assets: enable less source maps

[jmartinm]

Following up on #2921 I have come to the conclusion that our extension code could be simplified by dropping support for LESS_RUN_IN_DEBUG.

This would avoid, for instance, the following 'hack' that needed to be introduced https://github.com/inveniosoftware/invenio/pull/2922/files#diff-dc717d85d0b109c334416b4b5a305f8cR136

What this variable does is enabling compilation of less files in the browser http://lesscss.org/#client-side-usage

But this does not offer any advantage as far as I can see.

By default webassets will do the right thing and if a less file on a Bundle is modified, upon page refresh, the bundle is recompiled and changes are visible immediately. If there are no changes then no compilation happens.

This is a WIP branch where I show what the change would be jmartinm@5fdd9c0

Proposal

• Drop support for LESS_RUN_IN_DEBUG (See this commit) (PR assets: removal of LESS_RUN_IN_DEBUG support #3001)
• Enable less source maps (http://robdodson.me/debug-less-with-chrome-developer-tools/) - no less.js needed
• Fix depends= parameter used, for example, here so that we can have imports in the less code like here and a change on any of the dependent files will trigger recompilation of less. This is currently not happening, likely due to something missing in our custom resolver

I think this would make working with less nice while simplifying our code.

What do you think? Anybody using less.js in the browser? Or there is a good reason for keeping it that I am missing?

[jacquerie]

+1 on all three points (is that a +3?). Even the author of less.js agrees on client side compilation: less/less.js#1541 (comment).

[lnielsen]

Personally I never used LESS_RUN_IN_DEBUG=True so I'm fine with the change if it implies the code.

[jirikuncar]

@drjova @egabancho can we proceed with removing support for LESS_RUN_IN_DEBUG in 2.1?

[drjova]

👍

[tiborsimko]

For better tracking, we should probably close this RFC now as agreed upon, and open a new task to implement the removal with a concrete future milestone.

[jirikuncar]

@jmartinm you can proceed with removing the support for LESS_RUN_IN_DEBUG.

[jmartinm]

Sure, so shall I close this RFC and create 3 issues with the 3 bullet points proposed at the beginning?

[jirikuncar]

@jmartinm we can keep this issue open and you just address this issue in new commits.

[jmartinm]

👍

[joelharkes]

You're doing great work guys! any idea when we can expect this feature to be released?

[lnielsen]

@joelharkes This has been superseded by https://github.com/inveniosoftware/invenio-theme which now uses Sass instead of Less.