Fix regression for files without permissions.

CHANGELOG.md

@@ -82,7 +82,7 @@ The versions follow [semantic versioning](https://semver.org).
 
 - Fix faulty file types:
   - Extensible Stylesheet Language (`.xsl`) actually uses HTML comment syntax
-- Allow creating .license file for write-protected files (#347)
+- Allow creating .license file for write-protected files (#347) (#418)
 - Make `download` subcommand work correctly outside of project root and with
   `--root` (#430)
 

src/reuse/header.py

@@ -15,13 +15,14 @@
 
 import datetime
 import logging
+import os
 import re
 import sys
 from argparse import ArgumentParser
 from gettext import gettext as _
 from os import PathLike
 from pathlib import Path
-from typing import List, NamedTuple, Optional, Sequence
+from typing import Iterable, List, NamedTuple, Optional, Sequence
 
 from binaryornot.check import is_binary
 from boolean.boolean import ParseError
@@ -551,6 +552,9 @@ def run(args, project: Project, out=sys.stdout) -> int:
 
     paths = [_determine_license_path(path) for path in args.path]
 
+    if not args.explicit_license:
+        _verify_write_access(paths, args.parser)
+
     # Verify line handling and comment styles before proceeding
     if args.style is None and not args.explicit_license:
         _verify_paths_line_handling(
@@ -624,3 +628,13 @@ def run(args, project: Project, out=sys.stdout) -> int:
         )
 
     return min(result, 1)
+
+
+def _verify_write_access(paths: Iterable[PathLike], parser: ArgumentParser):
+    not_writeable = [
+        str(path) for path in paths if not os.access(path, os.W_OK)
+    ]
+    if not_writeable:
+        parser.error(
+            _("can't write to '{}'").format("', '".join(not_writeable))
+        )

tests/test_main_addheader.py

@@ -724,6 +724,30 @@ def test_addheader_explicit_license_doesnt_write_to_file(
     assert simple_file.read_text() == "Preserve this"
 
 
+def test_addheader_to_read_only_file_does_not_traceback(
+    fake_repository, stringio, mock_date_today
+):
+    """Trying to add a header without having write permission, shouldn't result
+    in a traceback. See issue #398"""
+    _file = fake_repository / "test.sh"
+    _file.write_text("#!/bin/sh")
+    _file.chmod(mode=stat.S_IREAD)
+    with pytest.raises(SystemExit) as info:
+        main(
+            [
+                "addheader",
+                "--license",
+                "Apache-2.0",
+                "--copyright",
+                "mycorp",
+                "--style",
+                "python",
+                "test.sh",
+            ]
+        )
+    assert info.value  # should not exit with 0
+
+
 def test_addheader_license_file(fake_repository, stringio, mock_date_today):
     """Add a header to a .license file if it exists."""
     simple_file = fake_repository / "foo.py"