bpo-40715: Reject dict unpacking on dict comprehensions

[isidentical]

https://bugs.python.org/issue40715

[lysnikolaou]

Suggestion for being consistent with things like starred_expression (feel free to ignore): Rename kvpair to double_starred_kvpair and simple_kvpair to plain kvpair. What do you think?

[pablogsal]

@isidentical You need to rebase and regenerate the parser

[lysnikolaou]

Also, if we want to be completely compatible with the old parser, the error caret should point to the opening brace:

╰─ cat t.py
{**{} for a in [1]}
╰─ ./python.exe -X oldparser t.py
  File "/Users/lysnikolaou/Repositories/cpython/t.py", line 1
    {**{} for a in [1]}
    ^
SyntaxError: dict unpacking cannot be used in dict comprehension

[isidentical]

Also, if we want to be completely compatible with the old parser, the error caret should point to the opening brace:

I thought it should be same with single starred expressions

 $ python t.py
  File "t.py", line 1
    [*[] for a in b]
     ^
SyntaxError: iterable unpacking cannot be used in comprehension

[lysnikolaou]

Also, if we want to be completely compatible with the old parser, the error caret should point to the opening brace:

I thought it should be same with single starred expressions

 $ python t.py
  File "t.py", line 1
    [*[] for a in b]
     ^
SyntaxError: iterable unpacking cannot be used in comprehension

Yup, I find that kind of weird as well!

[pablogsal]

Also, if we want to be completely compatible with the old parser, the error caret should point to the opening brace:

Yeah, I think the old parser is the one should point to the **, but I don't think we need to make them match. I personally prefer that it points to the invalid token: the ** which is also consistent with starred expressions.

[lysnikolaou]

Also, if we want to be completely compatible with the old parser, the error caret should point to the opening brace:

Yeah, I think the old parser is the one should point to the **, but I don't think we need to make them match. I personally prefer that it points to the invalid token: the ** which is also consistent with starred expressions.

If we've got no problem with showing to another token than the one the old parsers shows to, then no doubt, the '**' is the right one.

[lysnikolaou]

LGTM! 🎉

[miss-islington]

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

[bedevere-bot]

GH-20303 is a backport of this pull request to the 3.9 branch.