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 is mandatory if a patch is merged. This helps with keeping track of merges.

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