feat(pre-commit): Add commitizen-branch hook

Check all commit messages on the current branch. This is useful for
checking commit messages after the fact (e.g., pre-push or in CI) since
the existing hook only works at commit time. Expand the documentation of
the pre-existing commitizen hook to clarify the relationship between
them.

Author: Kurt-von-Laven

.pre-commit-hooks.yaml

@@ -1,9 +1,27 @@
 - id: commitizen
   name: commitizen check
-  description: "Check whether the commit message follows commiting rules"
+  description: >
+    Check whether the current commit message follows commiting rules. Allow
+    empty commit messages by default, because they typically indicate to Git
+    that the commit should be aborted.
   entry: cz check
   args: [--allow-abort, --commit-msg-file]
   stages: [commit-msg]
   language: python
   language_version: python3
   minimum_pre_commit_version: "1.4.3"
+
+- id: commitizen-branch
+  name: commitizen check branch
+  description: >
+    Check all commit messages that are already on the current branch but not the
+    default branch on the origin repository. Useful for checking messages after
+    the fact (e.g., pre-push or in CI) without an expensive check of the entire
+    repository history.
+  entry: cz check
+  args: [--rev-range, origin/HEAD..HEAD]
+  always_run: true
+  pass_filenames: false
+  language: python
+  language_version: python3
+  minimum_pre_commit_version: "1.4.3"

docs/README.md

@@ -101,7 +101,7 @@ cz commit -s
 ```
 
 ### Integrating with Pre-commit
-Commitizen can lint your commit message for you with `cz check`.
+Commitizen can lint your commit messages for you with `cz check`.
 You can integrate this in your [pre-commit](https://pre-commit.com/) config with:
 
 ```yaml
@@ -111,14 +111,23 @@ repos:
     rev: master
     hooks:
       - id: commitizen
+      - id: commitizen-branch
+        stages: [push]
 ```
 
-After the configuration is added, you'll need to run
+After the configuration is added, you'll need to run:
 
 ```sh
-pre-commit install --hook-type commit-msg
+pre-commit install --hook-type commit-msg pre-push
 ```
 
+If you aren't using both hooks, you needn't install both stages.
+
+| Hook              | Recommended Stage |
+| ----------------- | ----------------- |
+| commitizen        | commit-msg        |
+| commitizen-branch | pre-push          |
+
 Read more about the `check` command [here](check.md).
 
 ### Help