Early exit error messages are unsustainable

[Ethan]

SOOOOOO

Since not many liked the idea of static assert behaving correctly 
(note for reference that C++'s static_assert will not stop 
compilation in at least MSVC and will give you all the error 
information you need), here's another example that's currently 
driving me up the wall.

Error: template instance `AliasSeq!( ... )` recursive template 
expansion

This one's the result of trying to compile my code in LDC. 
Symbols omitted because they're not important.

What is the important part? As a part of dealing with "recursive 
template expansion" last time the compiler didn't want to give me 
information, I determined that an AliasSeq will give that error 
if something fails to compile.

While tracking down another error, I discovered that LDC has 
issues with cross-module visibility and alias this. This code 
compiles just fine in online compiler testers:

struct Something
{
     enum Val = 5;
     int dummy;
}

struct SomethingElse
{
     Something derp;
     alias derp this;
}

pragma( msg, SomethingElse.Val.stringof );

But put it across modules (and, in my case, template the 
equivalent of SomethingElse) and things start going wrong in LDC.

Which leads me to the recursive expansion. Because whatever's 
going on wherever in my code, the compiler knows there's a 
problem and is refusing to tell me.

This code should have been compiling hours ago, and I should have 
been uploading this binary not long after.

These instances of the compiler stopping have cost me too much 
time. Counter arguments to this are just plain incorrect. Any 
given compiler *needs* to tell the user *why it's not compiling 
code*.

As it stands, it's a crapshoot hand-auditing about 10,000 lines 
of heavily templated D code right now trying to find out what the 
actual problem is. This is neither a fun nor entertaining nor 
productive use of my time.