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upgrading-webkit.md

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Upgrading WebKit

Bun uses a fork of WebKit with a small number of changes.

It's important to periodically update WebKit for many reasons:

  • Security
  • Performance
  • Compatibility
  • …and many more.

To upgrade, first find the commit in bun's WebKit fork (not bun!) between when we last upgraded and now.

cd src/bun.js/WebKit # In the WebKit directory! not bun
git checkout $COMMIT

This is the main command to run:

git pull https://github.com/WebKit/WebKit.git main --no-rebase --allow-unrelated-histories -X theirs

Then, you will likely see some silly merge conflicts. Fix them and then run:

# You might have to run this multiple times.
rm -rf WebKitBuild

# Go to Bun's directory! Not WebKit.
cd ../../../../
make jsc-build-mac-compile

Make sure that JSC's CLI is able to load successfully. This verifies that the build is working.

You know this worked when it printed help options. If it complains about symbols, crashes, or anything else that looks wrong, something is wrong.

src/bun.js/WebKit/WebKitBuild/Release/bin/jsc --help

Then, clear out our bindings and regenerate the C++<>Zig headers:

make clean-bindings jsc-bindings-headers generate-builtins

Now update Bun's bindings wherever there are compiler errors:

# It will take awhile if you don't pass -j here
make jsc-bindings-mac -j10

This is the hard part. It might involve digging through WebKit's commit history to figure out what changed and why. Fortunately, WebKit contributors write great commit messages.