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+# What is GN? |
+ |
+GN is a meta-build system that generates [NinjaBuild](NinjaBuild.md) |
+files. It's meant to be faster and simpler than GYP. It outputs only |
+Ninja build files. |
+ |
+## Why bother with GN? |
+ |
+1. We believe GN files are more readable and more maintainable |
+ than GYP files. |
+2. GN is fast: |
+ * GN is 20x faster than GYP (as of mid November, building 80% |
+ of what GYP builds, in one configuration rather than two, takes 500ms |
+ on a z620 running Ubuntu Trusty. GYP takes 20 seconds. |
+ We see similar speedups on Mac and Windows). |
+ * GN supports automatically re-running itself as needed by Ninja |
+ as part of the build. This eliminates the need to remember to |
+ re-run GN when you change a build file. |
+3. GN gives us better tools for enforcing dependencies (see |
+ `gn check` and the `visibility`, `public_deps`, and `data_deps` |
+ options for some examples). |
+4. GN gives us tools for querying the build graph; you can ask |
+ "what does X depend on" and "who depends on Y", for example. |
+ |
+## What's the status? |
+ |
+_as of 8 Feb 2015:_ |
+ |
+Chrome and most of the major test suites link on Linux and ChromeOS. |
+There's probably <1000 objects left to build, in a few test suites and a |
+bunch of utillities and helper binaries. We will probably have |
+everything converted in another couple weeks. |
+ |
+Chrome also links on Android and Windows, and bringing up the remaining |
+test suites should be mostly straightforward. There's some work left to |
+enable NaCl on Windows but it should also be straightforward. |
+ |
+Mac and iOS have not progressed much as attention has been focused on |
+Linux and Windows; we still need support for bundles and frameworks |
+before it can get to parity w/ the other platforms. |
+ |
+## When are you going to be done? |
+ |
+_as of 8 Feb 2015:_ |
+ |
+We're currently shooting for having the main developer configurations |
+working and usable by the end of March 2015. There will probably be a |
+fair amount of verification of flags, bug fixes, etc over the next |
+couple months, but hopefully we will be flipping configurations from GYP |
+to GN throughout Q2, targeting having everything done by the end of Q2. |
+ |
+## What does "done" mean? |
+ |
+Ideally we're done when all of the GYP files have been deleted from |
+Chromium and no one misses them. |
+ |
+We will be "mostly" done when the following are true: |
+ * All of the bots maintained by the Chrome infra team for Chromium and |
+ downstream of Chromium have been switched to GN. (Upstream projects |
+ like Skia and V8 can choose to stay on GYP if they like). |
+ * Any developer configurations we care about that don't have bots also |
+ work (Generally speaking, we're aiming to not have any of these. |
+ * Configurations we care about should have bots to ensure they don't |
+ break). We have verified that all of the tests pass. We have |
+ verified that the command lines match in the above configurations as |
+ much as possible, and we accept any differences. We have reviewed |
+ any binary differences that result in the official builds and |
+ accepted them. The GN files are the "source of truth" for the |
+ build, and normal chromium developers normally do not need to touch |
+ GYP files to keep things working. We have replacements for the |
+ hybrid "msvs-ninja" and "xcode-ninja" configurations that GYP can |
+ currently build. |
+ |
+The difference between "mostly done" and "done" exists to cover any |
+issues we haven't yet identified :) |
+ |
+We do not currently plan to support full native XCode or Visual Studio |
+generation from GN. It is theoretically possible to support such things, |
+so we would at least look at patches adding the functionality. |
+ |
+## How can I help? |
+ |
+Check to see if your targets build under GN yet. If they don't, |
+volunteer to help convert them! |
+ |
+_17 Nov 2014. We are updating the stuff we use to track progress. Watch |
+this space and chromium-dev@ for more info!_. |
+ |
+## I want more info on GN! |
+ |
+Read these links: |
+ |
+ * [Quick start](docs/quick_start.md) |
+ * [FAQ](docs/faq.md) |
+ * [GYP conversion cookbook](docs/cookbook.md) |
+ * [Language and operation details](docs/language.md) |
+ * [Style guide](docs/style_guide.md) |
+ * [Cross compiling and toolchains](docs/cross_compiles.md) |
+ * [Hacking on GN itself](docs/hacking.md) |
+ * [GNStandalone](docs/standalone.md) Standalone GN projects |
+ * [UpdateGNBinaries](docs/update_binaries.md) Pushing new binaries |