ch-ch-changes

[Nick Sabalausky]

"Daniel Keep" <daniel.keep.lists at gmail.com> wrote in message 
news:glrlgi$2bu4$1 at digitalmars.com...
>
>
> Nick Sabalausky wrote:
>> "Daniel Keep" <daniel.keep.lists at gmail.com> wrote in message
>> news:glqu65$15pi$1 at digitalmars.com...
>>>
>>> Christopher Wright wrote:
>>>> Don wrote:
>>>>> [snip]
>>>>>
>>>>> Then we get:
>>>>> static assert(__traits(mixincompiles, comp), "Predicate: " ~ comp ~ "
>>>>> does not compile");
>>>>>
>>>>> mxin(comp);
>>>> That's certainly prettier.
>>> Still doesn't give the user a reason for WHY their predicate didn't
>>> compile...
>>>
>>> It's a pity we can't do this (or something similar):
>>>
>>> template Something(string comp)
>>> {
>>>    static assert( __traits(mixincompiles, comp),
>>>        "Predicate q{"~comp~"} does not compile, because:\n"
>>>        ~__traits(mixinerrors, comp,
>>>                  Something.instantiationFile,
>>>                  Something.instantiationLine) );
>>> }
>>>
>>>  -- Daniel
>>
>> I'd much rather see errors and static asserts inside of a template cause 
>> the
>> compiler to automatically output a template instantiation "stack trace" 
>> (for
>> lack of a better term). Ie, list files/lines starting with the deepest
>> file/line, and then the file/line that instantiated that template, and if
>> that was also inside a template, then the file/line that instantiated 
>> that,
>> etc.
>
> I'd certainly like to see better error reporting for template errors,
> but I think the ultimate goal should be to be able to write template
> that, when they do something wrong, can tell the user SPECIFICALLY what
> they did wrong.
>

I would think those two things would compliment each other nicely. To modify 
your examples:

template Something(string comp)
{
   static assert( __traits(mixincompiles, comp),
       "Predicate q{"~comp~"} does not compile, because:\n"
       ~__traits(mixinerrors, comp) );
}

Result:
Predicate blah does not compile, because: blah
file/line of static assert
file/line where Something was actually instantiated

My main original point is just that the writer of the meaningful diagnostic 
message shouldn't have to manually deal with the file/line that attempted 
the failed instatiation. It should just simply get shown by the compiler 
saying "Error or static asset failure inside a template? I'd better spit out 
*both* relevant files/lines along with the error/assert message". The 
programmer shouldn't have to do that manually.