Better message for invalid types like (int, str)

[JukkaL]

The error message "Invalid tuple literal type" isn't very helpful if a user writes (int, str) instead of Tuple[int, str].

Example:

from typing import List

def f():
    # type: () -> (int, str)   # Invalid tuple literal type
    return (1, 'x')

A better message could be something like this:

program.py:3: error: Syntax error in type annotation
program.py:3:note: Suggestion: Use "Tuple[T1, ..., Tn]" instead of "(T1, ..., Tn)"

#4172 is closely related.

[elliott-beach]

Interested. Are you suggesting literally (T1, ..., Tn) or substituting in the types values used, as in, (int, str) in the error message? I think the later makes more sense, if slightly more complex to implement.

[JukkaL]

Are you suggesting literally (T1, ..., Tn) or substituting in the types values used, as in, (int, str) in the error message? I think the later makes more sense, if slightly more complex to implement.

Just literal (T1, ..., Tn) (or something similar) would be enough.

[Hnasar]

Came across this today when I accidentally had:

def foo(
    arg1,  # type: int,
    arg2,  # type: str
):  # type (...) -> None
    pass

The lint was on the first line of the function definition, def foo, but the problem was an errant comma on arg1.

[emmatyping]

@Hnasar that is technically #4172, but these are, as Jukka said previously, closely related.