New semantic analyzer: Various small updates (#6246)

These respond to some review feedback in #6240.

Author: JukkaL

mypy/newsemanal/semanal.py

@@ -2646,7 +2646,7 @@ def analyze_types(self, items: List[Expression]) -> List[Type]:
                 if analyzed is not None:
                     result.append(analyzed)
                 else:
-                    # TODO: Is this the right thing to do?
+                    # TODO: Is this the right thing to do? Or maybe return Optional[List[Type]]?
                     result.append(AnyType(TypeOfAny.from_error))
             except TypeTranslationError:
                 self.fail('Type expected', node)

mypy/newsemanal/semanal_main.py

@@ -40,7 +40,13 @@
 
 
 def semantic_analysis_for_scc(graph: 'Graph', scc: List[str]) -> None:
-    # Assume reachability analysis has already been performed.
+    """Perform semantic analysis for all modules in a SCC (import cycle).
+
+    Assume that reachability analysis has already been performed.
+    """
+    # Note that functions can't define new module-level attributes
+    # using 'global x', since module top levels are fully processed
+    # before functions. This limitation is unlikely to go away soon.
     process_top_levels(graph, scc)
     process_functions(graph, scc)
 

mypy/plugin.py

@@ -182,7 +182,12 @@ def anal_type(self, t: Type, *,
                   allow_unbound_tvars: bool = False,
                   report_invalid_types: bool = True,
                   third_pass: bool = False) -> Optional[Type]:
-        """Analyze an unbound type."""
+        """Analyze an unbound type.
+
+        Return None if the some part of the type is not ready yet (only
+        happens with the new semantic analyzer). In this case the current
+        target being analyzed will be deferred and analyzed again.
+        """
         raise NotImplementedError
 
     @abstractmethod

test-data/unit/check-newsemanal.test

@@ -80,6 +80,15 @@ from b import bad # E: Module 'b' has no attribute 'bad'
 [file b.py]
 from a import bad2 # E: Module 'a' has no attribute 'bad2'
 
+[case testNewAnalyzerTypeAnnotationCycle4]
+# flags: --new-semantic-analyzer
+import b
+[file a.py]
+from b import bad # E: Module 'b' has no attribute 'bad'
+[file b.py]
+# TODO: Could we generate an error here as well?
+from a import bad
+
 [case testNewAnalyzerSimpleFunction]
 # flags: --new-semantic-analyzer
 def f(x: int) -> str: