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Updating Clang format binaries

Instructions on how to update the clang-format binaries that come with a checkout of Chromium.

Prerequisites

You'll also need permissions to upload to the appropriate google storage bucket. Chromium infrastructure team members have this, and others can be granted the permission based on need. If you need this permission, mention this in the tracking bug.

Fetch and upload prebuilt clang-format binaries from recent clang rolls

Recent clang rolls can be found via looking at the history of update.py. You can also use clang-format packages built in recent successful dry run attempts at updating clang as mentioned here.

The following will, for each supported host architecture,

  • Fetch the corresponding clang-format package from the specified clang roll
  • Extract and copy the clang-format binary to the proper directory
  • Upload the binary into a publicly accessible google storage bucket, also updating the corresponding .sha1 files in the local checkout of Chrome
cd $SRC/chromium/src

GS_PATH=gs://chromium-browser-clang-staging
CLANG_REV=llvmorg-15-init-234-g567890abc-2

echo Linux
gsutil cp $GS_PATH/Linux_x64/clang-format-$CLANG_REV.tgz /tmp
tar xf /tmp/clang-format-$CLANG_REV.tgz -C buildtools/linux64 --strip-component=1 bin/clang-format

echo Win
gsutil cp $GS_PATH/Win/clang-format-$CLANG_REV.tgz /tmp
tar xf /tmp/clang-format-$CLANG_REV.tgz -C buildtools/win --strip-component=1 bin/clang-format.exe

echo 'Mac x64'
gsutil cp $GS_PATH/Mac/clang-format-$CLANG_REV.tgz /tmp
tar xf /tmp/clang-format-$CLANG_REV.tgz -C buildtools/mac --strip-component=1 bin/clang-format
mv buildtools/mac/clang-format buildtools/mac/clang-format.x64

echo 'Mac arm64'
gsutil cp $GS_PATH/Mac_arm64/clang-format-$CLANG_REV.tgz /tmp
tar xf /tmp/clang-format-$CLANG_REV.tgz -C buildtools/mac --strip-component=1 bin/clang-format
mv buildtools/mac/clang-format buildtools/mac/clang-format.arm64

echo 'Uploading to GCS and creating sha1 files'
upload_to_google_storage.py --bucket=chromium-clang-format buildtools/linux64/clang-format
upload_to_google_storage.py --bucket=chromium-clang-format buildtools/win/clang-format.exe
upload_to_google_storage.py --bucket=chromium-clang-format buildtools/mac/clang-format.x64
upload_to_google_storage.py --bucket=chromium-clang-format buildtools/mac/clang-format.arm64

# Clean up
rm /tmp/clang-format-$CLANG_REV.tgz
# These aren't in .gitignore because these mac per-arch paths only exist when updating clang-format.
# gclient runhooks puts these binaries at buildtools/mac/clang-format.
rm buildtools/mac/clang-format.x64 buildtools/mac/clang-format.arm64

Check that the new clang-format works as expected

Compare the diffs created by running the old and new clang-format versions to see if the new version does anything unexpected. Running them on some substantial directory like third_party/blink or base should be sufficient. Upload the diffs as two patchsets in a CL for easy inspection of the clang-format differences by choosing patchset 1 as the base for the gerrit diff.

## New gerrit CL with results of old clang-format.
# use old clang-format
find base -name '*.cc' -o -name '*.c' -o -name '*.h' -o -name '*.mm' | xargs ./buildtools/linux64/clang-format -i
git commit -a
git cl upload --bypass-hooks
## New patchset on gerrit CL with results of new clang-format.
# update to new clang-format
find base -name '*.cc' -o -name '*.c' -o -name '*.h' -o -name '*.mm' | xargs ./buildtools/linux64/clang-format -i
git commit -a --amend --no-edit
git cl upload --bypass-hooks

If there are any unexpected diffs, file a bug upstream (and fix it if you can :)).

Upload a CL according to the following template

Update clang-format binaries and scripts for all platforms.

I followed these instructions:
https://chromium.googlesource.com/chromium/src/+/main/docs/updating_clang_format_binaries.md

The binaries were built at clang revision ####### on ##CRREV##.

Diff on base/ from previous revision of clang-format to this version:
https://crrev.com/c/123123123/1..2

Bug: #######

The change should always include new .sha1 files for each platform (we want to keep these in lockstep), should never include clang-format binaries directly. The change should always update README.chromium

clang-format binaries should weigh in at 1.5MB or less. Watch out for size regressions.