Plugin api named_type() is ambiguous and inconsistent and broken #6578
Description
The plugin API defines two different interfaces (TypeAnalyzerPluginInterface and SemanticAnalyzerPluginInterface) that each define a method named_type(). These look almost identical, but looks are deceptive.
First, the specified signatures differ subtly:
- The second argument to SemanticAnalyzerPluginInterface.named_type() is optional, while for TypeAnalyzerPluginInterface.named_type() is is mandatory.
- Also the first argument name differs (qualified_name vs. plain name).
Second, the implementations differ:
- The semantic analyzer (in semanal.py) starts the lookup in the local namespace, then globals, then builtins.
- The type checker (in checker.py) has two different strategies: if there's no dot in the name, it starts in globals, then builtins; but if there's a dot, it starts in the table of modules (i.e. the current scope doesn't enter into it).
Third, the type checker's named_type() implementation doesn't actually take a list of type arguments at all -- it's a method with only one argument, the name to look up. It always fills in all type parameters with Any. (It looks like the method we want here is named_generic_type().)
Fourth, apparently mypy's own type checking doesn't catch the discrepancy between the implemented spec (only a name) and the interface spec (name + args).