Throwing custom errors/warnings in Sass - sass

Question

I'm creating a font module which contains all my webfonts and some Sass mixins to write out the #font-face declarations. The main mixin will be something like includeFont(name, weight, style).
I'll keep a record in some Sass variable(s) of which fonts at which weights and styles are actually available, and through being clever about this I think I can write the mixin so that I can detect if I try and request a font that doesn't exist.
But when I detect that situation, how can I throw an error?

Answer 1

As of Sass 3.4.0, there's an #error directive you can use to cause a fatal error:
$stuff: fubar;
#if ($stuff == fubar) {
#error "stuff is fubar";
}
If you try to compile this at the shell, you'll see the following:
$ sass test.scss
Error: stuff is fubar
on line 3 of test.scss
Use --trace for backtrace.
There are also related #warn and #debug directives which have been in the language for longer, in case those are more useful to you. Example:
#debug "stuff is happening";
#warn "stuff is happening that probably shouldn't be happening";
/*
Note that these directives do not terminate execution, and this block
will therefore still be output.
*/
* {
color: pink;
}
When compiled:
$ sass test2.scss
test2.scss:1 DEBUG: stuff is happening
WARNING: stuff is happening that probably shouldn't be happening
on line 2 of test2.scss
/*
Note that these directives do not terminate execution, and this block
will therefore still be output.
*/
* {
color: pink; }