postprocess: Workaround for Python timestamp mismatch

Python mtime timestamp logic does not work well with ostree force 0
mtime.

Use a small script to post-process all compiled '.pyc' and force the
timestamp to 0.

See: ostreedev/ostree#1469

Co-Authored-By: Miro Hrončok <miro@hroncok.cz>

postprocess.sh

@@ -107,3 +107,47 @@ chmod 755 /usr/libexec/fedora-silverblue-readonly-sysroot
 
 # Enable the corresponding unit
 systemctl enable fedora-silverblue-readonly-sysroot.service
+
+###
+
+# Workaround for Python timestamp mismatch
+# See: https://github.com/ostreedev/ostree/issues/1469
+
+echo '
+import os
+import re
+
+MIN_MAGIC = 3390  # The first magic number supporting PEP 552
+ZERO = bytes((0, 0, 0, 0))
+
+def pyc_set_zero_mtime(pyc_path):
+    with open(pyc_path, "r+b") as f:
+        w = f.read(4)
+        if len(w) < 4:
+            return 0
+
+        magic = (w[0] + (w[1] << 8) + (w[2] << 16) + (w[3] << 24)) & 0xFFFF
+        if magic < MIN_MAGIC:
+            invalidation = ZERO
+        else:
+            invalidation = f.read(4)
+            if len(invalidation) < 4:
+                return 0
+
+        if invalidation == ZERO:
+            f.write(ZERO)
+            return 1
+    return 0
+
+if __name__ == "__main__":
+    REGEX = re.compile(r".*/__pycache__/[^/]+\.cpython-.*(\.opt-1|\.opt-2)?\.pyc$")
+    count = 0
+
+    for root, dirs, files in os.walk("/usr"):
+        for file in files:
+            path = os.path.join(root, file)
+            if REGEX.match(path):
+                count += pyc_set_zero_mtime(path)
+
+    print(f"Processed {count} pyc files")
+' | python