Quality of errors in DMD

[Ethan Watson via Digitalmars-d]

Can we have a serious discussion in here about the quality of DMD 
errors?

I've been alternately a dog chasing its own tail, and a dog 
barking at a fire hydrant, chasing down errors deep in templated 
and mixin code over the last day. This has resulted in manually 
reducing templates and mixins by hand until I get to the root of 
the problem, which then results in submitting a bug and devising 
an ugly workaround.

And then I get this one in some code:

Assertion failure: '0' on line 1492 in file 'glue.c'

The problem ended up being that a symbol tucked away in a 
template that itself was tucked away in a template was undefined, 
but it couldn't tell me that. Rather, it just assert(0)'d and 
terminated. Rather less helpfully, the only meaningful 
information it could give me at the assert point (Could it add to 
it further down the stack? Maybe?) was defined out because DMD 
wasn't in a debug build.

Honestly, I find stuff like this in a compiler unacceptable. 
Using assert(0) as shorthand for an unexpected error is all fine 
and dandy until you put your product in the hands of the masses 
and they expect your program to at least give you some idea of 
what was going wrong rather than just crashing out in flames.

So just for fun, I searched DMD for all instances of assert(0) in 
the code base.

830 matches in DMD 2.070.2.

That's 830 possible places where the compiler will give the user 
virtually no help to track down what (if anything) they did wrong.

DMD certainly isn't the only compiler guilty of this. The .NET 
compiler gives precisely no useful information if it encounters 
SSE types in C++ headers for example. But compared to MSVC, I've 
found the error reporting of DMD to be severely lacking. In most 
cases with MSVC, I have an error code that I can google for which 
is (sometimes) thoroughly documented. And thanks to being a 
widely used product, Stack Overflow usually gives me results that 
I can use in my sleuthing.

I know I'm also seeing more errors than most because I'm doing 
the kind of code most people don't do. But I'm certainly of the 
opinion that searching for a compiler error code is far easier 
than trying to trick google in to matching the text of my error 
message.