output = args.output or os.path.join(directory, _DEFAULT_OUTPUT)
-    directory = os.path.abspath(directory)
-
-    return args.log_level, directory, output
+    return (args.log_level,
+            os.path.abspath(args.directory),
+            args.output)
 
 
 def process_line(root_directory, command_prefix, file_path):