fix: longest prefix for nested modules

Author: changhoetyng

mypy/semanal.py

@@ -6409,35 +6409,43 @@ def lookup_fully_qualified_or_none(self, fullname: str) -> SymbolTableNode | Non
         #       we might keep the module level only lookup for thing like 'builtins.int').
         assert "." in fullname
 
-        module, name = fullname.rsplit(".", maxsplit=1)
-
-        # The reason for this is that we want to be able to handle cases such as importlib.machinery
-        if module not in self.modules:
-            # Check if there's nested module A.B.C
-            splitted = fullname.rsplit(".")
-            module, names = splitted[0], splitted[1:]
-            # If module still not in modules, return None
-            if module not in self.modules:
-                return None
-            filenode = self.modules[module]
-            result = filenode.names.get(names[0])
+        splitted_modules = fullname.rsplit(".")
+        names = []
 
-            if result is None and self.is_incomplete_namespace(module):
-                # TODO: More explicit handling of incomplete refs?
-                self.record_incomplete_ref()
+        while splitted_modules and ".".join(splitted_modules) not in self.modules:
+            '''
+            Try to find the module in the modules dictionary.
 
-            for part in names[1:]:
-                if result is not None and isinstance(result.node, TypeInfo):
-                    result = result.node.names.get(part)
-                else:
-                    return None
-            return result
+            If the module is not found, pop the last element of the splitted list and append it to the names list.
+
+            This is to find the longest prefix of the module name that is in the modules dictionary.
+            '''
+            names.append(splitted_modules.pop())
 
+        if not splitted_modules or not names:
+            '''
+            If no module or name is found, return None.
+            '''
+            return None
+
+        '''
+        Reverse the names list to get the correct order of names.
+        '''
+        names.reverse()
+
+        module = ".".join(splitted_modules)
         filenode = self.modules[module]
-        result = filenode.names.get(name)
+        result = filenode.names.get(names[0])
+
         if result is None and self.is_incomplete_namespace(module):
             # TODO: More explicit handling of incomplete refs?
             self.record_incomplete_ref()
+
+        for part in names[1:]:
+            if result is not None and isinstance(result.node, TypeInfo):
+                result = result.node.names.get(part)
+            else:
+                return None
         return result
 
     def object_type(self) -> Instance:

test-data/unit/check-python312.test

@@ -1933,3 +1933,19 @@ class Z:
 
 a = Z.A()
 v = a.f
+
+[case testPEP695MultipleNestedGenericClass5]
+# flags: --enable-incomplete-feature=NewGenericSyntax
+from a.b.c import d
+x: d.D.E.F.G[int]
+x.g('a') # E: Argument 1 to "g" of "G" has incompatible type "str"; expected "int"
+reveal_type(x)  # N: Revealed type is "a.b.c.d.D.E.F.G[builtins.int]"
+reveal_type(d.D.E.F.d)  # N: Revealed type is "a.b.c.d.D.E.F.G[builtins.str]"
+
+[file a/b/c/d.py]
+class D:
+    class E:
+        class F:
+            class G[Q]:
+                def g(self, x: Q): ...
+            d: G[str]