Fix Issue 18970 - DMD segfault due to opDispatch

[wilzbach]

The error doesn't get displayed, because for opDispatch gagging is activated:

dmd/src/dmd/typesem.d

Lines 3056 to 3063 in ecc8d82

	/* opDispatch, which doesn't need IFTI, may occur instantiate error.
	* e.g.
	* template opDispatch(name) if (isValid!name) { ... }
	*/
	uint errors = gagError ? global.startGagging() : 0;
	e = dti.semanticY(sc, 0);
	if (gagError && global.endGagging(errors))
	e = null;

(gets called from TypeStruct::dotExp(e = 'S()', ident = 'y') via semanticY and resolveUFCS)

[dlang-bot]

Thanks for your pull request, @wilzbach!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	18970	critical	DMD segfault due to opDispatch

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#8354"

[UplinkCoder]

@wilzbach gagging needs to be active for opDispatch, since it's entirely speculative compilation.
you should be able to fix the segfault without turning off gagging.
The key to success here would be inserting an ErrorExp instead of leaving this being null.
At least this is what I think taking a short glance at 5 am.

[wilzbach]

Oh it's working (there was just an accidental line mismatch error due to rebasing).
Anyhow, I was trying to point out why the error message added here isn't shown.

The SemaphoreCI error is unrelated.