7375 – Regression(2.057): Invalid downcast permitted with derived/aliased template classes

a.d:
----------------
import b;
void main(string[] args)
{
	auto foo = getEleven();
	//auto dummy = cast(Derived!11)foo;
	assert(cast(Derived!22)foo is null);
}
alias DerivedAlias!22 X;
----------------
b.d:
----------------
module b;
Base getEleven()
{
	Base foo = new MoreDerived!11(null);
	return foo;
}
class Base
{
	Base a;
	this(Base a)
	{
		this.a = a;
	}
}
class Derived(int i) : Base
{
	this(Base a)
	{
		super(a);
	}
}
class MoreDerived(int i) : Derived!i
{
	this(Base a)
	{
		super(a);
	}
}
template DerivedAlias(int i)
{
	alias Derived!i DerivedAlias;
}
----------------
On 2.057, the assert fails. (It's fine on 2.056.)
If you uncomment the "dummy" line, the problem goes away (merely creating an alias for Derived!11 does not work). However, that's *not* a general workaround because in order to test what the runtime type is, you have to *already* know *all* the types it might be and attempt to downcast to each of them.

Sorry, I forgot to finish minimizing "b.d". The properly minimized "b.d" is:
--------------------
module b;
Base getEleven()
{
	Base foo = new MoreDerived!11();
	return foo;
}
class Base {}
class Derived(int i) : Base {}
class MoreDerived(int i) : Derived!i {}
template DerivedAlias(int i)
{
	alias Derived!i DerivedAlias;
}
--------------------

A one file version:
-------------------
class A {}
class B(int i) : A {}
class C(int i) : B!i {}
template DerivedAlias(int i)
{
 alias B!i DerivedAlias;
}
alias DerivedAlias!22 X;
void main(string[] args)
{
 A foo = new C!11();
 //auto dummy = cast(B!11)foo;
 assert(cast(B!22)foo is null);
}

The failure definitely happened between 2.056 and 2.057. Anyone care to run the git binary diff thing?

Auch, I found it. In druntime/src/rt/cast_.d, the addition of a name compare saying the classes are the same in _d_isbaseof and _d_isbaseof2.
Not sure what the right fix is.

The culprit:
https://github.com/D-Programming-Language/druntime/commit/5d21d47b5adda97759d15ec0139c0d5fac646971 

I suspected is was that commit. (I remember seeing it when it was committed) Sorry I didn't get around to looking into it earlier.
I think the solution is to do a compare on the full mangled name of the class, but I can't see anywhere it's exposed in the classinfo so it would need to be added.
This should probably be delayed until after the release and the commit reverted.

This was introduced by pull #92
https://github.com/D-Programming-Language/druntime/commits/29f33bfdc0d36484e77ae8f369656720319f22e3.
This added classinfo.name comparison while searching base classes.

https://github.com/D-Programming-Language/druntime/pull/142 

Commits pushed to master at https://github.com/D-Programming-Language/dmd
https://github.com/D-Programming-Language/dmd/commit/3a6c3629f3185c2d65354d1f04c500eb737d49d9
fix Issue 7375 - Regression(2.057): Invalid downcast permitted with derived/aliased template classes
https://github.com/D-Programming-Language/dmd/commit/667ff95c935bc1cf743517b69d2dc421e43f9a51
fix Issue 7375 - Regression(2.057): Invalid downcast permitted with derived/aliased template classes

Commit pushed to dmd-1.x at https://github.com/D-Programming-Language/dmd
https://github.com/D-Programming-Language/dmd/commit/06a33d14f9ad137d86309d40180ca0e60f4edb74
fix Issue 7375 - Regression(2.057): Invalid downcast permitted with derived/aliased template classes

I fixed this in the compiler, not the runtime.

Commit pushed to master at https://github.com/D-Programming-Language/druntime
https://github.com/D-Programming-Language/druntime/commit/b7bdcdce294729e48b56fa5d8feca5aa9a8cc253
Revert "Merge pull request #92 from shoo/fix7020"
This reverts commit 29f33bfdc0d36484e77ae8f369656720319f22e3, reversing
changes made to f11dd3e56476f75804809ecc14da2e65de3f335e.
fixes Issue 7375