Render bug: explicit generic param in call is omitted

[cooldome]

Example :

import macros

proc test(): seq[bool] =
  result = newSeq[bool](2)

macro dumpSym(fn: typed{nkSym}): untyped =
  let fn_impl = fn.getImpl
  echo fn_impl.repr
  echo fn_impl.tree_repr

dumpSym(test)

test proc is rendered in the following way:

proc test(): seq[bool] =
  result = newSeq(2)

The required generic type argument [bool] is omitted from the newSeq call and rendered code does not compile.

[cooldome]

I don't have a clean and simple solution.

Possible solutions:

• Renderer only changes (all most):
  Renderer will detect that called symbol is with sfFromGeneric flag and will render [type list] from
  instantiation info.
  downsides: all generics arguments will be rendered even if they were inferred.
  Possible mitigation: save info which of the generic types were provided by user during symbol
  instantiation and render only them. Still instantiation is done once and reused many types, if user made
  2 calls to one generic proc once providing generic type explicitly and second time it was inferred, both
  these calls will be rendered identically (minor issue in my opinion as long as rendered code compiles).

• Introduce new PNode call kind that will have generic param list stored as one of the arguments of special kind. Rendering becomes super easy, but you can't just add new call kind to nnkCallKinds. This extra special generic argument will cause problems for existing code and it needs to be skipped by codegen and friends.

@Araq:
Let me know what is the preferred solution.

[Araq]

I'm working on a spec for typed ASTs. And this would be a "won't fix, works as by the spec" for me. We must be allowed to reduce call ASTs to only the required information.

[cooldome]

Ok, if we don't want to change AST then renderer only solution from the above should be ok. Renderer will add [args] to every generic sym call.

It will be verbose, but correct. Any issues with this approach?

[Araq]

Well I don't understand how you will accomplish "* Renderer will detect that called symbol is with sfFromGeneric flag and will render [type list] from instantiation info." :-)

[mratsim]

This seems similar to: #7737 (getTypeInst for generics does not gives the full instantiation info in certain cases) and another case of the meta issue with generics + macros (nim-lang/RFCs#44)