Contributing to Mercury's Buck2 fork (mercury-head)

This repo is Mercury's internal fork of Buck2. The mercury-head branch is our maintained head.

Workflow

1. Branch from mercury-head

git fetch origin
git checkout -b my-feature origin/mercury-head

2. Make a PR to mercury-head

Open a pull request targeting the mercury-head branch (not main).

3. After merging, create a tag

Once your PR is merged, tag the new mercury-head HEAD using the format:

mwb-<date>-base-<fb-base-tag>

Where:

• <date> is today's date in YYYY-MM-DD format
• <fb-base-tag> is the date tag of the FB upstream commit that mercury is currently based on (e.g. 2026-01-19)

Example:

# Find the current mercury HEAD
git fetch origin
git rev-parse origin/mercury-head

# Create and push the tag
git tag mwb-2026-03-25-base-2026-01-19 origin/mercury
git push origin mwb-2026-03-25-base-2026-01-19

To find the correct <fb-base-tag>: look at the FB upstream tags in this repo (e.g. 2026-01-19, 2026-03-15) and identify which one the current mercury-head branch is based on.

4. Update buck2-source in mwb

In the mercury-web-backend repo, update the buck2-source reference to point to your new tag.