gh-132661: Disallow Template/str concatenation after PEP 750 spec update

[davepeck]

Following the steering council decision and corresponding update to PEP750, we are removing support for both implicit and explicit Template/str concatenation.

• Issue: Implement PEP 750 – Template Strings #132661

[sobolevn]

Thank you!

[lysnikolaou]

Happy to do this with your input, or happy to hand it off to you!

Happy to help out / review this PR if you wanna take a stab at it. Feel free to reach out if you have any specific questions.

[davepeck]

@lysnikolaou Think this is ready. The only question for me is whether we want to go further with _PyPegen_concatenate_strings().

[sobolevn]

Thank you! Several small nitpicks :)

[lysnikolaou]

Thanks @davepeck for working on this! Looks great in general. Left a few unimportant comments and one more significant one about how to implement this in the parser. Also, we'll need to change ast_unparse.c around https://github.com/python/cpython/blob/main/Python/ast_unparse.c#L715.

[efimov-mikhail]

LGTM

[lysnikolaou]

Looks great and aaalmost there. I have one last thing I missed during my previous reviews.

If I remember correctly, https://github.com/python/cpython/blob/main/Python/codegen.c#L4084-L4093 can be removed as well, because it's only there to handle FormattedValues, which cannot happen anymore.

After that, it's gonna be good to go, promise!

[davepeck]

If I remember correctly, https://github.com/python/cpython/blob/main/Python/codegen.c#L4084-L4093 can be removed as well, because it's only there to handle FormattedValues, which cannot happen anymore.

@lysnikolaou Ah, yes -- thank you. Removed now; tests continue to pass.

(If we prefer, I can replace VISIT() in the else block with a direct ADDOP_LOAD_CONST(). I'd probably add an assert(value->kind == Constant_kind) there, too.)

[lysnikolaou]

Looks good to me! Thanks @davepeck! Great work.

[miss-islington-app]

Thanks @davepeck for the PR, and @lysnikolaou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @davepeck and @lysnikolaou, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker c5e77af131aa0c8832a9ee50c4410731254e4209 3.14

[lysnikolaou]

I can handle tha backport.

[serhiy-storchaka]

Reminder about backporting. @davepeck @lysnikolaou

[encukou]

GH-136901 is a backport of this pull request to the 3.14 branch.