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Running Against ToT WebKit in the Simulator

This is a simplified workflow intended to make it as easy as possible to compile and run against ToT WebKit locally. If you intend to do daily development in a WebKit tree, you may want to consider an alternate workflow as described here.

A design doc explaining the details behind these steps can be found here

Note: this only works on Simulator. At present, we do not have the ability to compile WebKit for devices.

Warning: do this in a new checkout

The changes below will substantially increase compile times, for both clean and incremental builds. No-op builds will jump from ~0s to ~60s, which will likely be an unacceptable regression in a daily development checkout.

By pulling a separate, new checkout for WebKit, you sidestep these issues at the expense of greater disk usage.

Updating .gclient to pull WebKit

To start, edit your .gclient file to checkout WebKit @HEAD. Both of the custom variables are necessary, as by default webkit.git is pinned to a revision in the distant past.

solutions = [
  {
    "url": "https://chromium.googlesource.com/chromium/src.git",
    "name": "src",

    "custom_vars": {
      "checkout_ios_webkit": True,
      "ios_webkit_revision": "refs/heads/master",
    },

  },
]
target_os = ["ios"]
target_os_only = "True"

Add the custom_vars section as above and re-run gclient sync. After it completes, you should have a WebKit checkout in ios/third_party/webkit/src.

Building

WebKit-enabled checkouts expose a webkit target via GN/ninja. The WebKit libraries will automatically be built as part of the default set of targets, or you can build it individually.

# Builds all targets, including webkit.
ninja -C out/Debug-iphonesimulator

# Builds just the webkit target.
ninja -C out/Debug-iphonesimulator webkit

The WebKit build output can be found at out/Debug-iphonesimulator/obj/ios/third_party/webkit/.

Speeding up clean builds by building WebKit first

We build using a set of scripts provided by WebKit; they set up an environment and then invoke xcodebuild directly. To prevent xcodebuild from competing with ninja for CPU/RAM, we limit the WebKit build to four parallel jobs. This is generally sufficient for incremental builds, but for clean builds (or after a sync) it may be faster to build WebKit without this limitation.

# After a sync, build WebKit first.
ios/third_party/webkit/build-webkit.py

# Once WebKit is built, invoke ninja as usual to build Chromium.
ninja -C out/Debug-iphonesimulator

One-time setup (per machine, per version of Xcode)

If you move to a new machine or install a new version of Xcode, you'll need to run a setup script in order to copy some headers from the macOS SDK into the iOS SDK.

sudo ios/third_party/webkit/src/Tools/Scripts/configure-xcode-for-ios-development

Running against locally-built libraries

To run against the libraries you've just built, set the DYLD_FRAMEWORK_PATH environment variable to the directory containing the WebKit build output. This is usually easiest to do in the Xcode UI.

DYLD_FRAMEWORK_PATH = /path/to/out/Debug-iphonesimulator/obj/ios/third_party/webkit/Debug-iphonesimulator/