From 15fe8c6e9020370b07e4c6d4b0c95e4993b0c511 Mon Sep 17 00:00:00 2001
From: Daniel Hahler <git@thequod.de>
Date: Sat, 16 Mar 2019 15:29:27 +0100
Subject: [PATCH] Handle `-p plug` after `-p no:plug`.

This can be used to override a blocked plugin (e.g. in "addopts") from the
command line etc.
---
 changelog/4936.feature.rst     | 4 ++++
 src/_pytest/config/__init__.py | 8 ++++++++
 testing/test_pluginmanager.py  | 7 +++++++
 3 files changed, 19 insertions(+)
 create mode 100644 changelog/4936.feature.rst

diff --git a/changelog/4936.feature.rst b/changelog/4936.feature.rst
new file mode 100644
index 000000000..744af1297
--- /dev/null
+++ b/changelog/4936.feature.rst
@@ -0,0 +1,4 @@
+Handle ``-p plug`` after ``-p no:plug``.
+
+This can be used to override a blocked plugin (e.g. in "addopts") from the
+command line etc.
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 22eeaa33d..c44392073 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -496,6 +496,14 @@ class PytestPluginManager(PluginManager):
             if not name.startswith("pytest_"):
                 self.set_blocked("pytest_" + name)
         else:
+            name = arg
+            # Unblock the plugin.  None indicates that it has been blocked.
+            # There is no interface with pluggy for this.
+            if self._name2plugin.get(name, -1) is None:
+                del self._name2plugin[name]
+            if not name.startswith("pytest_"):
+                if self._name2plugin.get("pytest_" + name, -1) is None:
+                    del self._name2plugin["pytest_" + name]
             self.import_plugin(arg, consider_entry_points=True)
 
     def consider_conftest(self, conftestmodule):
diff --git a/testing/test_pluginmanager.py b/testing/test_pluginmanager.py
index 80817932e..4e0c0ed1e 100644
--- a/testing/test_pluginmanager.py
+++ b/testing/test_pluginmanager.py
@@ -346,3 +346,10 @@ class TestPytestPluginManagerBootstrapming(object):
         l2 = pytestpm.get_plugins()
         assert 42 not in l2
         assert 43 not in l2
+
+    def test_blocked_plugin_can_be_used(self, pytestpm):
+        pytestpm.consider_preparse(["xyz", "-p", "no:abc", "-p", "abc"])
+
+        assert pytestpm.has_plugin("abc")
+        assert not pytestpm.is_blocked("abc")
+        assert not pytestpm.is_blocked("pytest_abc")