Play well with Custom Syntax

[RyanZim]

This is still a WIP. Will most likely need rebased when I'm done.

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Warning: This is a weird approach to solving this problem.

Perhaps this approach is naive; but it should be pretty well bulletproof. It is based on the (correct 😛 ) assumption that if a parser can parse the input, it is the correct parser.

If the file is .sss, it tries that parser first. For all other files (or if SugarSS parsing fails) it tries the user-passed parser (if available). If that fails, it tries the default parser.

The reason I chose this approach is that we have no reliable way of telling if result.opts.parser is a CSS-compliant parser. See #242 for more background.

The main problem with this approach is error handling/reporting. Currently, it gives the user the error from the default parser. In the case of a malformed .sss import, this is quite unhelpful. Not sure what is the best route to improve this.

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This is by no means a polished PR. I may end up totally rewriting the implementation. Anyway, it does provide a good test suite for how things should behave.

CC: @ai @MoOx

[ai]

Awesome! You did big work in short time :).

[RyanZim]

@ai @MoOx Made a change so that only the SugarSS parser is tried when the extension is .sss. That should fix some of the incorrect errors.

You're still stuck with bad errors if you're using a css-compliant parser and make a syntax error. You will get the error message from the default parser. 😢 Thoughts?

[ai]

Looks like good. But sorry, I have no postcss-import case to test it.

[MoOx]

I can't help, I never used anything that raw css.

[RyanZim]

I don't use custom parsers either.

Do you think this error problem is big enough to block this PR? We can always change error reporting later.

[RyanZim]

@ai @MoOx Not sure if it's worth adding support for .scss file extensions or not. What do you think?

[ai]

Sure, complicated question. I afraid that user will try to import real SCSS sources (not just with // comments).

Let's start without it, and add it later if user will ask for it (at least we have use cases from them).

[RyanZim]

@ai That's what I was thinking.

I'll rebase this and then leave it for final review before merging it.

[RyanZim]

@ai @MoOx Anything else that needs changed? If not, I will merge this.

[ai]

LGTM

[RyanZim]

OK, merging.