1*3ac0a46fSAndroid Build Coastguard Worker# Build overrides in GN 2*3ac0a46fSAndroid Build Coastguard Worker 3*3ac0a46fSAndroid Build Coastguard WorkerThis directory is used to allow different products to customize settings 4*3ac0a46fSAndroid Build Coastguard Workerfor repos which are DEPS'ed in or shared. 5*3ac0a46fSAndroid Build Coastguard Worker 6*3ac0a46fSAndroid Build Coastguard WorkerFor example: V8 can be built on its own (in a "standalone" configuration), 7*3ac0a46fSAndroid Build Coastguard Workerand it can be built as part of Chromium. V8 defines a top-level 8*3ac0a46fSAndroid Build Coastguard Workertarget, //v8:d8 (a simple executable), which will only be built in the 9*3ac0a46fSAndroid Build Coastguard Workerstandalone configuration. To indiate itis a standalone configuration, v8 can 10*3ac0a46fSAndroid Build Coastguard Workercreate a file, build_overrides/v8.gni, containing a variable, 11*3ac0a46fSAndroid Build Coastguard Worker`build_standalone_d8 = true` and import it (as 12*3ac0a46fSAndroid Build Coastguard Workerimport("//build_overrides/v8.gni") from its top-level BUILD.gn file. 13*3ac0a46fSAndroid Build Coastguard Worker 14*3ac0a46fSAndroid Build Coastguard WorkerChromium, on the other hand, does not need to build d8, and so it would 15*3ac0a46fSAndroid Build Coastguard Workercreate its own build_overrides/v8.gni file, and in it set 16*3ac0a46fSAndroid Build Coastguard Worker`build_standalone_d8 = false`. 17*3ac0a46fSAndroid Build Coastguard Worker 18*3ac0a46fSAndroid Build Coastguard WorkerThe two files should define the same set of variables, but the values may 19*3ac0a46fSAndroid Build Coastguard Workervary as appropriate to suit the needs of the two different builds. 20*3ac0a46fSAndroid Build Coastguard Worker 21*3ac0a46fSAndroid Build Coastguard WorkerThe build.gni file provides a way for projects to override defaults for 22*3ac0a46fSAndroid Build Coastguard Workervariables used in //build itself (which we want to be shareable between 23*3ac0a46fSAndroid Build Coastguard Workerprojects). 24*3ac0a46fSAndroid Build Coastguard Worker 25*3ac0a46fSAndroid Build Coastguard WorkerTODO(crbug.com/588513): Ideally //build_overrides and, in particular, 26*3ac0a46fSAndroid Build Coastguard Worker//build_overrides/build.gni will go away completely in favor of some 27*3ac0a46fSAndroid Build Coastguard Workermechanism that can re-use other required files like //.gn, so that we don't 28*3ac0a46fSAndroid Build Coastguard Workerhave to keep requiring projects to create a bunch of different files to use GN. 29