feat: Support updating changelog in-place

Issue #15: #15

src/git_changelog/cli.py

@@ -101,6 +101,43 @@ def get_parser() -> argparse.ArgumentParser:
     parser.add_argument(
         "-h", "--help", action="help", default=argparse.SUPPRESS, help="Show this help message and exit."
     )
+    parser.add_argument(
+        "-i",
+        "--in-place",
+        action="store_true",
+        dest="in_place",
+        default=False,
+        help="Insert new entries (versions missing from changelog) in-place. "
+        "An output file must be specified. With custom templates, "
+        "you must pass two additional arguments: --version-regex and --marker-line. "
+        "When writing in-place, an 'inplace' variable "
+        "will be injected in the Jinja context, "
+        "allowing to adapt the generated contents "
+        "(for example to skip changelog headers or footers).",
+    )
+    parser.add_argument(
+        "-g",
+        "--version-regex",
+        action="store",
+        dest="version_regex",
+        default=None,
+        help="A regular expression to match versions in the existing changelog "
+        "(used to find the latest release) when writing in-place. "
+        "The regular expression must be a Python regex with a 'version' named group. ",
+    )
+
+    parser.add_argument(
+        "-m",
+        "--marker-line",
+        action="store",
+        dest="marker_line",
+        default=None,
+        help="A marker line at which to insert new entries "
+        "(versions missing from changelog). "
+        "If two marker lines are present in the changelog, "
+        "the contents between those two lines will be overwritten "
+        "(useful to update an 'Unreleased' entry for example).",
+    )
     parser.add_argument(
         "-o",
         "--output",
@@ -160,6 +197,21 @@ def get_parser() -> argparse.ArgumentParser:
     return parser
 
 
+def _latest(lines: list[str], regex: Pattern) -> str | None:
+    for line in lines:
+        match = regex.search(line)
+        if match:
+            return match.groupdict()["version"]
+    return None
+
+
+def _unreleased(versions: list[Version], last_release: str):
+    for index, version in enumerate(versions):
+        if version.tag == last_release:
+            return versions[:index]
+    return versions
+
+
 def main(args: list[str] | None = None) -> int:
     """
     Run the main program.

tests/test_end_to_end.py

@@ -95,3 +95,32 @@ def test_rendering_custom_sections(repo):
         if section_type != "feat":
             assert section_title not in rendered
 
+
+def test_rendering_in_place(repo):  # noqa: WPS218
+    """Render changelog in-place.
+
+    Parameters:
+        repo: Path to a temporary repository.
+    """
+    _, rendered = build_and_render(
+        str(repo),
+        style="angular",
+        bump_latest=False,
+        output=repo.joinpath("changelog.md").as_posix(),
+        template="keepachangelog",
+    )
+    assert len(re.findall("<!-- insertion marker -->", rendered)) == 2
+    assert "Unreleased" in rendered
+    latest_tag = "91.6.14"
+    assert latest_tag not in rendered
+    _git("-C", repo, "tag", latest_tag)
+    _, rendered = build_and_render(
+        str(repo),
+        style="angular",
+        bump_latest=True,
+        output=repo.joinpath("changelog.md").as_posix(),
+        template="keepachangelog",
+    )
+    assert len(re.findall("<!-- insertion marker -->", rendered)) == 1
+    assert "Unreleased" not in rendered
+    assert latest_tag in rendered