checker: error on empty integer range in for-in loop

[arshalaromal]

This PR adds a semantic check to prevent empty hardcoded integer ranges (e.g., for i in 4 .. 2) in for ... in loops.

Because V ranges are exclusive (start .. end), a loop where start >= end will never execute. Previously, this would silently compile and skip the loop entirely. This change aligns with V's strictness by catching this unreachable code and potential typo at compile time with a hard error.

Resolves #27720

Tests

Added for_in_empty_range_err.vv and for_in_empty_range_err.out to vlib/v/checker/tests/ to cover this specific compiler error.

[GGRei]

@codex review

[chatgpt-codex-connector]

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Reviewed commit: 665218db47

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[GGRei]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: a971c98cdb

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Codex Review: Didn't find any major issues. Keep them coming!

Reviewed commit: 28adf68b1d

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[GGRei]

Ok for me its good now.

[arshalaromal]

I've updated the test expectation to 2:14 as requested

[GGRei]

Sorry, I gave you the wrong instruction. I ran the targeted test before running v fmt on the .vv file. v fmt changes the indentation to tabs, making 2:11 the correct position. I retested it and the test passes with 2:11. Please just drop your latest commit and make sure to run v fmt on vlib/v/checker/tests/for_in_empty_range_err.vv.

Thanks!

[GGRei]

Your latest commit correctly restored 2:11, but it accidentally added cmd/tools/vbug-report-send.lock and the relevant files are still not formatted. Please remove the lock file and run v fmt on vlib/v/checker/for.v and vlib/v/checker/tests/for_in_empty_range_err.vv.

Thanks :)

[arshalaromal]

i am sorry, is it okay now?

[GGRei]

On the current HEAD, these two files are still not vfmt'ed for me:

vlib/v/checker/for.v
vlib/v/checker/tests/for_in_empty_range_err.vv

[arshalaromal]

Ah, my bad..
Fixed the formatting.
Thanks for the patience and for pointing it out.

[GGRei]

Thanks for your contribution!

[JalonSolov]

If you run v git-fmt-hook install, it will install a pre-commit hook that will format your files before they are committed, so when they are pushed you don't have to worry about it.

[arshalaromal]

I noticed the CI failed on generic_fn_short_syntax_struct_param_test.v. I reproduced the error locally, but then I switched to the master branch and ran the test there, and it fails with the exact same error (unknown struct T). It looks like this is an existing issue on master and unrelated to my range checker changes.

[GGRei]

Yes, at first glance, the CI errors didn’t seem to come from your PR. I can see that Alex patched all of that recently as well. You did the right thing by rebasing onto the upstream branch to check the CI again. In any case, I can’t merge your work myself here, @medvednikov is the one who gives the final approval. :)

[JalonSolov]

Everything looks good for this. The CI failures do appear to be unrelated.