-p option now can be used to early-load plugins by entry-point name

Fixes #4718

changelog/4718.feature.rst

@@ -0,0 +1,6 @@
+The ``-p`` option can now be used to early-load plugins also by entry-point name, instead of just
+by module name.
+
+This makes it possible to early load external plugins like ``pytest-cov`` in the command-line::
+
+    pytest -p pytest_cov

changelog/4718.trivial.rst

@@ -0,0 +1 @@
+``pluggy>=0.9`` is now required.

doc/en/plugins.rst

@@ -27,7 +27,7 @@ Here is a little annotated list for some popular plugins:
   for `twisted <http://twistedmatrix.com>`_ apps, starting a reactor and
   processing deferreds from test functions.
 
-* `pytest-cov <https://pypi.org/project/pytest-cov/>`_:
+* `pytest-cov <https://pypi.org/project/pytest-cov/>`__:
   coverage reporting, compatible with distributed testing
 
 * `pytest-xdist <https://pypi.org/project/pytest-xdist/>`_:

doc/en/usage.rst

@@ -680,6 +680,22 @@ for example ``-x`` if you only want to send one particular failure.
 
 Currently only pasting to the http://bpaste.net service is implemented.
 
+Early loading plugins
+---------------------
+
+You can early-load plugins (internal and external) explicitly in the command-line with the ``-p`` option::
+
+    pytest -p mypluginmodule
+
+The option receives a ``name`` parameter, which can be:
+
+* A full module dotted name, for example ``myproject.plugins``. This dotted name must be importable.
+* The entry-point name of a plugin. This is the name passed to ``setuptools`` when the plugin is
+  registered. For example to early-load the `pytest-cov <https://pypi.org/project/pytest-cov/>`__ plugin you can use::
+
+    pytest -p pytest_cov
+
+
 Disabling plugins
 -----------------
 

setup.py

@@ -22,7 +22,7 @@ INSTALL_REQUIRES = [
 # if _PYTEST_SETUP_SKIP_PLUGGY_DEP is set, skip installing pluggy;
 # used by tox.ini to test with pluggy master
 if "_PYTEST_SETUP_SKIP_PLUGGY_DEP" not in os.environ:
-    INSTALL_REQUIRES.append("pluggy>=0.7")
+    INSTALL_REQUIRES.append("pluggy>=0.9")
 
 
 def main():

src/_pytest/config/__init__.py

@@ -497,7 +497,7 @@ class PytestPluginManager(PluginManager):
             if not name.startswith("pytest_"):
                 self.set_blocked("pytest_" + name)
         else:
-            self.import_plugin(arg)
+            self.import_plugin(arg, consider_entry_points=True)
 
     def consider_conftest(self, conftestmodule):
         self.register(conftestmodule, name=conftestmodule.__file__)
@@ -513,7 +513,11 @@ class PytestPluginManager(PluginManager):
         for import_spec in plugins:
             self.import_plugin(import_spec)
 
-    def import_plugin(self, modname):
+    def import_plugin(self, modname, consider_entry_points=False):
+        """
+        Imports a plugin with ``modname``. If ``consider_entry_points`` is True, entry point
+        names are also considered to find a plugin.
+        """
         # most often modname refers to builtin modules, e.g. "pytester",
         # "terminal" or "capture".  Those plugins are registered under their
         # basename for historic purposes but must be imported with the
@@ -524,22 +528,26 @@ class PytestPluginManager(PluginManager):
         modname = str(modname)
         if self.is_blocked(modname) or self.get_plugin(modname) is not None:
             return
-        if modname in builtin_plugins:
-            importspec = "_pytest." + modname
-        else:
-            importspec = modname
+
+        importspec = "_pytest." + modname if modname in builtin_plugins else modname
         self.rewrite_hook.mark_rewrite(importspec)
+
+        if consider_entry_points:
+            loaded = self.load_setuptools_entrypoints("pytest11", name=modname)
+            if loaded:
+                return
+
         try:
             __import__(importspec)
         except ImportError as e:
-            new_exc_type = ImportError
             new_exc_message = 'Error importing plugin "%s": %s' % (
                 modname,
                 safe_str(e.args[0]),
             )
-            new_exc = new_exc_type(new_exc_message)
+            new_exc = ImportError(new_exc_message)
+            tb = sys.exc_info()[2]
 
-            six.reraise(new_exc_type, new_exc, sys.exc_info()[2])
+            six.reraise(ImportError, new_exc, tb)
 
         except Skipped as e:
             from _pytest.warnings import _issue_warning_captured

src/_pytest/helpconfig.py

@@ -60,7 +60,7 @@ def pytest_addoption(parser):
         dest="plugins",
         default=[],
         metavar="name",
-        help="early-load given plugin (multi-allowed). "
+        help="early-load given plugin module name or entry point (multi-allowed). "
         "To avoid loading of plugins, use the `no:` prefix, e.g. "
         "`no:doctest`.",
     )

testing/acceptance_test.py

@@ -8,6 +8,7 @@ import sys
 import textwrap
 import types
 
+import attr
 import py
 import six
 
@@ -108,6 +109,60 @@ class TestGeneralUsage(object):
         assert result.ret == 0
         result.stdout.fnmatch_lines(["*1 passed*"])
 
+    @pytest.mark.parametrize("load_cov_early", [True, False])
+    def test_early_load_setuptools_name(self, testdir, monkeypatch, load_cov_early):
+        pkg_resources = pytest.importorskip("pkg_resources")
+
+        testdir.makepyfile(mytestplugin1_module="")
+        testdir.makepyfile(mytestplugin2_module="")
+        testdir.makepyfile(mycov_module="")
+        testdir.syspathinsert()
+
+        loaded = []
+
+        @attr.s
+        class DummyEntryPoint(object):
+            name = attr.ib()
+            module = attr.ib()
+            version = "1.0"
+
+            @property
+            def project_name(self):
+                return self.name
+
+            def load(self):
+                __import__(self.module)
+                loaded.append(self.name)
+                return sys.modules[self.module]
+
+            @property
+            def dist(self):
+                return self
+
+            def _get_metadata(self, *args):
+                return []
+
+        entry_points = [
+            DummyEntryPoint("myplugin1", "mytestplugin1_module"),
+            DummyEntryPoint("myplugin2", "mytestplugin2_module"),
+            DummyEntryPoint("mycov", "mycov_module"),
+        ]
+
+        def my_iter(group, name=None):
+            assert group == "pytest11"
+            for ep in entry_points:
+                if name is not None and ep.name != name:
+                    continue
+                yield ep
+
+        monkeypatch.setattr(pkg_resources, "iter_entry_points", my_iter)
+        params = ("-p", "mycov") if load_cov_early else ()
+        testdir.runpytest_inprocess(*params)
+        if load_cov_early:
+            assert loaded == ["mycov", "myplugin1", "myplugin2"]
+        else:
+            assert loaded == ["myplugin1", "myplugin2", "mycov"]
+
     def test_assertion_magic(self, testdir):
         p = testdir.makepyfile(
             """

testing/test_config.py

@@ -5,6 +5,8 @@ from __future__ import print_function
 import sys
 import textwrap
 
+import attr
+
 import _pytest._code
 import pytest
 from _pytest.config import _iter_rewritable_modules
@@ -622,7 +624,28 @@ def test_disable_plugin_autoload(testdir, monkeypatch, parse_args, should_load):
     pkg_resources = pytest.importorskip("pkg_resources")
 
     def my_iter(group, name=None):
-        raise AssertionError("Should not be called")
+        assert group == "pytest11"
+        assert name == "mytestplugin"
+        return iter([DummyEntryPoint()])
+
+    @attr.s
+    class DummyEntryPoint(object):
+        name = "mytestplugin"
+        version = "1.0"
+
+        @property
+        def project_name(self):
+            return self.name
+
+        def load(self):
+            return sys.modules[self.name]
+
+        @property
+        def dist(self):
+            return self
+
+        def _get_metadata(self, *args):
+            return []
 
     class PseudoPlugin(object):
         x = 42