{"action":"opened","issue":{"url":"https://api.github.com/repos/ember-cli/ember-cli/issues/4647","labels_url":"https://api.github.com/repos/ember-cli/ember-cli/issues/4647/labels{/name}","comments_url":"https://api.github.com/repos/ember-cli/ember-cli/issues/4647/comments","events_url":"https://api.github.com/repos/ember-cli/ember-cli/issues/4647/events","html_url":"https://github.com/ember-cli/ember-cli/issues/4647","id":100152853,"number":4647,"title":"less/sass/stylus rebuilds are slow","user":{"login":"stefanpenner","id":1377,"avatar_url":"https://avatars.githubusercontent.com/u/1377?v=3","gravatar_id":"","url":"https://api.github.com/users/stefanpenner","html_url":"https://github.com/stefanpenner","followers_url":"https://api.github.com/users/stefanpenner/followers","following_url":"https://api.github.com/users/stefanpenner/following{/other_user}","gists_url":"https://api.github.com/users/stefanpenner/gists{/gist_id}","starred_url":"https://api.github.com/users/stefanpenner/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/stefanpenner/subscriptions","organizations_url":"https://api.github.com/users/stefanpenner/orgs","repos_url":"https://api.github.com/users/stefanpenner/repos","events_url":"https://api.github.com/users/stefanpenner/events{/privacy}","received_events_url":"https://api.github.com/users/stefanpenner/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2015-08-10T19:49:00Z","updated_at":"2015-08-10T19:49:00Z","closed_at":null,"body":"Although not ember-cli issue directly, this obviously affects everyone. (including myself)\r\n\r\nnote: the fact that less/sass/stylus rebuild at all, is partially do to https://github.com/ember-cli/ember-cli/issues/4646\r\n\r\nThat being said, if no css changed, one would expect the rebuild to be a noop. The reality is, today all the css pre-process try to be magical. Allowing virtually anything possible to be imported, this though means it must diff anything possible, to decide if it should rebuild or not. Turns out, diffing [everything is slow](https://github.com/ember-cli/ember-cli/issues/4460) and as the fix to #4460 demonstrates, reducing the scope of what is diff, obviously results in an improved experience.\r\n\r\nI believe the short term solution, is to update the various css preprocessor tools, to require the developer explicitly provide loadPaths (that should be diffed). Future iterations can explore better integration with the underlying css pre-processsors, but by pushing this slight effort to the developers. We can get some dramatic performance wins in the short term."}}