build: default to incremental build

Bug: http://b/300494075

Post-submit builds are no longer incremental, so default to an
incremental build but print contents of OUT_DIR for debugging purposes.

Test: build.py locally and presubmit

Change-Id: I08d17096386d4bba372735cd798cd48757e73967

2 files changed, 5 insertions, 3 deletions

diff --git a/do_build.py b/do_build.py
index 8408d47..bb9a63a 100755
--- a/do_build.py
+++ b/do_build.py
@@ -944,12 +944,12 @@ def parse_args():
     incremental_group.add_argument(
         '--incremental',
         action='store_true',
-        default=False,
+        default=True,
         help='Keep paths.OUT_DIR if it exists')
     incremental_group.add_argument(
         '--no-incremental',
         action='store_false',
-        default=False,
+        default=True,
         dest='incremental',
         help='Delete paths.OUT_DIR if it exists (default)')
 
@@ -965,7 +965,8 @@ def main():
             logger().info(f'Removing {paths.OUT_DIR}')
             utils.clean_out_dir()
         else:
-            logger().info(f'Keeping older build in {paths.OUT_DIR}')
+            out_dir_items = ' '.join(map(str, paths.OUT_DIR.iterdir()))
+            logger().info(f'Keeping older build in {paths.OUT_DIR}: {out_dir_items}')
 
     timer.Timer.register_atexit(paths.DIST_DIR / 'build_times.txt')
 
diff --git a/utils.py b/utils.py
index da0d427..ea3993c 100644
--- a/utils.py
+++ b/utils.py
@@ -155,6 +155,7 @@ def clean_out_dir():
     for child in paths.OUT_DIR.iterdir():
         if child.name == 'prebuilt_cached':
             continue
+        logger().info(f'removing {child} in {paths.OUT_DIR}')
         if child.is_dir():
             shutil.rmtree(child)
         else: