Improve `class A[]: ...` syntax error message

[sobolevn]

Feature or enhancement

Right now it will generate this default error:

>>> class A[]: ...
  File "<stdin>", line 1
    class A[]: ...
            ^
SyntaxError: invalid syntax
>>> def some[](arg: int) -> None: ...
  File "<stdin>", line 1
    def some[](arg: int) -> None: ...
            ^
SyntaxError: expected '('
>>> type Alias[] = int
  File "<stdin>", line 1
    type Alias[] = int
               ^
SyntaxError: invalid syntax

I propose to change it to:

>>> class A[]:
  File "<stdin>", line 1
    class A[]:
            ^
SyntaxError: At least one type variable definition is expected
>>> def some[](arg: int) -> None: ...
  File "<stdin>", line 1
    def some[](arg: int) -> None: ...
             ^
SyntaxError: At least one type variable definition is expected

>>> type Alias[] = int
  File "<stdin>", line 1
    type Alias[] = int
               ^
SyntaxError: At least one type variable definition is expected

I have a PR ready.

Linked PRs

• gh-118090: Improve error message for empty type param brackets #118091

[wookie184]

It looks like this was fixed, can this be closed @sobolevn?