Accessing global Sass variables from within Sass functions written in JS

[JohnAlbin]

Copying this issue from the node-sass queue, sass/node-sass#1297.

Using the new experimental functions feature of libSass, I can write a Sass function in JavaScript. But I'm running into problems trying to access global Sass variables.

It is common for Sass module developers to specify the default values of their mixin or function parameters as equaling a global variables value. e.g.

@function hi($name: $my_module_global) {
  @return "Hello, #{$name}";
}

But I get an error when I try to specify a global variable in the function definition in JS-land. Specifically, doing this:

var sass = require('node-sass');

sass.render({
  data: '$my_module_global: "World"; .test { content: hi(); }',
  functions: {
    'hi($name: $my_module_global)': function(name, done) {
      done(sass.types.String('Hello, ' + name.getValue() + '!'));
    }
  }
}, function(error, result) {
  console.log(result ? result.css.toString() : error);
});

gives me this error:

Error: Undefined variable: "$my-module-global".
        on line 1 of [c function]
>> hi($name: $my_module_global)
   ----------^

Now, if you say its not possible to use a global variable in the string that contains the function and parameters names ('hi($name: $my_module_global)'), I'm cool with that.

However, I would still need to access Sass global variables from within the main body of my function. Like this:

var sass = require('node-sass');

sass.render({
  data: '$my_module_global: "World"; .test { content: hi(); }',
  functions: {
    'hi($name: "nocanhazglobalhere")': function(name, done) {
      // How do I access global Sass variables like $my_module_global in here?
      done(sass.types.String('Hello, ' + name.getValue() + '!'));
    }
  }
}, function(error, result) {
  console.log(result ? result.css.toString() : error);
});

I'm not sure if this is a missing part of the API in libSass. I looked at https://github.com/sass/libsass/blob/master/docs/api-function.md but there are parts of it I don't understand.

[mgreter]

This was implemented with #2251