From c8d52b633b6a7423633042c0eec3c67483ac13a3 Mon Sep 17 00:00:00 2001
From: Bruno Oliveira <nicoddemus@gmail.com>
Date: Tue, 21 Nov 2017 22:49:46 -0200
Subject: [PATCH] Fix assertion rewrite to match module names correctly

Fix #2939
---
 _pytest/assertion/rewrite.py |  2 +-
 changelog/2939.bugfix        |  1 +
 testing/test_assertion.py    | 18 ++++++++++++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 changelog/2939.bugfix

diff --git a/_pytest/assertion/rewrite.py b/_pytest/assertion/rewrite.py
index d48b6648f..27026b0fe 100644
--- a/_pytest/assertion/rewrite.py
+++ b/_pytest/assertion/rewrite.py
@@ -168,7 +168,7 @@ class AssertionRewritingHook(object):
                 return True
 
         for marked in self._must_rewrite:
-            if name.startswith(marked):
+            if name == marked or name.startswith(marked + '.'):
                 state.trace("matched marked file %r (from %r)" % (name, marked))
                 return True
 
diff --git a/changelog/2939.bugfix b/changelog/2939.bugfix
new file mode 100644
index 000000000..8aeedad01
--- /dev/null
+++ b/changelog/2939.bugfix
@@ -0,0 +1 @@
+Fix issue in assertion rewriting which could lead it to rewrite modules which should not be rewritten.
diff --git a/testing/test_assertion.py b/testing/test_assertion.py
index 4cd050d8c..244b47516 100644
--- a/testing/test_assertion.py
+++ b/testing/test_assertion.py
@@ -129,6 +129,24 @@ class TestImportHookInstallation(object):
         result = testdir.runpytest_subprocess('--assert=rewrite')
         assert result.ret == 0
 
+    def test_pytest_plugins_rewrite_module_names_correctly(self, testdir):
+        """Test that we match files correctly when they are marked for rewriting (#2939)."""
+        contents = {
+            'conftest.py': """
+                pytest_plugins = "ham"
+            """,
+            'ham.py': "",
+            'hamster.py': "",
+            'test_foo.py': """
+                def test_foo(pytestconfig):
+                    assert pytestconfig.pluginmanager.rewrite_hook.find_module('ham') is not None
+                    assert pytestconfig.pluginmanager.rewrite_hook.find_module('hamster') is None
+            """,
+        }
+        testdir.makepyfile(**contents)
+        result = testdir.runpytest_subprocess('--assert=rewrite')
+        assert result.ret == 0
+
     @pytest.mark.parametrize('mode', ['plain', 'rewrite'])
     @pytest.mark.parametrize('plugin_state', ['development', 'installed'])
     def test_installed_plugin_rewrite(self, testdir, mode, plugin_state):