LESS compilation on Play 2 is seriously slow

Question

LESS compilation in my fresh Play 2 install is genuinely slow. Even after placing an '_' on files that do not need direct compilation, a page refresh after a LESS edit takes ~8 seconds to complete. This is compared to a local compile using Codekit which takes less than a second.

Any suggestions on speeding up this process? Is it worth filing a bug against Play to have this looked at?

Here are details on my file sizes: My LESS setup is very simple. _reset.less (.5k) _desktop.less (13k), _tablet.less (10k), _mobile.less (8k), _sprites.less (25k) files. An all.less (.3k) file that puts it all together. That's it. The resulting css file is 53k.

Bedeck

how many less files do you have? How big each? – Stroke

My LESS setup is very simple. _reset.less (.5k) _desktop.less (13k), _tablet.less (10k), _mobile.less (8k), _sprites.less (25k) files. An all.less (.3k) file that puts it all together. That's it. The resulting css file is 53k. – Bedeck

I think there might be a way to tell Play to use the native less app instead of the interpreted one via Rhino. But I can't find any docs on that. :( – Nun

I've noticed this problem, too. It's bad enough that I'm considering switching to the play-sass plugin, which uses the Sass Ruby gem and the sass command. Either that, or I'm considering writing my own plugin that uses lessc (assuming I can't figure out how to do that via whatever configuration parameter James Ward mentioned... time to crawl the source, I suppose). In any case, there's an experimental setting that may help you. See the bottom of playframework.org/documentation/2.0.1/Assets, where it talks about the incrementalAssetsCompilation setting. – Vaulted

Answer 1

I did a write-up of a small investigation into this problem. You can find it here.

Bottom line: I get faster performance by switching to Sass. It's not hard to do. Use the Play-Sass SBT plugin and, if you're using Bootstrap, use the SASS Bootstrap files from the sass-twitter-bootstrap project.

Precompiling your LESS files via the lessc command is another solution, and it's quite fast.

Assuming your project uses Bootstrap, using a precompiled Bootstrap, rather than the Bootstrap LESS files, is also a big win, because the Play LESS compiler recompiles all LESS files when one of them changes, and Bootstrap is rather large. But, for some of us, using a precompiled Bootstrap is inconvenient...

Using Play 2.0's Rhino-based, on-demand LESS compilation is the slowest option. Pig-slow, in fact. And ignore my comment about incrementalAssetsCompilation. It's documented, but it does not appear to be in the 2.0.x code base.

EDIT (22 May, 2013) Jonathan Parsons has put together a play-lessc plugin that uses the lessc command to compile LESS files. It can dramatically decrease LESS compilation times in a Play project. See https://github.com/jmparsons/play-lessc

Vaulted

Answer 2

This will dramatically reduce the compilation time:

export SBT_OPTS="$SBT_OPTS -Dsbt.jse.engineType=Node"

It makes Play use Node instead of Rhino when running JavaScript.

Viniculture

Answer 3

From Play Framework 2.3, you can use node.js as default JavaScript engine, which is used for less compilation, js lint, CoffeeScript etc..

Download and install node.js (https://nodejs.org) library and put

JsEngineKeys.engineType := JsEngineKeys.EngineType.Node

to build.sbt.

Reference #1 - Reference #2

Subterrane