bpo-40334: Produce better error messages for non-parenthesized genexps

[lysnikolaou]

The error message, generated for non-parenthesized generator expression
in function calls, was still the generic invalid syntax, when the
generator expression wasn't appearing as the first argument in the call.
Now, even on inputs like f(a, b, c for c in d, e), the correct error
message gets produced.

PS Last one with this bpo number. Promise!

https://bugs.python.org/issue40334

[pablogsal]

Humm, there are still some mistmatches. For instance:

>>> f(x=3,x for x in L,)
  File "<stdin>", line 1
    f(x=3,x for x in L,)
            ^
SyntaxError: positional argument follows keyword argument

with the old parser:

>>> f(x=3,x for x in L,)
  File "<stdin>", line 1
SyntaxError: Generator expression must be parenthesized

[lysnikolaou]

Humm, there are still some mistmatches. For instance:

>>> f(x=3,x for x in L,)
  File "<stdin>", line 1
    f(x=3,x for x in L,)
            ^
SyntaxError: positional argument follows keyword argument

with the old parser:

>>> f(x=3,x for x in L,)
  File "<stdin>", line 1
SyntaxError: Generator expression must be parenthesized

Fixed in ed64876.

[lysnikolaou]

@pablogsal Would you be able to give this another review?

[pablogsal]

@pablogsal Would you be able to give this another review?

Absolutely, will try to review this tonight :)

[lysnikolaou]

@pablogsal Would you be able to give this another review?

Absolutely, will try to review this tonight :)

No rush, whenever you find the time.

[pablogsal]

LGTM

I have been playing with some edge cases and it behaves as expected 🎉

[miss-islington]

Thanks @lysnikolaou for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

[bedevere-bot]

GH-20307 is a backport of this pull request to the 3.9 branch.

[lysnikolaou]

Thanks thanks!