fix(changelog): fix merge_prerelease flag not working if changelog contains only prereleases

Author: zimmermannJakob

commitizen/changelog_formats/base.py

@@ -80,7 +80,9 @@ def get_latest_full_release(self, filepath: str) -> IncrementalMergeInfo:
             return self.get_latest_full_release_from_file(changelog_file)
 
     def get_latest_full_release_from_file(self, file: IO[Any]) -> IncrementalMergeInfo:
+        latest_version_index: int | None = None
         for index, line in enumerate(file):
+            latest_version_index = index
             line = line.strip().lower()
 
             parsed = self.parse_version_from_title(line)
@@ -89,7 +91,7 @@ def get_latest_full_release_from_file(self, file: IO[Any]) -> IncrementalMergeIn
                     GitTag(parsed.tag, "", "")
                 ).is_prerelease:
                     return IncrementalMergeInfo(name=parsed.tag, index=index)
-        return IncrementalMergeInfo()
+        return IncrementalMergeInfo(index=latest_version_index)
 
     def parse_version_from_title(self, line: str) -> VersionTag | None:
         """

commitizen/commands/changelog.py

@@ -225,12 +225,17 @@ def __call__(self) -> None:
             latest_full_release_info = self.changelog_format.get_latest_full_release(
                 self.file_name
             )
-            start_rev = latest_full_release_info.name or ""
             if latest_full_release_info.index:
                 changelog_meta.unreleased_start = 0
                 changelog_meta.latest_version_position = latest_full_release_info.index
                 changelog_meta.unreleased_end = latest_full_release_info.index - 1
 
+            start_rev = latest_full_release_info.name or ""
+            if not start_rev and latest_full_release_info.index:
+                # Only pre-releases in changelog
+                changelog_meta.latest_version_position = None
+                changelog_meta.unreleased_end = latest_full_release_info.index + 1
+
         commits = git.get_commits(start=start_rev, end=end_rev, args="--topo-order")
         if not commits and (
             self.current_version is None or not self.current_version.is_prerelease