xref: /third_party/skia/site/docs/dev/contrib/patch.md

---
title: 'Applying patches'
linkTitle: 'Applying patches'
---

If you are a Skia committer and have been asked to commit an
externally-submitted patch, this is how to do it. (This technique is useful in
other situations too, like if you just want to try out somebody else's patch
locally.)

Notes:

- For the examples below, we will assume that this is the change you want to
  patch into your local checkout: https://codereview.appspot.com/6201055/
- These instructions should work on Mac or Linux; Windows is trickier, because
  there is no standard Windows "patch" tool.

See also [Contributing Code for The Chromium Projects]
(http://dev.chromium.org/developers/contributing-code#TOC-Instructions-for-Reviewer:-Checking-in-the-patch-for-a-non-committer).

If you use `git cl`, then you should be able to use the shortcut:

```
git cl patch 6201055
```

If you use `gcl`, or the above doesn't work, the following should always work.

1. Prepare your local workspace to accept the patch.

   - cd into the root directory (usually `trunk/`) of the workspace where you
     want to apply the patch.
   - Make sure that the workspace is up-to-date and clean (or "updated and clean
     enough" for your purposes). If the codereview patch was against an old
     revision of the repo, you may need to sync your local workspace to that
     same revision.

2. Download the raw patch set.

   - Open the codereview web page and look for the "Download raw patch set" link
     near the upper right-hand corner. Right-click on that link and copy it to
     the clipboard. (In my case, the link is
     https://codereview.appspot.com/download/issue6201055_1.diff )
   - If you are on Linux or Mac and have "curl" or "wget" installed, you can
     download the patch from the command line:

   ```
   curl https://codereview.appspot.com/download/issue6201055_1.diff
   --output patch.txt
   # or...
   wget https://codereview.appspot.com/download/issue6201055_1.diff
   --output-document=patch.txt
   ```

   - Otherwise, figure out some other way to download this file and save it as
     `patch.txt`

3. Apply this patch to your local checkout.

   - You should still be in the root directory of the workspace where you want
     to apply the patch.

   ```
   patch -p1 <patch.txt
   ```

   - Then you can run `diff` and visually check the local changes.

4. Complications: If the patch fails to apply, the following may be happening:

   - Wrong revision. Maybe your local workspace is not up to date? Or maybe the
     patch was made against an old revision of the repository, and cannot be
     applied to the latest revision? (In that case, revert any changes and sync
     your workspace to an older revision, then re-apply the patch.)