Implemented the dynamic scope feature.

testing/python/fixtures.py

@@ -2216,6 +2216,68 @@ class TestFixtureMarker:
             ["*ScopeMismatch*You tried*function*session*request*"]
         )
 
+    def test_dynamic_scope(self, testdir):
+        testdir.makeconftest(
+            """
+            import pytest
+
+
+            def pytest_addoption(parser):
+                parser.addoption("--extend-scope", action="store_true", default=False)
+
+
+            def dynamic_scope(fixture_name, config):
+                if config.getoption("--extend-scope"):
+                    return "session"
+                return "function"
+
+
+            @pytest.fixture(scope=dynamic_scope)
+            def dynamic_fixture(calls=[]):
+                calls.append("call")
+                return len(calls)
+
+        """
+        )
+
+        testdir.makepyfile(
+            """
+            def test_first(dynamic_fixture):
+                assert dynamic_fixture == 1
+
+
+            def test_second(dynamic_fixture):
+                assert dynamic_fixture == 2
+
+        """
+        )
+
+        reprec = testdir.inline_run()
+        reprec.assertoutcome(passed=2)
+
+        reprec = testdir.inline_run("--extend-scope")
+        reprec.assertoutcome(passed=1, failed=1)
+
+    def test_dynamic_scope_bad_return(self, testdir):
+        testdir.makepyfile(
+            """
+            import pytest
+
+            def dynamic_scope(**_):
+                return "wrong-scope"
+
+            @pytest.fixture(scope=dynamic_scope)
+            def fixture():
+                pass
+
+        """
+        )
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(
+            "Fixture 'fixture' from test_dynamic_scope_bad_return.py "
+            "got an unexpected scope value 'wrong-scope'"
+        )
+
     def test_register_only_with_mark(self, testdir):
         testdir.makeconftest(
             """
@@ -4009,3 +4071,54 @@ def test_fixture_named_request(testdir):
             "  *test_fixture_named_request.py:5",
         ]
     )
+
+
+def test_fixture_duplicated_arguments(testdir):
+    testdir.makepyfile(
+        """
+        import pytest
+
+        with pytest.raises(TypeError) as excinfo:
+
+            @pytest.fixture("session", scope="session")
+            def arg(arg):
+                pass
+
+        def test_error():
+            assert (
+                str(excinfo.value)
+                == "The fixture arguments are defined as positional and keyword: scope. "
+                "Use only keyword arguments."
+            )
+
+    """
+    )
+
+    reprec = testdir.inline_run()
+    reprec.assertoutcome(passed=1)
+
+
+def test_fixture_with_positionals(testdir):
+    """Raise warning, but the positionals should still works."""
+    testdir.makepyfile(
+        """
+        import os
+
+        import pytest
+        from _pytest.deprecated import FIXTURE_POSITIONAL_ARGUMENTS
+
+        with pytest.warns(pytest.PytestDeprecationWarning) as warnings:
+            @pytest.fixture("function", [0], True)
+            def arg(monkeypatch):
+                monkeypatch.setenv("AUTOUSE_WORKS", "1")
+
+
+        def test_autouse():
+            assert os.environ.get("AUTOUSE_WORKS") == "1"
+            assert str(warnings[0].message) == str(FIXTURE_POSITIONAL_ARGUMENTS)
+
+    """
+    )
+
+    reprec = testdir.inline_run()
+    reprec.assertoutcome(passed=1)