Enable re-writing of setuptools-installed plugins

Hook up the PEP 302 import hook very early in pytest startup so
that it gets installed before setuptools-installed plugins are
imported.  Also iterate over all installed plugins and mark them
for rewriting.  If an installed plugin is already imported then
a warning is issued, we can not break since that might break
existing plugins and the fallback will still be gracefull to
plain asserts.

Some existing tests are failing in this commit because of the new
warning triggered by inline pytest runs due to the hypothesis
plugin already being imported.  The tests will be fixed in the next
commit.

testing/test_assertion.py

@@ -26,6 +26,116 @@ def mock_config():
 def interpret(expr):
     return reinterpret.reinterpret(expr, _pytest._code.Frame(sys._getframe(1)))
 
+
+class TestImportHookInstallation:
+
+    @pytest.mark.parametrize('initial_conftest', [True, False])
+    @pytest.mark.parametrize('mode', ['plain', 'rewrite', 'reinterp'])
+    def test_conftest_assertion_rewrite(self, testdir, initial_conftest, mode):
+        """Test that conftest files are using assertion rewrite on import.
+        (#1619)
+        """
+        testdir.tmpdir.join('foo/tests').ensure(dir=1)
+        conftest_path = 'conftest.py' if initial_conftest else 'foo/conftest.py'
+        contents = {
+            conftest_path: """
+                import pytest
+                @pytest.fixture
+                def check_first():
+                    def check(values, value):
+                        assert values.pop(0) == value
+                    return check
+            """,
+            'foo/tests/test_foo.py': """
+                def test(check_first):
+                    check_first([10, 30], 30)
+            """
+        }
+        testdir.makepyfile(**contents)
+        result = testdir.runpytest_subprocess('--assert=%s' % mode)
+        if mode == 'plain':
+            expected = 'E       AssertionError'
+        elif mode == 'rewrite':
+            expected = '*assert 10 == 30*'
+        elif mode == 'reinterp':
+            expected = '*AssertionError:*was re-run*'
+        else:
+            assert 0
+        result.stdout.fnmatch_lines([expected])
+
+    @pytest.mark.parametrize('mode', ['plain', 'rewrite', 'reinterp'])
+    def test_installed_plugin_rewrite(self, testdir, mode):
+        # Make sure the hook is installed early enough so that plugins
+        # installed via setuptools are re-written.
+        ham = testdir.tmpdir.join('hampkg').ensure(dir=1)
+        ham.join('__init__.py').write("""
+import pytest
+
+@pytest.fixture
+def check_first2():
+    def check(values, value):
+        assert values.pop(0) == value
+    return check
+        """)
+        testdir.makepyfile(
+            spamplugin="""
+            import pytest
+            from hampkg import check_first2
+
+            @pytest.fixture
+            def check_first():
+                def check(values, value):
+                    assert values.pop(0) == value
+                return check
+            """,
+            mainwrapper="""
+            import pytest, pkg_resources
+
+            class DummyDistInfo:
+                project_name = 'spam'
+                version = '1.0'
+
+                def _get_metadata(self, name):
+                    return ['spamplugin.py,sha256=abc,123',
+                            'hampkg/__init__.py,sha256=abc,123']
+
+            class DummyEntryPoint:
+                name = 'spam'
+                module_name = 'spam.py'
+                attrs = ()
+                extras = None
+                dist = DummyDistInfo()
+
+                def load(self, require=True, *args, **kwargs):
+                    import spamplugin
+                    return spamplugin
+
+            def iter_entry_points(name):
+                yield DummyEntryPoint()
+
+            pkg_resources.iter_entry_points = iter_entry_points
+            pytest.main()
+            """,
+            test_foo="""
+            def test(check_first):
+                check_first([10, 30], 30)
+
+            def test2(check_first2):
+                check_first([10, 30], 30)
+            """,
+        )
+        result = testdir.run(sys.executable, 'mainwrapper.py', '-s', '--assert=%s' % mode)
+        if mode == 'plain':
+            expected = 'E       AssertionError'
+        elif mode == 'rewrite':
+            expected = '*assert 10 == 30*'
+        elif mode == 'reinterp':
+            expected = '*AssertionError:*was re-run*'
+        else:
+            assert 0
+        result.stdout.fnmatch_lines([expected])
+
+
 class TestBinReprIntegration:
 
     def test_pytest_assertrepr_compare_called(self, testdir):

testing/test_assertrewrite.py

@@ -12,7 +12,7 @@ if sys.platform.startswith("java"):
 
 import _pytest._code
 from _pytest.assertion import util
-from _pytest.assertion.rewrite import rewrite_asserts, PYTEST_TAG
+from _pytest.assertion.rewrite import rewrite_asserts, PYTEST_TAG, AssertionRewritingHook
 from _pytest.main import EXIT_NOTESTSCOLLECTED
 
 
@@ -524,6 +524,16 @@ def test_rewritten():
         testdir.makepyfile("import a_package_without_init_py.module")
         assert testdir.runpytest().ret == EXIT_NOTESTSCOLLECTED
 
+    def test_rewrite_warning(self, pytestconfig, monkeypatch):
+        hook = AssertionRewritingHook(pytestconfig)
+        warnings = []
+        def mywarn(code, msg):
+            warnings.append((code, msg))
+        monkeypatch.setattr(hook.config, 'warn', mywarn)
+        hook.mark_rewrite('_pytest')
+        assert '_pytest' in warnings[0][1]
+
+
 class TestAssertionRewriteHookDetails(object):
     def test_loader_is_package_false_for_module(self, testdir):
         testdir.makepyfile(test_fun="""
@@ -704,40 +714,6 @@ class TestAssertionRewriteHookDetails(object):
         result = testdir.runpytest()
         result.stdout.fnmatch_lines('*1 passed*')
 
-    @pytest.mark.parametrize('initial_conftest', [True, False])
-    @pytest.mark.parametrize('mode', ['plain', 'rewrite', 'reinterp'])
-    def test_conftest_assertion_rewrite(self, testdir, initial_conftest, mode):
-        """Test that conftest files are using assertion rewrite on import.
-        (#1619)
-        """
-        testdir.tmpdir.join('foo/tests').ensure(dir=1)
-        conftest_path = 'conftest.py' if initial_conftest else 'foo/conftest.py'
-        contents = {
-            conftest_path: """
-                import pytest
-                @pytest.fixture
-                def check_first():
-                    def check(values, value):
-                        assert values.pop(0) == value
-                    return check
-            """,
-            'foo/tests/test_foo.py': """
-                def test(check_first):
-                    check_first([10, 30], 30)
-            """
-        }
-        testdir.makepyfile(**contents)
-        result = testdir.runpytest_subprocess('--assert=%s' % mode)
-        if mode == 'plain':
-            expected = 'E       AssertionError'
-        elif mode == 'rewrite':
-            expected = '*assert 10 == 30*'
-        elif mode == 'reinterp':
-            expected = '*AssertionError:*was re-run*'
-        else:
-            assert 0
-        result.stdout.fnmatch_lines([expected])
-
 
 def test_issue731(testdir):
     testdir.makepyfile("""

testing/test_config.py

@@ -373,10 +373,14 @@ def test_preparse_ordering_with_setuptools(testdir, monkeypatch):
     pkg_resources = pytest.importorskip("pkg_resources")
     def my_iter(name):
         assert name == "pytest11"
+        class Dist:
+            project_name = 'spam'
+            version = '1.0'
+            def _get_metadata(self, name):
+                return ['foo.txt,sha256=abc,123']
         class EntryPoint:
             name = "mytestplugin"
-            class dist:
-                pass
+            dist = Dist()
             def load(self):
                 class PseudoPlugin:
                     x = 42
@@ -412,8 +416,14 @@ def test_plugin_preparse_prevents_setuptools_loading(testdir, monkeypatch):
     pkg_resources = pytest.importorskip("pkg_resources")
     def my_iter(name):
         assert name == "pytest11"
+        class Dist:
+            project_name = 'spam'
+            version = '1.0'
+            def _get_metadata(self, name):
+                return ['foo.txt,sha256=abc,123']
         class EntryPoint:
             name = "mytestplugin"
+            dist = Dist()
             def load(self):
                 assert 0, "should not arrive here"
         return iter([EntryPoint()])
@@ -505,7 +515,6 @@ def test_load_initial_conftest_last_ordering(testdir):
     expected = [
         "_pytest.config",
         'test_config',
-        '_pytest.assertion',
         '_pytest.capture',
     ]
     assert [x.function.__module__ for x in l] == expected