Fix issue 18439: Remove attributes applied to hidden lambda in static foreach

[looked-at-me]

I think someone said they were making a patch that'd "fix" this issue, but it has been close to a year now with no "fix" in sight and I keep bumping up against this bug. Would rather have a simple imperfect 5 line patch than let perfection be the enemy of sanity.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	18439	major	Error: cannot use operator ~= in @nogc delegate 'main.test.__lambda1'

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#10851"

[wilzbach]

If stable is targeted it could still be part of the 2.091 release.

[tgehr]

Like I said last time, there should be a comment in the code that this is a temporary hack that will be removed once the mess with attributes is sorted out. I'm not opposed to temporarily pulling this, but I had explained how to fix this the proper way and that fix requires way fewer changes to the source code, so I don't really buy the 5-line-change argument.

[tgehr]

https://github.com/dlang/dmd/pull/9922

[looked-at-me]

Pure will be a bit more involved fix due to the hacky use of lambdas in the implementation and the way nested lambda's infer their purity. It'll just have to be @nogc for now. The error message for pure is less cryptic.

[BorisCarvajal]

The test case no longer triggers the error since v2.094 because numeric ranges no longer use CTFE, but using opApply (or a range interface) does it, of course.

@nogc:
struct S
{
    int opApply(scope int delegate(int) dg) { return 0;}
}
void test() {
    static foreach(i; S()) {} // @nogc
}