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

changelogs/fragments/fix_bogus_coverage.yml

@@ -0,0 +1,2 @@
+bugfixes:
+- collection loader - fix bogus code coverage entries for synthetic packages

lib/ansible/utils/collection_loader/_collection_finder.py

@@ -355,7 +355,9 @@ class _AnsibleCollectionPkgLoaderBase:
 
         with self._new_or_existing_module(fullname, **module_attrs) as module:
             # execute the module's code in its namespace
-            exec(self.get_code(fullname), module.__dict__)
+            code_obj = self.get_code(fullname)
+            if code_obj is not None:  # things like NS packages that can't have code on disk will return None
+                exec(code_obj, module.__dict__)
 
             return module
 
@@ -428,8 +430,11 @@ class _AnsibleCollectionPkgLoaderBase:
             filename = '<string>'
 
         source_code = self.get_source(fullname)
-        if not source_code:
-            source_code = ''
+
+        # for things like synthetic modules that really have no source on disk, don't return a code object at all
+        # vs things like an empty package init (which has an empty string source on disk)
+        if source_code is None:
+            return None
 
         self._compiled_code = compile(source=source_code, filename=filename, mode='exec', flags=0, dont_inherit=True)
 

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)