Incorrect syntax highlighting for method calls in subclassing parameters

[jonathandung]

Environment data

• Pylance version: 2026.2.100
• OS and version: Microsoft Windows Version 25H2 (OS Build 26200.846)
• Python version: Python 3.14.0 (tags/v3.14.0:ebf955d, Oct 7 2025, 10:15:03)

Code Snippet

from typing import Any
class B:
    def __init_subclass__(cls, *, foo, bar): print(f'foo: {foo}, bar: {bar}', file=bar) # a base class with custom __init_subclass__ taking some keyword parameters
def f(x) -> Any: return x # strip away type information
reveal_type(f(1)) # revealed type is 'Any'
class A(B, foo=f('').lower, bar='bar.txt'): ...

Expected behavior

Below is from the perspective of dark mode.

lower, a method of strings, correctly shows as the same colour (yellow) as methods and functions in other contexts when the function f is not applied. However, after the type is cast to Any, lower is no longer an attribute of known type. Therefore, it should not be highlighted (white), or in the worst case highlighted with the colour for attributes on objects (light blue).

Actual behavior

lower is highlighted as green, the colour for classes. It was probably treated as a base class due to its location. This should be special-cased.

[github-actions]

Hi @jonathandung, I'm an AI Support assistant here to help with your issue. While the team reviews your request, I wanted to provide some possible tips and documentation that might help you in the meantime.

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Similar Issues (FYI only, not solutions)

The following issues may or may not be related to your report. They are provided for reference only, as they may describe similar symptoms, affect the same feature, or address related concerns, but may not be the same issue.

• Signature help highlights / and * as if they were actual parameters – Signature help highlights / and * as if they were actual parameters #3507

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[rchiodo]

Ah this is a textmate issue. It thinks '.lower' is a class. It's not semantic tokens so Pylance isn't actually providing this value.

Pylance is providing no token.

[jonathandung]

I thought textmate was for MacOS only, but I'm experiencing the issue on Windows. Sorry if that's wrong.

[rchiodo]

VS code has two paths for colorization. Textmate based grammars are the default. Semantic tokens can enhance that. Pylance provides both but the Textmate grammar is really just a port of this one:

https://github.com/microsoft/vscode-textmate/blob/main/test-cases/themes/syntaxes/MagicPython.tmLanguage.json

I think the only way to fix this would be to provide a semantic token for this special case that forces 'local' to any. I don't see how a regex can possibly get the color right.

[heejaechang]

@jonathandung Thanks for the report. This looks like a limitation of the legacy TextMate-based syntax coloring used by VS Code. That layer is regex-based, so it does not have AST context and cannot reliably distinguish a real inherited class reference from an expression like foo=f('').lower inside the class base list.

In general, we try to let TextMate handle syntactic coloring and keep Pylance focused on semantic coloring. This is not easy to fix in the current TextMate-based system.

A robust fix here would likely require tree-sitter based syntax coloring rather than additional regex rules, so this is probably something to revisit once that becomes the default path in VS Code.

[heejaechang]

Retained repro workspace: https://github.com/heejaechang/pylance-repro/tree/main/pylance-issues/7997