In Trio mode, auto-convert async fixtures to Trio fixtures

The main benefit of this is that it lets us catch more cases where
these fixtures are accidentally misused.

Closes gh-18
Closes gh-51

pytest_trio/_tests/helpers.py

@@ -0,0 +1,15 @@
+import pytest
+
+
+def enable_trio_mode_via_pytest_ini(testdir):
+    testdir.makefile(".ini", pytest="[pytest]\ntrio_mode = true\n")
+
+
+def enable_trio_mode_via_conftest_py(testdir):
+    testdir.makeconftest("from pytest_trio.enable_trio_mode import *")
+
+
+enable_trio_mode = pytest.mark.parametrize(
+    "enable_trio_mode",
+    [enable_trio_mode_via_pytest_ini, enable_trio_mode_via_conftest_py]
+)

pytest_trio/_tests/test_fixture_mistakes.py

@@ -1,6 +1,8 @@
 import pytest
 from pytest_trio import trio_fixture
 
+from .helpers import enable_trio_mode
+
 
 def test_trio_fixture_with_non_trio_test(testdir):
     testdir.makepyfile(
@@ -34,11 +36,11 @@ def test_sync_indirect(indirect_trio_time):
 
     result.assert_outcomes(passed=1, error=2)
     result.stdout.fnmatch_lines(
-        ["*Trio fixtures can only be used by Trio tests*"]
+        ["*: Trio fixtures can only be used by Trio tests*"]
     )
 
 
-def test_trio_fixture_with_wrong_scope(testdir):
+def test_trio_fixture_with_wrong_scope_without_trio_mode(testdir):
     # There's a trick here: when you have a non-function-scope fixture, it's
     # not instantiated for any particular function (obviously). So... when our
     # pytest_fixture_setup hook tries to check for marks, it can't normally
@@ -49,7 +51,6 @@ def test_trio_fixture_with_wrong_scope(testdir):
     testdir.makepyfile(
         """
         import pytest
-        import pytest_trio
 
         @pytest.fixture(scope="class")
         async def async_class_fixture():
@@ -65,4 +66,54 @@ async def test_foo(self, async_class_fixture):
     result = testdir.runpytest()
 
     result.assert_outcomes(error=1)
-    result.stdout.fnmatch_lines(["*must be function-scope*"])
+    result.stdout.fnmatch_lines(["*: Trio fixtures must be function-scope*"])
+
+
+@enable_trio_mode
+def test_trio_fixture_with_wrong_scope_in_trio_mode(testdir, enable_trio_mode):
+    enable_trio_mode(testdir)
+
+    testdir.makepyfile(
+        """
+        import pytest
+
+        @pytest.fixture(scope="session")
+        async def async_session_fixture():
+            pass
+
+
+        async def test_whatever(async_session_fixture):
+            pass
+        """
+    )
+
+    result = testdir.runpytest()
+
+    result.assert_outcomes(error=1)
+    result.stdout.fnmatch_lines(["*: Trio fixtures must be function-scope*"])
+
+
+@enable_trio_mode
+def test_async_fixture_with_sync_test_in_trio_mode(testdir, enable_trio_mode):
+    enable_trio_mode(testdir)
+
+    testdir.makepyfile(
+        """
+        import pytest
+
+        @pytest.fixture
+        async def async_fixture():
+            pass
+
+
+        def test_whatever(async_fixture):
+            pass
+        """
+    )
+
+    result = testdir.runpytest()
+
+    result.assert_outcomes(error=1)
+    result.stdout.fnmatch_lines(
+        ["*: Trio fixtures can only be used by Trio tests*"]
+    )

pytest_trio/_tests/test_trio_mode.py

@@ -1,5 +1,7 @@
 import pytest
 
+from .helpers import enable_trio_mode
+
 test_text = """
 import pytest
 import trio
@@ -26,19 +28,11 @@ async def test_hypothesis_fail(b):
 """
 
 
-def test_trio_mode_pytest_ini(testdir):
-    testdir.makepyfile(test_text)
-
-    testdir.makefile(".ini", pytest="[pytest]\ntrio_mode = true\n")
-
-    result = testdir.runpytest()
-    result.assert_outcomes(passed=2, failed=2)
+@enable_trio_mode
+def test_trio_mode(testdir, enable_trio_mode):
+    enable_trio_mode(testdir)
 
-
-def test_trio_mode_conftest(testdir):
     testdir.makepyfile(test_text)
 
-    testdir.makeconftest("from pytest_trio.enable_trio_mode import *")
-
     result = testdir.runpytest()
     result.assert_outcomes(passed=2, failed=2)

pytest_trio/enable_trio_mode.py

@@ -1,7 +1,11 @@
-__all__ = ["pytest_collection_modifyitems"]
+__all__ = ["pytest_collection_modifyitems", "pytest_fixture_setup"]
 
-from .plugin import automark
+from .plugin import automark, handle_fixture
 
 
 def pytest_collection_modifyitems(items):
     automark(items)
+
+
+def pytest_fixture_setup(fixturedef, request):
+    return handle_fixture(fixturedef, request, force_trio_mode=True)

pytest_trio/plugin.py

@@ -214,22 +214,26 @@ def trio_fixture(func):
     return pytest.fixture(func)
 
 
-def _is_trio_fixture(func, is_trio_test, deps):
+def _is_trio_fixture(func, coerce_async, deps):
     if getattr(func, "_force_trio_fixture", False):
         return True
-    if is_trio_test:
-        if iscoroutinefunction(func) or isasyncgenfunction(func):
-            return True
+    if (coerce_async and
+        (iscoroutinefunction(func) or isasyncgenfunction(func))):
+        return True
     if any(isinstance(dep, TrioFixture) for dep in deps.values()):
         return True
     return False
 
 
-@pytest.hookimpl
-def pytest_fixture_setup(fixturedef, request):
+def handle_fixture(fixturedef, request, force_trio_mode):
     is_trio_test = (request.node.get_closest_marker("trio") is not None)
+    if force_trio_mode:
+        is_trio_mode = True
+    else:
+        is_trio_mode = request.node.config.getini("trio_mode")
+    coerce_async = (is_trio_test or is_trio_mode)
     deps = {dep: request.getfixturevalue(dep) for dep in fixturedef.argnames}
-    if _is_trio_fixture(fixturedef.func, is_trio_test, deps):
+    if _is_trio_fixture(fixturedef.func, coerce_async, deps):
         if request.scope != "function":
             raise RuntimeError("Trio fixtures must be function-scope")
         if not is_trio_test:
@@ -239,6 +243,11 @@ def pytest_fixture_setup(fixturedef, request):
         return fixture
 
 
+@pytest.hookimpl
+def pytest_fixture_setup(fixturedef, request):
+    return handle_fixture(fixturedef, request, force_trio_mode=False)
+
+
 ################################################################
 # Trio mode
 ################################################################