feat(plugins): Switch to an importlib.metadata.EntryPoint-based plugin loading

Plugins are now loaded using the `commitizen.plugin` entrypoint
while legacy plugin are not loaded anymore but a warning is raised when one is seen.

Fixes #495

BREAKING CHANGE: Plugins are now exposed as `commitizen.plugin` entrypoints

Author: noirbizarre

Diff for: commitizen/cz/__init__.py

@@ -1,15 +1,18 @@
+from __future__ import annotations
+
 import importlib
 import pkgutil
 import warnings
-from typing import Dict, Iterable, Type
+from typing import Iterable, Optional
+
+import importlib_metadata as metadata
 
 from commitizen.cz.base import BaseCommitizen
-from commitizen.cz.conventional_commits import ConventionalCommitsCz
-from commitizen.cz.customize import CustomizeCommitsCz
-from commitizen.cz.jira import JiraSmartCz
 
 
-def discover_plugins(path: Iterable[str] = None) -> Dict[str, Type[BaseCommitizen]]:
+def discover_plugins(
+    path: Optional[Iterable[str]] = None,
+) -> dict[str, type[BaseCommitizen]]:
     """Discover commitizen plugins on the path
 
     Args:
@@ -19,21 +22,19 @@ def discover_plugins(path: Iterable[str] = None) -> Dict[str, Type[BaseCommitize
     Returns:
         Dict[str, Type[BaseCommitizen]]: Registry with found plugins
     """
-    plugins = {}
-    for _finder, name, _ispkg in pkgutil.iter_modules(path):
-        try:
-            if name.startswith("cz_"):
-                plugins[name] = importlib.import_module(name).discover_this
-        except AttributeError as e:
-            warnings.warn(UserWarning(e.args[0]))
-            continue
-    return plugins
-
-
-registry: Dict[str, Type[BaseCommitizen]] = {
-    "cz_conventional_commits": ConventionalCommitsCz,
-    "cz_jira": JiraSmartCz,
-    "cz_customize": CustomizeCommitsCz,
-}
-
-registry.update(discover_plugins())
+    for _, name, _ in pkgutil.iter_modules(path):
+        if name.startswith("cz_"):
+            mod = importlib.import_module(name)
+            if hasattr(mod, "discover_this"):
+                warnings.warn(
+                    UserWarning(
+                        f"Legacy plugin '{name}' has been ignored: please expose it the 'commitizen.plugin' entrypoint"
+                    )
+                )
+
+    return {
+        ep.name: ep.load() for ep in metadata.entry_points(group="commitizen.plugin")
+    }
+
+
+registry: dict[str, type[BaseCommitizen]] = discover_plugins()

Diff for: docs/customization.md

@@ -190,8 +190,8 @@ The basic steps are:
 
 1. Inheriting from `BaseCommitizen`
 2. Give a name to your rules.
-3. Expose the class at the end of your file assigning it to `discover_this`
-4. Create a python package starting with `cz_` using `setup.py`, `poetry`, etc
+3. Create a python package using `setup.py`, `poetry`, etc
+4. Expose the class as a `commitizen.plugin` entrypoint
 
 Check an [example](convcomms) on how to configure `BaseCommitizen`.
 
@@ -205,7 +205,7 @@ See [commitizen_cz_template](https://github.com/commitizen-tools/commitizen_cz_t
 
 ### Custom commit rules
 
-Create a file starting with `cz_`, for example `cz_jira.py`. This prefix is used to detect the plug-in. Same method [flask uses]
+Create a Python module, for example `cz_jira.py`.
 
 Inherit from `BaseCommitizen`, and you must define `questions` and `message`. The others are optional.
 
@@ -257,8 +257,6 @@ class JiraCz(BaseCommitizen):
         """
         return 'We use this because is useful'
 
-
-discover_this = JiraCz  # used by the plug-in system
 ```
 
 The next file required is `setup.py` modified from flask version.
@@ -272,7 +270,12 @@ setup(
     py_modules=['cz_jira'],
     license='MIT',
     long_description='this is a long description',
-    install_requires=['commitizen']
+    install_requires=['commitizen'],
+    entry_points = {
+        'commitizen.plugin': [
+            'cz_jira = cz_jira:JiraCz'
+        ]
+    }
 )
 ```
 
@@ -287,8 +290,6 @@ doing `pip install .`
 
 If you feel like it should be part of this repo, create a PR.
 
-[flask uses]: http://flask.pocoo.org/docs/0.12/extensiondev/
-
 ### Custom bump rules
 
 You need to define 2 parameters inside your custom `BaseCommitizen`.
@@ -381,3 +382,56 @@ from commitizen.cz.exception import CzException
 class NoSubjectProvidedException(CzException):
     ...
 ```
+
+### Migrating from legacy plugin format
+
+Commitizen migrated to a new plugin format relying on `importlib.metadata.EntryPoint`.
+Migration should be straight-forward for legacy plugins:
+
+- Remove the `discover_this` line from you plugin module
+- Expose the plugin class under as a `commitizen.plugin` entrypoint.
+
+The name of the plugin is now determined by the name of the entrypoint.
+
+#### Example
+
+If you were having a `CzPlugin` class in a `cz_plugin.py` module like this:
+
+```python
+from commitizen.cz.base import BaseCommitizen
+
+class PluginCz(BaseCommitizen):
+    ...
+
+discover_this = PluginCz
+```
+
+Then remove the `discover_this` line:
+
+```python
+from commitizen.cz.base import BaseCommitizen
+
+class PluginCz(BaseCommitizen):
+    ...
+```
+
+and expose the class as entrypoint in you setuptools:
+
+```python
+from setuptools import setup
+
+setup(
+    name='MyPlugin',
+    version='0.1.0',
+    py_modules=['cz_plugin'],
+    ...
+    entry_points = {
+        'commitizen.plugin': [
+            'plugin = cz_plugin:PluginCz'
+        ]
+    }
+    ...
+)
+```
+
+Then your plugin will be available under the name `plugin`.