Making it possible to access the pluginmanager in the pytest_ad… (#6106)

Making it possible to access the pluginmanager in the pytest_addoptio…

5 files changed, 93 insertions, 2 deletions

diff --git a/changelog/6061.feature.rst b/changelog/6061.feature.rst
new file mode 100644
index 000000000..11f548625
--- /dev/null
+++ b/changelog/6061.feature.rst
@@ -0,0 +1,4 @@
+Adding the pluginmanager as an option ``pytest_addoption``
+so that hooks can be invoked when setting up command line options. This is
+useful for having one plugin communicate things to another plugin,
+such as default values or which set of command line options to add.
diff --git a/doc/en/writing_plugins.rst b/doc/en/writing_plugins.rst
index 5f429c219..8660746bd 100644
--- a/doc/en/writing_plugins.rst
+++ b/doc/en/writing_plugins.rst
@@ -677,6 +677,56 @@ Example:
         print(config.hook)
 
 
+.. _`addoptionhooks`:
+
+
+Using hooks in pytest_addoption
+-------------------------------
+
+Occasionally, it is necessary to change the way in which command line options
+are defined by one plugin based on hooks in another plugin. For example,
+a plugin may expose a command line option for which another plugin needs
+to define the default value. The pluginmanager can be used to install and
+use hooks to accomplish this. The plugin would define and add the hooks
+and use pytest_addoption as follows:
+
+.. code-block:: python
+
+   # contents of hooks.py
+
+   # Use firstresult=True because we only want one plugin to define this
+   # default value
+   @hookspec(firstresult=True)
+   def pytest_config_file_default_value():
+       """ Return the default value for the config file command line option. """
+
+
+   # contents of myplugin.py
+
+
+   def pytest_addhooks(pluginmanager):
+       """ This example assumes the hooks are grouped in the 'hooks' module. """
+       from . import hook
+
+       pluginmanager.add_hookspecs(hook)
+
+
+   def pytest_addoption(parser, pluginmanager):
+       default_value = pluginmanager.hook.pytest_config_file_default_value()
+       parser.addoption(
+           "--config-file",
+           help="Config file to use, defaults to %(default)s",
+           default=default_value,
+       )
+
+The conftest.py that is using myplugin would simply define the hook as follows:
+
+.. code-block:: python
+
+    def pytest_config_file_default_value():
+        return "config.yaml"
+
+
 Optionally using hooks from 3rd party plugins
 ---------------------------------------------
 
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 2b0f48c07..8e11b56e5 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -705,7 +705,9 @@ class Config:
         self._cleanup = []  # type: List[Callable[[], None]]
         self.pluginmanager.register(self, "pytestconfig")
         self._configured = False
-        self.hook.pytest_addoption.call_historic(kwargs=dict(parser=self._parser))
+        self.hook.pytest_addoption.call_historic(
+            kwargs=dict(parser=self._parser, pluginmanager=self.pluginmanager)
+        )
 
     @property
     def invocation_dir(self):
diff --git a/src/_pytest/hookspec.py b/src/_pytest/hookspec.py
index 7a21837bd..8b45c5f9b 100644
--- a/src/_pytest/hookspec.py
+++ b/src/_pytest/hookspec.py
@@ -35,7 +35,7 @@ def pytest_plugin_registered(plugin, manager):
 
 
 @hookspec(historic=True)
-def pytest_addoption(parser):
+def pytest_addoption(parser, pluginmanager):
     """register argparse-style options and ini-style config values,
     called once at the beginning of a test run.
 
@@ -50,6 +50,11 @@ def pytest_addoption(parser):
         To add ini-file values call :py:func:`parser.addini(...)
         <_pytest.config.Parser.addini>`.
 
+    :arg _pytest.config.PytestPluginManager pluginmanager: pytest plugin manager,
+        which can be used to install :py:func:`hookspec`'s or :py:func:`hookimpl`'s
+        and allow one plugin to call another plugin's hooks to change how
+        command line options are added.
+
     Options can later be accessed through the
     :py:class:`config <_pytest.config.Config>` object, respectively:
 
diff --git a/testing/test_pluginmanager.py b/testing/test_pluginmanager.py
index 97f220ca5..836b458c6 100644
--- a/testing/test_pluginmanager.py
+++ b/testing/test_pluginmanager.py
@@ -135,6 +135,36 @@ class TestPytestPluginInteractions:
         ihook_b = session.gethookproxy(testdir.tmpdir.join("tests"))
         assert ihook_a is not ihook_b
 
+    def test_hook_with_addoption(self, testdir):
+        """Test that hooks can be used in a call to pytest_addoption"""
+        testdir.makepyfile(
+            newhooks="""
+            import pytest
+            @pytest.hookspec(firstresult=True)
+            def pytest_default_value():
+                pass
+        """
+        )
+        testdir.makepyfile(
+            myplugin="""
+            import newhooks
+            def pytest_addhooks(pluginmanager):
+                pluginmanager.add_hookspecs(newhooks)
+            def pytest_addoption(parser, pluginmanager):
+                default_value = pluginmanager.hook.pytest_default_value()
+                parser.addoption("--config", help="Config, defaults to %(default)s", default=default_value)
+        """
+        )
+        testdir.makeconftest(
+            """
+            pytest_plugins=("myplugin",)
+            def pytest_default_value():
+                return "default_value"
+        """
+        )
+        res = testdir.runpytest("--help")
+        res.stdout.fnmatch_lines(["*--config=CONFIG*default_value*"])
+
 
 def test_default_markers(testdir):
     result = testdir.runpytest("--markers")