feat: check headers of files imported from Apache repos (#14)

## What's Changed

adbc-drivers/bigquery#43 (comment)

Closes #13.

Author: lidavidm

.rat-apache

@@ -0,0 +1,16 @@
+# Copyright (c) 2025 ADBC Drivers Contributors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+.github/workflows/dev_issues.yaml
+adbc_drivers_dev/title_check.py

adbc_drivers_dev/rat/cli.py

@@ -15,7 +15,9 @@
 import argparse
 import fnmatch
 import io
+import re
 import subprocess
+import tarfile
 import tempfile
 import xml.etree.ElementTree as ET
 from pathlib import Path
@@ -81,6 +83,18 @@ def main():
                 if line and not line.startswith("#"):
                     exclusions.append(line)
 
+    # ------------------------------------------------------------
+    # Load the file listing files imported from Apache repos
+    # ------------------------------------------------------------
+    apache_file = root / ".rat-apache"
+    needs_apache_header = set()
+    if apache_file.is_file():
+        with apache_file.open("r") as f:
+            for line in f:
+                line = line.strip()
+                if line and not line.startswith("#"):
+                    needs_apache_header.add(line)
+
     with tempfile.TemporaryDirectory() as scratch:
         scratch = Path(scratch).resolve()
         archive = scratch / "rat.tar"
@@ -122,4 +136,61 @@ def main():
             unapproved += 1
             print("-", filename)
 
+        missing_copyright = []
+        missing_apache_header = []
+        should_not_have_apache_header = []
+        copyright_re = re.compile(r"Copyright \(c\) [0-9]{4} ADBC Drivers Contributors")
+        header_re = re.compile(
+            r"This file has been modified from its original version, which is under the Apache License: Licensed to the Apache Software Foundation"
+        )
+        sep_re = re.compile(r"[^a-zA-Z0-9,:()]+")
+        with tarfile.open(archive, "r") as tar:
+            for member in tar.getmembers():
+                if not member.isfile():
+                    continue
+
+                with tar.extractfile(member) as f:
+                    lines = []
+                    for _ in range(20):
+                        lines.append(f.readline())
+
+                content = b" ".join(lines).decode("utf-8")
+                content = sep_re.sub(" ", content)
+
+                if not copyright_re.search(content):
+                    if (
+                        not member.name.endswith("LICENSE.txt")
+                        and not member.name.endswith("NOTICE.txt")
+                        and not any(
+                            fnmatch.fnmatch(member.name, exclusion)
+                            for exclusion in exclusions
+                        )
+                    ):
+                        missing_copyright.append(member.name)
+
+                if member.name in needs_apache_header:
+                    if not header_re.search(content):
+                        missing_apache_header.append(member.name)
+                elif header_re.search(content):
+                    should_not_have_apache_header.append(member.name)
+
+        if missing_copyright:
+            print("Files missing ADBC Drivers Contributors copyright header:")
+            for name in missing_copyright:
+                print("-", name)
+
+        if missing_apache_header:
+            print("Files missing 'This file has been modified' header:")
+            for name in missing_apache_header:
+                print("-", name)
+
+        if should_not_have_apache_header:
+            print("Files that should not have 'This file has been modified' header:")
+            for name in should_not_have_apache_header:
+                print("-", name)
+
+        unapproved += len(missing_copyright)
+        unapproved += len(missing_apache_header)
+        unapproved += len(should_not_have_apache_header)
+
     return unapproved