C codegen issue with fieldPairs and Karax DSL

[ajusa]

This snippet below fails to compile with gcc. I realize that this is probably adding quite a bit of complexity with the Karax DSL, but I'm not super sure how to minimize further. I was able to get it to fail in the playground as well, on 1.6 and 1.4.8

Example

import karax/[vdom, karaxdsl]
proc generateInputs[T](obj: T): VNode =
  buildHtml(tdiv):
    for name, placeholder in obj.fieldPairs:
      label:
        text name
        input(type="text", name=name, placeholder=placeholder)
type RegisterForm = object
  name: string
  email: string

echo $generateInputs(RegisterForm(name: "ajusa", email: "something@gmail.com"))

Current Output

Exists on devel as well

Hint: used config file '/home/ajusa/.choosenim/toolchains/nim-1.6.0/config/nim.cfg' [Conf]
Hint: used config file '/home/ajusa/.choosenim/toolchains/nim-1.6.0/config/config.nims' [Conf]
..................................................................................
CC: stdlib_digitsutils.nim
CC: stdlib_assertions.nim
CC: stdlib_dollars.nim
CC: stdlib_io.nim
CC: stdlib_system.nim
CC: stdlib_math.nim
CC: stdlib_strutils.nim
CC: ../../.nimble/pkgs/karax-1.2.1/karax/vstyles.nim
CC: ../../.nimble/pkgs/karax-1.2.1/karax/vdom.nim
CC: ../../.nimble/pkgs/karax-1.2.1/karax/compact.nim
CC: testing.nim
/home/ajusa/.cache/nim/testing_d/@mtesting.nim.c: In function ‘generateInputs_testing_12’:
/home/ajusa/.cache/nim/testing_d/@mtesting.nim.c:192:66: error: redeclaration of ‘tmp_2’ with no linkage
  192 |         tyObject_VNodecolonObjectType___UzLz41HuYz7DVA9bD3pvmag* tmp_2;
      |                                                                  ^~~~~
/home/ajusa/.cache/nim/testing_d/@mtesting.nim.c:187:66: note: previous declaration of ‘tmp_2’ with type ‘tyObject_VNodecolonObjectType___UzLz41HuYz7DVA9bD3pvmag *’
  187 |         tyObject_VNodecolonObjectType___UzLz41HuYz7DVA9bD3pvmag* tmp_2;
      |                                                                  ^~~~~
/home/ajusa/.cache/nim/testing_d/@mtesting.nim.c:195:66: error: redeclaration of ‘tmp_3’ with no linkage
  195 |         tyObject_VNodecolonObjectType___UzLz41HuYz7DVA9bD3pvmag* tmp_3;
      |                                                                  ^~~~~
/home/ajusa/.cache/nim/testing_d/@mtesting.nim.c:190:66: note: previous declaration of ‘tmp_3’ with type ‘tyObject_VNodecolonObjectType___UzLz41HuYz7DVA9bD3pvmag *’
  190 |         tyObject_VNodecolonObjectType___UzLz41HuYz7DVA9bD3pvmag* tmp_3;
      |                                                                  ^~~~~
Error: execution of an external compiler program 'gcc -c  -w -fmax-errors=3   -I/home/ajusa/.choosenim/toolchains/nim-1.6.0/lib -I/home/ajusa/Documents/example -o /home/ajusa/.cache/nim/testing_d/@mtesting.nim.c.o /home/ajusa/.cache/nim/testing_d/@mtesting.nim.c' failed with exit code: 1

Expected Output

Not sure, but it should be some HTML code. At the very least I should get a Nim compiler error or correct output.

$ nim -v
Nim Compiler Version 1.6.0 [Linux: amd64]
Compiled at 2021-10-19
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 727c6378d2464090564dbcd9bc8b9ac648467e38
active boot switches: -d:release

Might be related to #15637, it has a similar error message but the code is very different. Interestingly, if I make the type only have one field (such as name, without email) then it compiles and runs just fine.