python / python/mypy

Plugin's get_type_analyze_hook is not used for Annotated type in type alias or generic specialization

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Description

Bug Report

Mypy doesn't use plugin's get_type_analyze_hook for Annotated type used in type alias or generic specialization. However, the hook is used for custom types (not Annotated) used in these contexts, and it's also called for Annotated used in other contexts.

To Reproduce

plugin.py

from typing import Callable

from mypy.plugin import AnalyzeTypeContext, Plugin
from mypy.types import NoneType, Type

def plugin(version: str):
    return MyPlugin

class MyPlugin(Plugin):
    def get_type_analyze_hook(self, fullname: str) -> Callable[[AnalyzeTypeContext], Type] | None:
        if fullname in {'typing.Annotated', 'typing_extensions.Annotated'}:
            return _type_analyze
        return None

def _type_analyze(ctx: AnalyzeTypeContext) -> Type:
    ctx.api.note('Analyzing type of Annotated[...]', ctx.context)
    return NoneType()  # for the sake of example

module.py

from typing import Annotated, Generic, TypeAlias, TypeVar, reveal_type

AnnotatedTA: TypeAlias = Annotated[dict, None]
typed_with_alias: AnnotatedTA
reveal_type(typed_with_alias)  # Revealed type is "builtins.dict[Any, Any]"

typed_directly: Annotated[dict, None]  # Analyzing type of Annotated[...]
reveal_type(typed_directly)  # Revealed type is "None", as expected


T = TypeVar('T')

class GenericType(Generic[T]):
    dummy: T

class Specialization(GenericType[Annotated[dict, None]]):
    ...

reveal_type(Specialization().dummy)  # Revealed type is "builtins.dict[Any, Any]"

Expected Behavior

All revealed types are None as requested by _type_analyze hook

Actual Behavior

Only directly typed variable typed_directly has the type requested by plugin

Your Environment

  • Mypy version used: 1.10.1
  • Mypy command-line flags: none
  • Mypy configuration options from mypy.ini (and other config files): plugins = plugin.py
  • Python version used: 3.8, 3.12

Background

I'm writing a plugin which generates TypedDictType for Annotated[dict, ...] annotations based on some external configuration files. The arguments to Annotated are string literals, so I can't really use generics. In runtime these are just normal dicts.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the plugin.py and module.py reproducer with the reported Python and mypy versions, then trace type analysis for Annotated in direct use, the TypeAlias, and generic specialization. Done means the hook is invoked in all three cases and each reveal_type reports None as requested by _type_analyze.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
48/100

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