Fix 21590 - assignment inside assert accepted for -checkaction=context

[MoonlightSentinel]

The rewrite introduced a temporary which hid the assignment inside of
assert(...) and hence prevented the error.

The fix is to omit the additional temporary for (Bin)AssignExp and use
the assigned variable directly. The temporary is unecessary anyways
and the following semantic analysis will raise an appropriate error.

[dlang-bot]

Thanks for your pull request and interest in making D better, @MoonlightSentinel! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21590	regression	assignment inside assert accepted if -checkaction=context is given

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 "stable + dmd#12165"

[Geod24]

This doesn't detect other kind of assignments, such as CatAssignExp, does it ?

[MoonlightSentinel]

This doesn't detect other kind of assignments, such as CatAssignExp, does it ?

Fixed. But there is no error for those expressions at the moment (regardless of -checkaction=context)

[BorisCarvajal]

Copy toBoolean() function from AssignExp to BinAssignExp, maybe that will work.

[MoonlightSentinel]

Copy toBoolean() function from AssignExp to BinAssignExp, maybe that will work.

It does, but it also breaks a lot of code.

Boolean conversion for assignments is rejected because it's most likely a typo ( = vs ==), but this reasoning doe not apply to binary assignments (e.g. +=).

[Geod24]

LGTM