fix(changelog): add changelog_subject_only to skip body parsing

Closes #1267.

`generate_tree_from_commits()` historically parses the commit subject and
each `\n\n`-separated body block against `commit_parser`, so a commit
whose subject is `feat: ...` and whose body contains another
`refactor: ...` line produces two changelog entries instead of one.
Maintainer ack on #1267 confirms this is undesirable, but changing the
default is a behavioural break.

This change introduces `changelog_subject_only` (default `false`) on
`Settings`. When set to `true`, the body iteration in
`generate_tree_from_commits()` is skipped, leaving only the subject
line to be matched. The setting is plumbed through
`commands/changelog.py` so both `cz changelog` and `cz bump --changelog`
honour it.

A regression test exercises both modes against a commit whose body
contains a parser-matching block.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bearomorphism

commitizen/changelog.py

@@ -100,6 +100,7 @@ def generate_tree_from_commits(
     changelog_release_hook: ChangelogReleaseHook | None = None,
     rules: TagRules | None = None,
     during_version_bump: bool = False,
+    subject_only: bool = False,
 ) -> Generator[dict[str, Any], None, None]:
     pat = re.compile(changelog_pattern)
     map_pat = re.compile(commit_parser, re.MULTILINE)
@@ -147,11 +148,15 @@ def generate_tree_from_commits(
         if not pat.match(commit.message):
             continue
 
-        # Process subject and body from commit message
-        for message in chain(
-            [map_pat.match(commit.message)],
-            (body_map_pat.match(block) for block in commit.body.split("\n\n")),
-        ):
+        # Process subject; optionally also parse body blocks for nested entries
+        # (legacy default behaviour, controlled by `changelog_subject_only`).
+        subject_match = map_pat.match(commit.message)
+        body_matches: Iterable[re.Match[str] | None] = (
+            ()
+            if subject_only
+            else (body_map_pat.match(block) for block in commit.body.split("\n\n"))
+        )
+        for message in chain([subject_match], body_matches):
             if message:
                 process_commit_message(
                     changelog_message_builder_hook,

commitizen/commands/changelog.py

@@ -276,6 +276,7 @@ def __call__(self) -> None:
             changelog_release_hook=self.cz.changelog_release_hook,
             rules=self.tag_rules,
             during_version_bump=self.during_version_bump,
+            subject_only=self.config.settings["changelog_subject_only"],
         )
         if self.change_type_order:
             tree = changelog.generate_ordered_changelog_tree(

commitizen/defaults.py

@@ -41,6 +41,7 @@ class Settings(TypedDict, total=False):
     changelog_incremental: bool
     changelog_merge_prerelease: bool
     changelog_start_rev: str | None
+    changelog_subject_only: bool
     customize: CzSettings
     encoding: str
     extras: dict[str, Any]
@@ -103,6 +104,7 @@ class Settings(TypedDict, total=False):
     "changelog_incremental": False,
     "changelog_start_rev": None,
     "changelog_merge_prerelease": False,
+    "changelog_subject_only": False,
     "update_changelog_on_bump": False,
     "use_shortcuts": False,
     "major_version_zero": False,

docs/commands/changelog.md

@@ -147,6 +147,26 @@ This flag can be set in the configuration file with the key `changelog_merge_pre
 changelog_merge_prerelease = true
 ```
 
+### `changelog_subject_only`
+
+By default, Commitizen parses both the subject line and any `\n\n`-separated body blocks of each commit against `commit_parser`, so a commit such as
+
+```
+feat: new feature
+
+refactor: incidental cleanup
+```
+
+produces *two* changelog entries (one under `feat`, one under `refactor`). Set this configuration to `true` to limit changelog parsing to the subject line only.
+
+```toml
+[tool.commitizen]
+# ...
+changelog_subject_only = true
+```
+
+The default (`false`) preserves the historical behaviour.
+
 ### `--template`
 
 Provide your own changelog Jinja template by using the `template` settings or the `--template` parameter.

tests/test_changelog.py

@@ -1191,6 +1191,41 @@ def test_generate_tree_from_commits_with_no_commits(tags):
     assert tuple(tree) == ({"changes": {}, "date": "", "version": "Unreleased"},)
 
 
+def test_generate_tree_from_commits_subject_only_skips_body_blocks(tags):
+    """`subject_only=True` ignores parser-matching blocks inside `commit.body`.
+
+    Regression for #1267 where, e.g., a commit subject `feat: new feature`
+    with a body containing `refactor: cleanup` produced two changelog
+    entries instead of one.
+    """
+    parser = ConventionalCommitsCz.commit_parser
+    changelog_pattern = ConventionalCommitsCz.bump_pattern
+
+    commit = git.GitCommit(
+        rev="abc123",
+        title="feat: new feature",
+        body="some prose\n\nrefactor: incidental cleanup",
+        author="Commitizen",
+        author_email="author@cz.dev",
+    )
+
+    default_tree = list(
+        changelog.generate_tree_from_commits([commit], tags, parser, changelog_pattern)
+    )
+    assert default_tree[0]["changes"].keys() == {"feat", "refactor"}
+
+    subject_only_tree = list(
+        changelog.generate_tree_from_commits(
+            [commit],
+            tags,
+            parser,
+            changelog_pattern,
+            subject_only=True,
+        )
+    )
+    assert subject_only_tree[0]["changes"].keys() == {"feat"}
+
+
 @pytest.mark.parametrize(
     ("change_type_order", "expected_reordering"),
     [