Fix version bump baseline detection

.github/bump_version.py

@@ -1,11 +1,21 @@
 """Infer semver bump from towncrier fragment types and update version."""
 
 import re
+import subprocess
 import sys
 from pathlib import Path
 
+SEMVER_PATTERN = re.compile(r"^(\d+)\.(\d+)\.(\d+)$")
 
-def get_current_version(pyproject_path: Path) -> str:
+
+def parse_version(version: str) -> tuple[int, int, int]:
+    match = SEMVER_PATTERN.match(version)
+    if not match:
+        raise ValueError(f"Invalid semver: {version}")
+    return tuple(int(part) for part in match.groups())
+
+
+def get_pyproject_version(pyproject_path: Path) -> str:
     text = pyproject_path.read_text()
     match = re.search(r'^version\s*=\s*"(\d+\.\d+\.\d+)"', text, re.MULTILINE)
     if not match:
@@ -17,6 +27,45 @@ def get_current_version(pyproject_path: Path) -> str:
     return match.group(1)
 
 
+def get_changelog_versions(changelog_path: Path) -> list[str]:
+    if not changelog_path.exists():
+        return []
+    return re.findall(
+        r"^## \[(\d+\.\d+\.\d+)\]", changelog_path.read_text(), re.MULTILINE
+    )
+
+
+def get_git_tag_versions(repo_root: Path) -> list[str]:
+    try:
+        result = subprocess.run(
+            ["git", "tag"],
+            cwd=repo_root,
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+    except (FileNotFoundError, subprocess.CalledProcessError):
+        return []
+
+    versions = []
+    for tag in result.stdout.splitlines():
+        normalized = tag.removeprefix("v").strip()
+        if SEMVER_PATTERN.match(normalized):
+            versions.append(normalized)
+    return versions
+
+
+def get_current_version(
+    pyproject_path: Path,
+    changelog_path: Path,
+    repo_root: Path,
+) -> str:
+    candidates = [get_pyproject_version(pyproject_path)]
+    candidates.extend(get_changelog_versions(changelog_path))
+    candidates.extend(get_git_tag_versions(repo_root))
+    return max(candidates, key=parse_version)
+
+
 def infer_bump(changelog_dir: Path) -> str:
     fragments = [
         f for f in changelog_dir.iterdir() if f.is_file() and f.name != ".gitkeep"
@@ -48,12 +97,20 @@ def bump_version(version: str, bump: str) -> str:
         return f"{major}.{minor}.{patch + 1}"
 
 
-def update_file(path: Path, old_version: str, new_version: str):
+def update_file(path: Path, new_version: str):
     text = path.read_text()
-    updated = text.replace(
-        f'version = "{old_version}"',
-        f'version = "{new_version}"',
+    updated, replacements = re.subn(
+        r'(^version\s*=\s*")(\d+\.\d+\.\d+)(")',
+        rf"\g<1>{new_version}\g<3>",
+        text,
+        flags=re.MULTILINE,
     )
+    if replacements == 0:
+        print(
+            f"Could not update version in {path}",
+            file=sys.stderr,
+        )
+        sys.exit(1)
     if updated != text:
         path.write_text(updated)
         print(f"  Updated {path}")
@@ -62,15 +119,16 @@ def update_file(path: Path, old_version: str, new_version: str):
 def main():
     root = Path(__file__).resolve().parent.parent
     pyproject = root / "pyproject.toml"
+    changelog = root / "CHANGELOG.md"
     changelog_dir = root / "changelog.d"
 
-    current = get_current_version(pyproject)
+    current = get_current_version(pyproject, changelog, root)
     bump = infer_bump(changelog_dir)
     new = bump_version(current, bump)
 
     print(f"Version: {current} -> {new} ({bump})")
 
-    update_file(pyproject, current, new)
+    update_file(pyproject, new)
 
 
 if __name__ == "__main__":

.github/workflows/push.yaml

@@ -108,6 +108,9 @@ jobs:
         uses: actions/checkout@v4
         with:
           token: ${{ steps.app-token.outputs.token }}
+          fetch-depth: 0
+      - name: Fetch tags
+        run: git fetch --tags --force
       - name: Setup Python
         uses: actions/setup-python@v5
         with:

changelog.d/versioning-highest-release.fixed.md

@@ -0,0 +1 @@
+Fix the release versioning workflow so it bumps from the highest known released version instead of regressing to a stale version from `pyproject.toml`.

tests/test_bump_version.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+MODULE_PATH = REPO_ROOT / ".github" / "bump_version.py"
+
+spec = importlib.util.spec_from_file_location("bump_version", MODULE_PATH)
+bump_version = importlib.util.module_from_spec(spec)
+assert spec.loader is not None
+spec.loader.exec_module(bump_version)
+
+
+def test_get_current_version_prefers_highest_seen_version(tmp_path):
+    pyproject = tmp_path / "pyproject.toml"
+    pyproject.write_text('[project]\nversion = "3.4.1"\n')
+    changelog = tmp_path / "CHANGELOG.md"
+    changelog.write_text(
+        "## [3.4.1] - 2026-04-13\n\n"
+        "### Changed\n\n"
+        "- Current change.\n\n"
+        "## [3.4.2] - 2026-04-12\n\n"
+        "### Changed\n\n"
+        "- Prior release.\n"
+    )
+
+    current = bump_version.get_current_version(pyproject, changelog, tmp_path)
+
+    assert current == "3.4.2"
+
+
+def test_get_current_version_uses_git_tags_when_available(tmp_path, monkeypatch):
+    pyproject = tmp_path / "pyproject.toml"
+    pyproject.write_text('[project]\nversion = "3.4.1"\n')
+    changelog = tmp_path / "CHANGELOG.md"
+    changelog.write_text("## [3.4.1] - 2026-04-13\n")
+
+    monkeypatch.setattr(
+        bump_version,
+        "get_git_tag_versions",
+        lambda _repo_root: ["3.4.3"],
+    )
+
+    current = bump_version.get_current_version(pyproject, changelog, tmp_path)
+
+    assert current == "3.4.3"
+
+
+def test_update_file_replaces_stale_version_field(tmp_path):
+    pyproject = tmp_path / "pyproject.toml"
+    pyproject.write_text('[project]\nversion = "3.4.1"\n')
+
+    bump_version.update_file(pyproject, "3.4.3")
+
+    assert 'version = "3.4.3"' in pyproject.read_text()