Simplify logic in _ImportVisitor

This is dangerous because I do not fully understand it.
Also, in #106, @MrMino has described a number of cases I think we
do not test for.

My hope is that in the worst case this will lead us to improving our
test cases.

Author: adamtheturtle

pip_check_reqs/common.py

@@ -75,29 +75,18 @@ def visit_ImportFrom(  # noqa: N802, pylint: disable=invalid-name
     def _add_module(self, modname: str, lineno: int) -> None:
         if self._ignore_modules_function(modname):
             return
-        path = None
-        progress = []
-        modpath = None
-        for modname_part in modname.split("."):
-            find_spec_result = importlib.util.find_spec(
-                name=modname_part,
-                package=path,
-            )
-
-            if find_spec_result is None:
-                # The component specified at this point is not installed.
-                break
-
-            modpath = find_spec_result.origin
 
-            # success! we found *something*
-            progress.append(modname_part)
-
-        if modpath is None:
-            # the module doesn't actually appear to exist on disk
+        find_spec_result = importlib.util.find_spec(
+            name=modname.split(".")[0],
+        )
+        if find_spec_result is None:
+            # The component specified at this point is not installed.
             return
 
-        modname = ".".join(progress)
+        modpath = find_spec_result.origin
+        assert modpath is not None
+        modname = find_spec_result.name
+
         if modname not in self._modules:
             self._modules[modname] = FoundModule(
                 modname=modname,

tests/test_common.py

@@ -45,7 +45,8 @@ def test_found_module() -> None:
         ("from pathlib import Path", ["pathlib"]),
         ("from string import hexdigits", ["string"]),
         ("import urllib.request", ["urllib"]),
-        ("import spam", []),  # don't break because bad programmer
+        # don't break because bad programmer imported the file we are in
+        ("import spam", []),
         ("from .foo import bar", []),  # don't break on relative imports
         ("from . import baz", []),
     ],