Add missing modules to packages_distributions

[FFY00]

This now considers:

• Modules that don't have the .py prefix (eg. native modules, .pyc-only modules)
• Namespace packages without any .py files inside

Which I think should be all possible modules, right?

Fix #428

[FFY00]

Edge case I found: empty namespace packages, which are still importable, can't ever be reported with the current abstractions. I don't think this is a big issue though, https://github.com/pypa/installer also does not support creating empty directories, so people trying to ship packages containing such thing will likely get trouble trying to install them in the first place.

[jherland]

I wonder if this adds the metadata directories into the output of packages_distributions() as import names. After this was merged, I'm seeing entries like these returned from packages_distributions():

 'black-23.1.0.dist-info': ['black'],
 'filelock-3.10.0.dist-info': ['filelock'],
 'iniconfig-2.0.0.dist-info': ['iniconfig'],
 'more_itertools-9.1.0.dist-info': ['more-itertools'],
 'typing_extensions-4.5.0.dist-info': ['typing_extensions'],

IMHO, these should never occur here, as they are not importable modules.

[jherland]

Confirmed by applying this diff to the test added in this PR; the important stuff is in the last 4 lines, but I first needed to change the existing dummy module names into valid import names (== valid Python identifiers):

diff --git a/tests/test_main.py b/tests/test_main.py
index 1636779..d448e6c 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -336,10 +336,10 @@ class PackagesDistributionsTest(
                         Version: 1.0.0
                     """,
                     'RECORD': ''.join(
-                        f'{i}-top-level{suffix},,\n'
-                        f'{i}-in-namespace/mod{suffix},,\n'
-                        f'{i}-in-package/__init__.py,,\n'
-                        f'{i}-in-package/mod{suffix},,\n'
+                        f'top_level_{i}{suffix},,\n'
+                        f'in_namespace_{i}/mod{suffix},,\n'
+                        f'in_package_{i}/__init__.py,,\n'
+                        f'in_package_{i}/mod{suffix},,\n'
                         for i, suffix in enumerate(suffixes)
                     ),
                 },
@@ -350,6 +350,11 @@ class PackagesDistributionsTest(
         distributions = packages_distributions()
 
         for i in range(len(suffixes)):
-            assert distributions[f'{i}-top-level'] == ['all_distributions']
-            assert distributions[f'{i}-in-namespace'] == ['all_distributions']
-            assert distributions[f'{i}-in-package'] == ['all_distributions']
+            assert distributions[f'top_level_{i}'] == ['all_distributions']
+            assert distributions[f'in_namespace_{i}'] == ['all_distributions']
+            assert distributions[f'in_package_{i}'] == ['all_distributions']
+
+        # All keys returned from packages_distributions() should be valid import
+        # names, which means that they must _at least_ be valid identifiers:
+        for import_name in distributions.keys():
+            assert import_name.isidentifier(), import_name

[jherland]

I wonder if the final if f.suffix == ".py" clause in the set comprehension that was lost in this PR should instead be replaced with something like if f.suffix in importlib.machinery.all_suffixes()? Otherwise it seems we accept any first-level directories that are part of .files paths, even those that do not contain any packages/modules.

[ucodery]

I came here to say the same thing as @jherland. The introduction of package.version.dist-info has caused problems with one of my apps that started finding "extra" import targets. It's not only metadata dirs, this change also adds .. as a key in some cases, presumably for any distribution that ships an executable and has files like ../../../bin/tool associated with it.

To reproduce:

1. create a new venv
2. pip install importlib_metadata==6.1 wheel

$ python -m pip list
Package            Version
------------------ -------
importlib-metadata 6.1.0
pip                21.2.3
setuptools         57.4.0
wheel              0.40.0
zipp               3.15.0

$ python -c "import importlib_metadata;print(importlib_metadata.packages_distributions())"
{'_distutils_hack': ['setuptools'], 'pkg_resources': ['setuptools'], 'setuptools': ['setuptools'], 'zipp': ['zipp'], 'wheel-0.40.0.dist-info': ['wheel'], 'wheel': ['wheel'], '..': ['wheel'], 'pip': ['pip'], 'importlib_metadata': ['importlib-metadata']}