Go: make //go:gen not clear by default, and clean on --force

go/gen.py

@@ -2,8 +2,18 @@ import sys
 import pathlib
 import subprocess
 import os
+import argparse
+import shutil
 from python.runfiles import runfiles
 
+def options():
+    p = argparse.ArgumentParser(description="Update generated checked in files in the Go pack")
+    p.add_argument("--force", "-f", action="store_true", help="Regenerate all files from scratch rather than updating them")
+    p.add_argument("generators", nargs=3)
+    return p.parse_args()
+
+opts = options()
+
 try:
     workspace_dir = pathlib.Path(os.environ['BUILD_WORKSPACE_DIRECTORY'])
 except KeyError:
@@ -13,20 +23,34 @@ except KeyError:
 go_extractor_dir = workspace_dir / "go" / "extractor"
 go_dbscheme = workspace_dir / "go" / "ql" / "lib" / "go.dbscheme"
 r = runfiles.Create()
-go, gazelle, go_gen_dbscheme = map(r.Rlocation, sys.argv[1:])
+go, gazelle, go_gen_dbscheme = map(r.Rlocation, opts.generators)
 
-print("updating vendor")
+
+if opts.force:
+    print("clearing vendor directory")
+    shutil.rmtree(go_extractor_dir / "vendor")
+
+existing_build_files = set(go_extractor_dir.glob("*/**/BUILD.bazel"))
+
+print("updating vendor directory")
 subprocess.check_call([go, "-C", go_extractor_dir, "work", "vendor"])
 
-print("clearing generated BUILD files")
-for build_file in go_extractor_dir.glob("*/**/BUILD.bazel"):
-    build_file.unlink()
+if opts.force:
+    print("clearing generated BUILD files")
+    for build_file in existing_build_files:
+        build_file.unlink()
 
 print("running gazelle")
 subprocess.check_call([gazelle])
 
+build_files_to_update = set(go_extractor_dir.glob("*/**/BUILD.bazel"))
+if not opts.force:
+    build_files_to_update -= existing_build_files
+    # these are always refreshed
+    build_files_to_update.update(go_extractor_dir.glob("vendor/**/BUILD.bazel"))
+
 print("adding header to generated BUILD files")
-for build_file in go_extractor_dir.glob("*/**/BUILD.bazel"):
+for build_file in build_files_to_update:
     contents = build_file.read_text()
     build_file.write_text(f"# generated running `bazel run //go/gazelle`, do not edit\n\n{contents}")