1 files changed, 31 insertions, 7 deletions
diff --git a/scripts/set_versions.py b/scripts/set_versions.py
index 3bd2ab4..de90693 100644
--- a/scripts/set_versions.py
+++ b/scripts/set_versions.py
@@ -1,12 +1,24 @@
-"""Generate a Dockerfile from in.Dockerfile and a version JSON file, and write version info."""
+"""
+Generate a Dockerfile from in.Dockerfile and a version JSON file, and write version info.
 
+If the argument --error-modified is passed, the script will not write any output
+and will exit with status code 1 if the output files were modified.
+"""
+
+import difflib
+import sys
 from pathlib import Path
 from textwrap import dedent
 
-from scripts.python_version import ALL_VERSIONS, MAIN_VERSION
+try:
+    from scripts.python_version import ALL_VERSIONS, MAIN_VERSION
+except ModuleNotFoundError:
+    sys.path.insert(0, Path(__file__).parent.parent.absolute().as_posix())
+    from scripts.python_version import ALL_VERSIONS, MAIN_VERSION
 
 DOCKERFILE_TEMPLATE = Path("scripts/in.Dockerfile").read_text("utf-8")
 DOCKERFILE = Path("Dockerfile")
+ERROR_MODIFIED = "--error-modified" in sys.argv
 
 # Download and copy multiple python images into one layer
 python_build = ""
@@ -32,12 +44,24 @@ for version in ALL_VERSIONS:
 python_build = f"FROM python:{MAIN_VERSION.image_tag} as base-first\n" + python_build
 
 # Write new dockerfile
-DOCKERFILE.write_text(
+# fmt: off
+# Black makes the following block much less readable
+dockerfile_out = (
     "# THIS FILE IS AUTOGENERATED, DO NOT MODIFY! #\n"
-    + DOCKERFILE_TEMPLATE.replace("{python_install_commands}", python_build)
-    .replace("{final_base}", previous_layer)
-    .replace("{main_version_tag}", MAIN_VERSION.image_tag),
-    "utf-8",
+    + DOCKERFILE_TEMPLATE
+    .replace("{python_install_commands}", python_build)
+    .replace("{final_base}", previous_layer).replace("{main_version_tag}", MAIN_VERSION.image_tag)
 )
+# fmt: on
+
+if ERROR_MODIFIED:
+    if (original := DOCKERFILE.read_text("utf-8")) != dockerfile_out:
+        print("Dockerfile modified:")
+        print("\n".join(difflib.unified_diff(dockerfile_out.splitlines(), original.splitlines())))
+        raise SystemExit(1)
+    else:
+        exit(0)
+else:
+    DOCKERFILE.write_text(dockerfile_out, "utf-8")
 
 print("Finished!")