A Vision on Improved DMD Template Instantiation Diagonostics

[via Digitalmars-d]

After having seen Andrei's & Walter's talks on DConf 2015 it's 
time reveal a dream of mine. It resolves around of feature that I 
believe is one of the most important improvements that will 
benefit aggregation of more *new* users to the D Community.

Namely a more clever DMD diagnostics when a template instantion 
fails to match any template definition in the current scope.

For instance, if

     f(a,b,c,d)

fails to match any of the overloads

     f(a,b,c) if (PRED_1(a,b,c) && PRED_2(a,b,c))
     f(a,b,c,d) if (PRED(a,b) && PRED(b,c) && PRED(c,d))

instead of saying

     > Error: neither of these matched
     > - f(a,b,c) if (PRED_1(a,b,c) && PRED_2(a,b,c))
     > - f(a,b,c,d) if (PRED(a,b) && PRED(b,c) && PRED(c,d))

it should instead say

     > Error: no template match to call of
     > f(a,b,c,d)
     > for neither

     > - f(a,b,c) if (PRED_1(a,b,c) && PRED_2(a,b,c))
                                       -------------
     >   because template restriction `PRED_2(a,b,c)` evaluate to 
false

     > - f(a,b,c,d) if (PRED(a,b) && PRED(b,c) && PRED(c,d))
                                     ---------
     >   because template restriction `PRED(b,c)` evaluated to 
false

Eventhough this might be a bit tricky to get right and may break 
lots of existing diagnostics (in DMD unittests), I'd say it's 
definitiely worth effort. Such a feature would attract lots of 
new users not used to D's advanced template restrictions. All 
users, newbies aswell as experts, would be benefit from this 
feature. I you DMD review guys are interested in getting this in 
and helping me out on source code directions I'd be very happy to 
start working on DMD PR for this.

Destroy.