v8/docs/merging_and_patching.md

Introduction

If you have a patch to the master branch (e.g. an important bug fix) that needs to be merged into one of the production V8 branches, read on.

For the examples, a branched 2.4 version of V8 will be used. Substitute "2.4" with your version number.

An associated issue on Chromium's or V8's issue tracker is mandatory if a patch is merged. This helps with keeping track of merges. You can use a template to create an issue.

Merge process outlined

The merge process in the Chromium and V8 tracker is driven by labels in the form of

Merge-[Status]-[Branch]

The currently important labels for V8 are:

1. Merge-Request-## initiates the process => This fix should be merged into M-##
2. Merge-Review-## The merge is not approved yet for M-## e.g. because Canary coverage is missing
3. Merge-Approved-## => Simply means that the Chrome TPM are signing the merge off
4. Merge-Merged-BRANCHNUMBER => When the merge is done the Merge-Approved label is swapped with this one. BRANCHNUMBER is the name/number of the V8 branch e.g. 4.3 for M-43.

Instructions for git using the automated script

How to check if a commit was already merged/reverted

Use mergeinfo.py to get all the commits which are connected to the HASH according to Git.

tools/release/mergeinfo.py HASH

Step 1: Run the script

Let's assume you're merging revision af3cf11 to branch 2.4 (please specify full git hashes - abbreviations are used here for simplicity).

tools/release/merge_to_branch.py --branch 2.4 af3cf11

Run the script with '-h' to display its help message, which includes more options (e.g. you can specify a file containing your patch, or you can reverse a patch, specify a custom commit message, or resume a merging process you've canceled before). Note that the script will use a temporary checkout of v8 - it won't touch your work space. You can also merge more than one revision at once, just list them all.

tools/release/merge_to_branch.py --branch 2.4 af3cf11 cf33f1b sf3cf09

Step 2: Send a notification letter to hablich@chromium.org

Saying something like this:

_Subject:_ Regression fix merged into V8 2.4 branch (Chrome 8)

_Body:_ We have merged a fix to the V8 version 2.4 branch (the version used in Chrome 8)

Version 2.4.9.10: Issue xxx: The parser doesn't parse.

FAQ

I get an error during merge that is related to tagging. What should I do?

When two people are merging at the same time a race-condition can happen in the merge scripts. If this is the case, contact machenbach@chromium.org and hablich@chromium.org.

Is there a TL;DR;?

1. Create issue on issue tracker
2. Add Merge-Request-{Branch} to the issue
3. Wait until somebody will add Merge-Approved-{Branch}
4. Merge