POC: automatically move scope array literals to the stack

[dkorpel]

See #16888 (comment)

Just a proof of concept, I don't think this is worth merging at this stage. Maybe under -preview=dip1000 only.

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[Geod24]

I assume you will make scope foo = [...] @nogc ?

[dkorpel]

I assume you will make scope foo = [...] @nogc ?

If this is actually worth pursuing, yes. It's non-trivial because currently, @nogc is eagerly checked on each expression, while in this case, an array literal expression can only be checked at the end of the function.

[dkorpel]

That patch could introduce dangling pointers in @safe code. -preview=dip1000 is required to verify the stack-allocated array literal doesn't escape.

-betterC simply disables language features that require druntime, it does not negate @safe or change language semantics in other ways, so checking for global.params.betterC likely isn't the right answer here.