Fix pytest_ignore_collect hooks: do not return False

It should only return `True` when something is to be ignored, not
`False` otherwise typically.

This caused e.g. bad interaction with the cacheprovider (before
pytest-dev#6448).

Author: blueyed

src/_pytest/hookspec.py

@@ -198,7 +198,8 @@ def pytest_ignore_collect(path, config):
     This hook is consulted for all files and directories prior to calling
     more specific hooks.
 
-    Stops at first non-None result, see :ref:`firstresult`
+    Stops at first non-None result, see :ref:`firstresult`, i.e. you should
+    only return `False` if the file should never get ignored (by other hooks).
 
     :param path: a :py:class:`py.path.local` - the path to analyze
     :param _pytest.config.Config config: pytest config object

src/_pytest/main.py

@@ -320,8 +320,6 @@ def pytest_ignore_collect(path, config):
     if not allow_in_venv and _in_venv(path):
         return True
 
-    return False
-
 
 def pytest_collection_modifyitems(items, config):
     deselect_prefixes = tuple(config.getoption("deselect") or [])