Fix issue 20431 - Allow a Mixin Type to resolve to an expression

[BorisCarvajal]

It also fix the parsing of mixin(basic type) in __traits(compiles) and using a mixin as an index in array declarations. See the test case.

A side effect is that the next code works now:

alias fun = mixin("(){}");

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20431	minor	Allow a Mixin Type to resolve to an expression where it makes sense

Testing this PR locally

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

dub fetch digger
dub run digger -- build "stable + dmd#10629"

[WalterBright]

Your PR doesn't reference any Bugzilla issue.

Please follow the correct form for subjects that fix bugzilla issues:

fix Issue NNNN title

There's also no explanation of what the worse fix was? A link to it is needed.

It also fix the parsing of mixin(basic type) in __traits(compiles) and using a mixin as an index in array declarations.

Please do not mix multiple issues into one PR.

[BorisCarvajal]

I've filed a new issue with a clear description now.

[MoonlightSentinel]

This introduced a regression: https://issues.dlang.org/show_bug.cgi?id=21074

[BorisCarvajal]

@MoonlightSentinel, thanks for reporting it.

Fix #11458

[MoonlightSentinel]

This PR introduced another regression: https://issues.dlang.org/show_bug.cgi?id=22969