Handle deletion of uncommitted news fragments

Before this commit, all the news fragments needed to be committed into
git, or the fragments removal after building the news file would crash.

In my workflow, I add missing fragments before building the news file
because I'm extracting author names from the git log, and towncrier
crashes at the end of the build process.

Signed-off-by: Aurélien Bompard <aurelien@bompard.org>

src/towncrier/_git.py

@@ -4,21 +4,50 @@
 from __future__ import annotations
 
 import os
+import sys
 
-from subprocess import STDOUT, call, check_output
+from subprocess import STDOUT, CalledProcessError, call, check_output
+
+
+def run(args, **kwargs):
+    """Run a command.
+
+    Use UTF-8 both when sys.stdout does not have .encoding (Python 2.7) and
+    when the attribute is present but set to None (explicitly piped output
+    and also some CI such as GitHub Actions).
+    """
+    output = check_output(args, **kwargs)
+    if not isinstance(output, str):
+        encoding = getattr(sys.stdout, "encoding", None)
+        if encoding is None:
+            encoding = "utf8"
+        output = output.decode(encoding)
+    return output.strip()
 
 
 def remove_files(fragment_filenames: list[str]) -> None:
-    if fragment_filenames:
-        call(["git", "rm", "--quiet"] + fragment_filenames)
+    if not fragment_filenames:
+        return
+
+    # Filter out files that are unknown to git
+    try:
+        git_fragments = run(["git", "ls-files"] + fragment_filenames).split("\n")
+        git_fragments = [os.path.abspath(f) for f in git_fragments]
+    except CalledProcessError:
+        git_fragments = []
+
+    call(["git", "rm", "--quiet", "--force"] + git_fragments)
+    unknown_fragments = set(fragment_filenames) - set(git_fragments)
+    for unknown_fragment in unknown_fragments:
+        os.remove(unknown_fragment)
 
 
 def stage_newsfile(directory: str, filename: str) -> None:
     call(["git", "add", os.path.join(directory, filename)])
 
 
 def get_remote_branches(base_directory: str) -> list[str]:
-    output = check_output(
+    output = run(
         ["git", "branch", "-r"], cwd=base_directory, encoding="utf-8", stderr=STDOUT
     )
 
@@ -28,7 +57,7 @@ def get_remote_branches(base_directory: str) -> list[str]:
 def list_changed_files_compared_to_branch(
     base_directory: str, compare_with: str
 ) -> list[str]:
-    output = check_output(
+    output = run(
         ["git", "diff", "--name-only", compare_with + "..."],
         cwd=base_directory,
         encoding="utf-8",

src/towncrier/newsfragments/357.feature.rst

@@ -0,0 +1 @@
+It can now handle news fragments which are not part of the git repository. For example uncommited or unstagged files.

src/towncrier/test/test_build.py

@@ -6,6 +6,7 @@
 
 from datetime import date
 from pathlib import Path
+from subprocess import call
 from textwrap import dedent
 from unittest.mock import patch
 
@@ -747,8 +748,8 @@ def do_build_once_with(version, fragment_file, fragment):
                     "--yes",
                 ],
             )
-            # not git repository, manually remove fragment file
-            Path(f"newsfragments/{fragment_file}").unlink()
+            # fragment files unknown to git are removed even without a git repo
+            # Path(f"newsfragments/{fragment_file}").unlink()
             return result
 
         results = []
@@ -845,8 +846,8 @@ def do_build_once_with(version, fragment_file, fragment):
                 ],
                 catch_exceptions=False,
             )
-            # not git repository, manually remove fragment file
-            Path(f"newsfragments/{fragment_file}").unlink()
+            # fragment files unknown to git are removed even without a git repo
+            # Path(f"newsfragments/{fragment_file}").unlink()
             return result
 
         results = []
@@ -1530,3 +1531,55 @@ def test_orphans_in_non_showcontent_markdown(self, runner):
 
         self.assertEqual(0, result.exit_code, result.output)
         self.assertEqual(expected_output, result.output)
+
+    @with_git_project()
+    def test_uncommitted_files(self, runner, commit):
+        """
+        At build time, it will delete any fragment file regardless of its stage,
+        included files that are not part of the git reporsitory,
+        or are just staged or modified.
+        """
+        # 123 is committed, 124 is modified, 125 is just added, 126 is unknown
+
+        with open("foo/newsfragments/123.feature", "w") as f:
+            f.write("Adds levitation")
+        with open("foo/newsfragments/124.feature", "w") as f:
+            f.write("Extends levitation")
+
+        commit()
+
+        with open("foo/newsfragments/125.feature", "w") as f:
+            f.write("Baz levitation")
+        with open("foo/newsfragments/126.feature", "w") as f:
+            f.write("Fix (literal) crash")
+
+        with open("foo/newsfragments/124.feature", "a") as f:
+            f.write(" for an hour")
+        call(["git", "add", "foo/newsfragments/125.feature"])
+
+        result = runner.invoke(_main, ["--date", "01-01-2001", "--yes"])
+
+        self.assertEqual(0, result.exit_code)
+        for fragment in ("123", "124", "125", "126"):
+            self.assertFalse(os.path.isfile(f"foo/newsfragments/{fragment}.feature"))
+
+        path = "NEWS.rst"
+        self.assertTrue(os.path.isfile(path))
+        news_contents = open(path).read()
+        self.assertEqual(
+            news_contents,
+            dedent(
+                """\
+                Foo 1.2.3 (01-01-2001)
+                ======================
+
+                Features
+                --------
+
+                - Adds levitation (#123)
+                - Extends levitation for an hour (#124)
+                - Baz levitation (#125)
+                - Fix (literal) crash (#126)
+                """
+            ),
+        )