ty fails to infer the return type (T) for a generic method whose first parameter is a callable typed with Callable[Concatenate[SelfType, P], T]. In practice this shows up in polars.DataFrame.pipe, where reveal_type(df.pipe(f)) becomes Unknown even when f is fully annotated to return DataFrame.

Polars documents DataFrame.pipe as:

DataFrame.pipe(
    function: Callable[Concatenate[DataFrame, P], T],
    *args: P.args,
    **kwargs: P.kwargs,
) -> T

Reproduction (no third-party deps)

https://play.ty.dev/60c9407f-0310-4b4e-b078-fba3d381f132

from typing import Callable, Concatenate, ParamSpec, TypeVar, reveal_type

P = ParamSpec("P")
T = TypeVar("T")

class DF:
    def pipe(self, function: Callable[Concatenate["DF", P], T], *args: P.args, **kwargs: P.kwargs) -> T:
        return function(self, *args, **kwargs)

def f(df: DF) -> DF:
    return df

reveal_type(DF())          # expected: DF
reveal_type(DF().pipe(f))  # expected: DF; actual (ty): Unknown

Reproduction (real-world: Polars)

import polars as pl
from typing import reveal_type

def f(df: pl.DataFrame) -> pl.DataFrame:
    return df

reveal_type(pl.DataFrame())          # expected: DataFrame
reveal_type(pl.DataFrame().pipe(f))  # expected: DataFrame; actual (ty): Unknown

Support Concatenate special form #1535

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