fix #20508 escaping sliced stack arrays not detected

[WalterBright]

[dlang-bot]

Thanks for your pull request, @WalterBright!

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Testing this PR locally

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dub run digger -- build "master + dmd#22207"

[WalterBright]

m_lock.performLocked!({ m_streamWSize[sid] = newWin; });

  | ^   | ../.dub/packages/vibe-http/1.3.1/vibe-http/source/vibe/http/internal/http2/exchange.d(84,9): Error: returning scope variable res is not allowed in a @safe function

Anyone know anything about this code?

[WalterBright]

@dkorpel may need to enable this with an edition

[dkorpel]

may need to enable this with an edition

If you guard the code with if (sc.hasEdition(Edition.v2024)) it will only take effect from that edition onwards.

[dkorpel]

Anyone know anything about this code?

https://github.com/vibe-d/vibe-http/blob/94e4d1fe6c5eace1de38456a79040c5e94b422e7/source/vibe/http/internal/http2/exchange.d#L55

It looks like it incorrectly marks the allocator parameter as scope instead of return scope in a @safe function, which should be an error but it passes because it's not compiled with -preview=dip1000. This PR restricts returning scope variables even without dip1000, so it now breaks.

[WalterBright]

@dkorpel I added the edition check, thanks!

[WalterBright]

This is ready to go.