Fix caching of PEP 561 namespace packages with missing submodules

Fixes #12232

Another "fail every 2nd run" bug

Author: hauntsaninja

mypy/build.py

@@ -736,14 +736,6 @@ def correct_rel_imp(imp: Union[ImportFrom, ImportAll]) -> str:
                     pri = import_priority(imp, PRI_MED)
                     ancestor_pri = import_priority(imp, PRI_LOW)
                     for id, _ in imp.ids:
-                        # We append the target (e.g. foo.bar.baz)
-                        # before the ancestors (e.g. foo and foo.bar)
-                        # so that, if FindModuleCache finds the target
-                        # module in a package marked with py.typed
-                        # underneath a namespace package installed in
-                        # site-packages, (gasp), that cache's
-                        # knowledge of the ancestors can be primed
-                        # when it is asked to find the target.
                         res.append((pri, id, imp.line))
                         ancestor_parts = id.split(".")[:-1]
                         ancestors = []
@@ -768,14 +760,17 @@ def correct_rel_imp(imp: Union[ImportFrom, ImportAll]) -> str:
                     # if all of the imports are submodules, do the import at a lower
                     # priority.
                     pri = import_priority(imp, PRI_HIGH if not all_are_submodules else PRI_LOW)
-                    # The imported module goes in after the
-                    # submodules, for the same namespace related
-                    # reasons discussed in the Import case.
                     res.append((pri, cur_id, imp.line))
                 elif isinstance(imp, ImportAll):
                     pri = import_priority(imp, PRI_HIGH)
                     res.append((pri, correct_rel_imp(imp), imp.line))
 
+        # Ensure that foo.bar.baz is always before foo.bar and foo
+        # This ensures that if FindModuleCache finds a module in a package marked with py.typed
+        # underneath a namespace package installed in site-packages, (gasp), that cache's knowledge
+        # of the ancestors (FindModuleCache.ns_ancestors) is primed when it is asked to find the
+        # parent.
+        res.sort(key=lambda x: -len(x[1]))
         return res
 
     def is_module(self, id: str) -> bool:

test-data/unit/pep561.test

@@ -222,3 +222,13 @@ b.bf(1)
 [out]
 testNamespacePkgWStubsWithNamespacePackagesFlag.py:7: error: Argument 1 to "bf" has incompatible type "int"; expected "bool"
 testNamespacePkgWStubsWithNamespacePackagesFlag.py:8: error: Argument 1 to "bf" has incompatible type "int"; expected "bool"
+
+
+[case testTypedPkgNamespaceRegFromImportTwiceMissing]
+# pkgs: typedpkg_ns_a
+from typedpkg_ns import b  # type: ignore
+from typedpkg_ns import a
+-- dummy should trigger a second iteration
+[file dummy.py.2]
+[out]
+[out2]