building: BUNDLE: exempt collected .py/.pyc files from relocation

In macOS .app bundles, exempt the .py and .pyc files that are
collected as DATA files from being relocated from Contents/MacOS
to Contents/Resources (and then symlinked back).

In certain scenarios (such as OpenCV loader's code), the path to
a .py file needs to resolve to the directory that contains the
adjacent binary extensions; i.e., the original directory in
Contents/MacOS, beaucse the extensions are not relocated.

This might introduce regressions with bundle signing and
notarization that we cannot test, hence the breaking change
news entry. But to my knowledge, the main source of problems with
that are dots in the directory names, which should not be the
problem with directory- and base names of the collected .py/.pyc
files.

PyInstaller/building/osx.py

@@ -192,7 +192,12 @@ def assemble(self):
                     strict_arch_validation=(typ == 'EXTENSION'),
                 )
             # Add most data files to a list for symlinking later.
-            if typ == 'DATA' and base_path not in _QT_BASE_PATH:
+            # Exempt python source files from this relocation, because their real path might need to resolve
+            # to the directory that also contains the extension module.
+            relocate_file = type == 'DATA' and base_path not in _QT_BASE_PATH
+            if relocate_file and os.path.splitext(inm)[1].lower() in {'.py', '.pyc'}:
+                relocate_file = False
+            if relocate_file:
                 links.append((inm, fnm))
             else:
                 tofnm = os.path.join(self.name, "Contents", "MacOS", inm)

news/7180.breaking.rst

@@ -0,0 +1,6 @@
+(macOS) In generated macOS .app bundles, the collected source .py files
+are not relocated from ``Contents/MacOS`` to ``Contents/Resources``
+anymore, to avoid issues when the path to a .py file is supposed to
+resolve to the same directory as adjacent binary extensions. On the
+other hand, this change might result in regressions w.r.t. bundle
+signing and/or notarization.

news/7180.bugfix.rst

@@ -0,0 +1,2 @@
+(macOS) Fix OpenCV (``cv2``) loader error in generated macOS .app
+bundles, caused by the relocation of package's source .py files.