fix coverage output from synthetic packages (#71727)

* fix coverage output from synthetic packages

* synthetic packages (eg, implicit collection packages without `__init__.py`) were always created at runtime with empty string source, which was compiled to a code object and exec'd during the package load. When run with code coverage, it created a bogus coverage entry (since the `__synthetic__`-suffixed `__file__` entry didn't exist on disk).
* modified collection loader `get_code` to preserve the distinction between `None` (eg synthetic package) and empty string (eg empty `__init__.py`) values from `get_source`, and to return `None` when the source is `None`. This allows the package loader to skip `exec`ing things that truly have no source file on disk, thus not creating bogus coverage entries, while preserving behavior and coverage reporting for empty package inits that actually exist.

* add unit test

1 files changed, 16 insertions, 0 deletions

diff --git a/test/units/utils/collection_loader/test_collection_loader.py b/test/units/utils/collection_loader/test_collection_loader.py
index 496dc5416e..6488188c08 100644
--- a/test/units/utils/collection_loader/test_collection_loader.py
+++ b/test/units/utils/collection_loader/test_collection_loader.py
@@ -594,6 +594,22 @@ def test_bogus_imports():
             import_module(bogus_import)
 
 
+def test_empty_vs_no_code():
+    finder = get_default_finder()
+    reset_collections_loader_state(finder)
+
+    from ansible_collections.testns import testcoll  # synthetic package with no code on disk
+    from ansible_collections.testns.testcoll.plugins import module_utils  # real package with empty code file
+
+    # ensure synthetic packages have no code object at all (prevent bogus coverage entries)
+    assert testcoll.__loader__.get_source(testcoll.__name__) is None
+    assert testcoll.__loader__.get_code(testcoll.__name__) is None
+
+    # ensure empty package inits do have a code object
+    assert module_utils.__loader__.get_source(module_utils.__name__) == b''
+    assert module_utils.__loader__.get_code(module_utils.__name__) is not None
+
+
 def test_finder_playbook_paths():
     finder = get_default_finder()
     reset_collections_loader_state(finder)