Fix Issue 16635 - Alias this for implicit conversion to "ref const(typeof(this))" causes dmd to segfault

[BorisCarvajal]

Types att1 and att2 are used to detect a recursive alias this, they are compared to the next alias this type to stop the recursion, however, it's done using a pointer comparison that it will fail if types are equal but have different type qualifiers.

Fix: Do not take into account type qualifiers.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	16635	normal	Alias this for implicit conversion to "ref const(typeof(this))" causes dmd to segfault

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#12161"

[RazvanN7]

With this patch, what happens if byRef and opBinary are marked as immutable? Does the compilation still fail?

[BorisCarvajal]

Does the compilation still fail?

It doesn't fail now, well the first test inside traits(compiles) is not working because no '+' overload.

With this patch, what happens if byRef and opBinary are marked as immutable?

(spec:1) ../test/compilable/test16635.d(46): Error: `immutable` method `test16635.Vector2.byRef` is not callable using a mutable object
../test/compilable/test16635.d(46): Error: incompatible types for `(a) + (Vector2(cast(float)5, cast(float)6))`: both operands are of type `Vector2`

Error message sucks because many are gagged (immutable opBinary fails too without an explicit line) but that's typical of dmd.