Incorrectly allowing functions to be defined in control directives or mixins

[xzyfer]

Originally reported on Twitter - https://twitter.com/kaelig/status/643584415789154304

Functions may not be defined within control directives or mixins but LibSass allows it i.e.

@if (true) {
  @function foo() {
    @return 'foo';
  }
}

Should produce the following error but does not

Error: Functions may not be defined within control directives or other mixins.

[xzyfer]

Other notable cases where we should, but don't throw this error.

@mixin foo() {
  @function foo() {
    @return 'foo';
  }
}

$i: 1;
@while $i == 1 {
  @function foo() {
    @return 'foo';
  }
  $i: $i + 1;
}

@each $i in (1) {
  @function foo() {
    @return 'foo';
  }
}

@for $i from 1 through 2 {
  @function foo() {
    @return 'foo';
  }
}

[saper]

Nice enhancement :) Closures, anyone?

[xzyfer]

I like it, but it's not Sass :(

[xzyfer]

Turns out this also affects mixins

@mixin foo() {
  @mixin bar() {
    @return 'foo';
  }
}

[saper]

Let's open an enhancement proposal :)

[xzyfer]

https://twitter.com/chriseppstein/status/643584546298986496

[perplexes]

Just ran into this with Igosuki/compass-mixins#34 / Igosuki/compass-mixins#67. It's trying to define compact if it doesn't exist. Since compact was stripped from libsass, this is needed to put it back in, in a version independent way.

Currently (as of b2a3d98) function definition is scoped to the control block, breaking this usage (@if not(function-exists(compact)) { ....). Causing this funny behavior: https://gist.github.com/perplexes/e0e75f00b3772f2bf643. It seems to not register with the globals, so even function-exists breaks within the block.

Current work-around is to just remove the if statement (since in my codebase I know we need it). Any suggestions on what compass-mixins can do, though? Maybe a function-if-not-exists directive?