By default, the Sprockets DirectiveProcessor introduces a newline between possible 'header' comments and the rest of the JS file. This causes sourcemaps to be offset by 1 line, and therefore breaks browser tooling. We know that Ember-Cli assets do not use Sprockets directives, so we can totally bypass the DirectiveProcessor for those files.
We're using v3 of Sprockets, which is no longer supported - upstreaming a fix will be difficult. Long term, we intend to move away from sprockets.
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