Passing and modifying arglist across mixins (Sass v3.5.0, Libsass v3.5.0, 3.5.0.beta.3-54-gdebb1e32 bug?)

[bencergazda]

Reduced test case: https://www.sassmeister.com/gist/44340f52a27ad3e4fe61c9772de66d4f

Simplified: I have three mixins:

• a main with a few arguments
• a router, which calls the appropriate main mixin, depending on the situation
• a helper, which calls the original mixin (through the router mixin) with predefined arguments.

It works when I do not use named argument in the helper mixin, but if so, fails on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2, 3.5.0.beta.3-54-gdebb1e32.

Works ok in every cases with other Sass versions: Sass v3.3.14, Sass v3.4.21, Sass 4.0.0.alpha.1

Should I do something otherwise?

input.scss

@mixin main(
  $param1: param1,
  $param2: param2,
  $param3: param3
) {
  param1-value: $param1;
  param2-value: $param2;
  param3-value: $param3;
}

@mixin router($args...) {
  @if (true) { @include main($args...) }
  @else { @include main2($args...) }
}

@mixin helper($args...) {
  @include router($param2: param__2, $args...)
}

.ordinal-arguments {
  /* OK - gets $param2 value from @mixin helper and has the correct $param1 value */
  @include helper(param___1);
}

.named-arguments {
  /* OK on Sass v3.3.14, Sass v3.4.21, Sass 4.0.0.alpha.1,
  but fails on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2,
  (gets $param2 value from @mixin helper, but $param1 has only its default value.)
  
  (Note: It works on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2, when: 
    - in @mixin helper I call "main" instead of "router" (line 17)
    - or if I do not edit the value of $param 2 (line 17) ) */
  @include helper($param1: param___1);
}

Actual results

LibSass v3.5.0.beta.2

/* param1-value should be 'param___1' and param2-value should be param__2 in both cases */
.ordinal-arguments {
  /* OK - gets $param2 value from @mixin helper and has the correct $param1 value */
  param1-value: param___1;
  param2-value: param__2;
  param3-value: param3;
}

.named-arguments {
  /* OK on Sass v3.3.14, Sass v3.4.21, Sass 4.0.0.alpha.1,
  but fails on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2,
  (gets $param2 value from @mixin helper, but $param1 has only its default value.)
  
  (Note: It works on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2, when: 
    - in @mixin helper I call "main" instead of "router" (line 17)
    - or if I do not edit the value of $param 2 (line 17) ) */
  param1-value: param1;
  param2-value: param__2;
  param3-value: param3;
}

Expected result

ruby sass 3.4.21

/* param1-value should be 'param___1' and param2-value should be param__2 in both cases */
.ordinal-arguments {
  /* OK - gets $param2 value from @mixin helper and has the correct $param1 value */
  param1-value: param___1;
  param2-value: param__2;
  param3-value: param3;
}

.named-arguments {
  /* OK on Sass v3.3.14, Sass v3.4.21, Sass 4.0.0.alpha.1,
  but fails on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2,
  (gets $param2 value from @mixin helper, but $param1 has only its default value.)
  
  (Note: It works on Sass v3.5.0.pre.rc.1 and LibSass v3.5.0.beta.2, when: 
    - in @mixin helper I call "main" instead of "router" (line 17)
    - or if I do not edit the value of $param 2 (line 17) ) */
  param1-value: param___1;
  param2-value: param__2;
  param3-value: param3;
}

version info:

var sass = require('node-sass');
console.log(sass.info);

node-sass    4.5.3   (Wrapper)       [JavaScript]
libsass         3.5.0.beta.2    (Sass Compiler) [C/C++]

[bencergazda]

The strange thing is that when nex3 tested locally, got the good results in 3.4.25, 3.5.0-rc.1, 3.5.1, 4.0.0.alpha.1, and bleeding edge 4.0.0. Can I hope that this has been already fixed or should I provide any extra detail?