sbt plugin with a workflow for big projects

License: Apache-2.0

Language: Scala

Windows GNU / Linux
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The workflow introduced by this plugin gives huge time saving benefits to developers in extremely large projects (hundreds of Projects), where you may often make non-ABI changes in a middle layer and then run your application or tests in the top layer.

Various forms of caching are used to reduce the lag-time and overhead of basic tasks such as compile or test.


The biggest workflow change that sbt-big-project introduces is that it forces all projects to compile to jar, instead of just class directories, and sbt will treat each project independently. If a jar exists for a Project, sbt will treat it as a library dependency and will not perform incremental compilation on that project unless explicitly requested.

If your site makes snapshot jars available from CI jobs, you can customise your sbt build to download and copy those jars into their expected place, entirely avoiding the need to compile many projects on your desktop.

Let us consider a trivial example, consisting of three Projects: a, b and c, with c depending on b which depends on a. If you make source code changes within a, and type a/compile then the next time you run your app or tests in c, then b will not be recompiled.


If you knowingly make breaking ABI changes to a, you should tell sbt by typing a/breakingChange which will flag all dependents of a as requiring a full recompile.


There is a convenient global task, breakOnChanges, which will scan for changes to your source and resource files and automatically declare all the changes to be breaking.

This can be adopted as part of your workflow if you cherry pick or merge a colleague's work and wish to minimise the number of Projects that you recompile, whilst remaining completely safe from ABI changes that your colleagues may have introduced. (Of course, if the rebase changes core libraries, you will still incur a full recompile).


This plugin uses a source-only distribution mechanism to make it easy to install in corporate environments.

You must be using sbt version 0.13.11 or later.

You must also be using class-monkey, so download it and add to your SBT_OPTS.

To install, copy the BigProjectSettings.scala from the latest tagged release into your project directory and then edit your Projects to have the BigProjectKeys.overrideProjectSettings applied for each of your configurations that the Project supports. e.g.

val a = project settings (BigProjectSettings.overrideProjectSettings(Compile, Test))
val b = project dependsOn(a) settings (BigProjectSettings.overrideProjectSettings(Compile, Test, IntegrationTests))
val c = project dependsOn(b) settings (BigProjectSettings.overrideProjectSettings(Compile, Test))

val root = Project("root", file(".")) aggregate (a, b, c) settings (
  BigProjectSettings.overrideProjectSettings(Compile, Test)

This plugin is unforgiving of bad builds (e.g. an incorrect aggregating rootProject). If you need help fixing your build before using this plugin, ask in or Stack Overflow.

Some customisations are made available in the BigProjectKeys object, such as support for Eclipse-style test projects. As the site installer of sbt-big-project, you are expected to read the documentation in the source code, and to familiarise yourself with the accompanying tests in the src/sbt-test folder.

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Sam Halliday Vladimir Polushin

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v1.1.0 November 26, 2016
v1.0.0 February 06, 2016

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sbt plugin with a workflow for big projects
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