Improving assert-printing in DMD

[Andrei Alexandrescu via Digitalmars-d]

On 09/29/2015 11:45 PM, deadalnix wrote:
> On Tuesday, 29 September 2015 at 21:02:42 UTC, Nordlöw wrote:
>> As a follow-up to
>>
>> https://github.com/D-Programming-Language/phobos/pull/3207#issuecomment-144073495
>>
>>
>> I starting digging in DMD for logic controlling behaviour of assert(),
>> especially whether it's possible to add automatic printing of `lhs`
>> and `rhs` upon assertion failure if `AssertExp` is a binary expression
>> say `lhs == rhs`.
>>
>> After grepping for `AssertExp` the only possible place I could think
>> of was
>>
>> ToElemVisitor::visit(AssertExp *ae)
>>
>> inside
>>
>> elem *toElem(Expression *e, IRState *irs)
>>
>> in file e2ir.c.
>>
>> Questions:
>>
>> 1. Is this the right place where this lhs-rhs-printing logic should be
>> added? If so could somebody tell me how to make this happen?
>>
>> 2. Is it possible to from within DMD generate expressions that do
>>
>> `import std.stdio : write`
>>
>> and then calls write on the `lhs` and `rsh`...or this a completely
>> wrong approach to solving this problem?
>
> I do think wiring this in the compiler is probably not the right way
> forward. Most language have some library functions like :
>
> expect(exprssion).toBeTrue();
> expect(function/delegate).toThrow!ExceptionType
>
> And so on.
>
> This allow to get nice error and do not need wiring int he language.
> This is extensible and all. I'd rather have something like this.

I encourage making assert smaller seeing (a) it's already used 
everywhere so the benefits will come for free and (b) it's a built-in. 
-- Andrei