nim 1.6.0 savePNG results in too nested template instantiation

[ftsf]

Nim Compiler Version 1.6.0 [Windows: amd64]

  savePNG(filename, data, LCT_RGBA, 32, swCanvas32.w, swCanvas32.h)

results in:

C:\Users\user\git\nico\nico\backends\sdl2.nim(807, 10) template/generic instantiation of `savePNG` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(3131, 18) template/generic instantiation of `savePNGImpl` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(3002, 26) template/generic instantiation of `encodePNG` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(2967, 21) template/generic instantiation of `encodePNG` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(2954, 17) template/generic instantiation of `encoderCore` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(2873, 18) template/generic instantiation of `frameConvert` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(2833, 24) template/generic instantiation of `preProcessScanLines` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(2642, 13) template/generic instantiation of `filter` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG.nim(2620, 30) template/generic instantiation of `filterMinsum` from here
C:\Users\user\.nimble\pkgs\nimPNG-#head\nimPNG\filters.nim(138, 31) Error: template instantiation too nested

[jangko]

please report this to Nim repo as a regression. it is very hard to fix it from nimPNG.

[ftsf]

Hmm, I've just gone and tested this with Nim 1.4 and Nim 1.2 and get the same behaviour, so it seems this is not caused by a recent change in Nim.

[ftsf]

Testing using a cutdown example doesn't reproduce the problem.

import nimPNG
import os
import strformat
import strutils
import times
import sdl2_nim/sdl

var swCanvas32: Surface
var writePath = "."

proc saveScreenshot*() =
  echo "saveScreenshot"
  createDir(writePath & "/screenshots")
  let filename = joinPath(writePath, joinPath("screenshots", "screenshot-$1T$2.png".format(getDateStr(), getClockStr())))
  var data = newSeq[uint8](swCanvas32.w * swCanvas32.h * 4)
  copyMem(data[0].addr, swCanvas32.pixels, swCanvas32.w * swCanvas32.h * 4)
  var res = savePNG(filename, data, LCT_RGBA, 32, swCanvas32.w, swCanvas32.h)
  echo "saved screenshot to: ", filename

saveScreenshot()

Compiles successfully, but similar code used in nico gives the original error, though I'm unsure why, will investigate further.

[jangko]

looks like a global scope pollution to me. some inner template in filters.nim might collide with other template from somewhere.
a workaround is, you can write a helper module+proc to force instantiate nimPNG generics and then reexport those non-generic proc.