docs/code_reviews.md

# Code Reviews

Code reviews are a central part of developing high-quality code for Chromium.
All changes must be reviewed.

The general patch, upload, and land process is covered in more detail in the
[contributing code](contributing.md) page.

# Code review policies

Ideally the reviewer is someone who is familiar with the area of code you are
touching. Any committer can review code, but an owner must provide a review
for each directory you are touching. If you have doubts, look at the git blame
for the file and the `OWNERS` files (see below).

To indicate a positive review, the reviewer provides a "Code-Review +1" in
Gerrit, also known as an LGTM ("Looks Good To Me"). A score of "-1" indicates
the change should not be submitted as-is.

If you have multiple reviewers, provide a message indicating what you expect
from each reviewer. Otherwise people might assume their input is not required
or waste time with redundant reviews.

Please also read [Respectful Changes](cl_respect.md) and
[Respectful Code Reviews](cr_respect.md).

#### Expectations for all reviewers

  * Aim to provide some kind of actionable response within 24 hours of receipt
    (not counting weekends and holidays). This doesn't mean you have to do a
    complete review, but you should be able to give some initial feedback,
    request more time, or suggest another reviewer.

  * Use the status field in Gerrit settings to indicate if you're away and when
    you'll be back.

  * Don't generally discourage people from sending you code reviews. This
    includes using a blanket "slow" in your status field.

## OWNERS files

In various directories there are files named `OWNERS` that list the email
addresses of people qualified to review changes in that directory. You must
get a positive review from an owner of each directory your change touches.

Owners files are recursive, so each file also applies to its subdirectories.
It's generally best to pick more specific owners. People listed in higher-level
directories may have less experience with the code in question. For example,
the reviewers in the `//chrome/browser/component_name/OWNERS` file will likely
be more familiar with code in `//chrome/browser/component_name/sub_component`
than reviewers in the higher-level `//chrome/OWNERS` file.

More detail on the owners file format is provided in the "More information"
section below.

*Tip:* The `git cl owners` command can help find owners.

While owners must approve all patches, any committer can contribute to the
review. In some directories the owners can be overloaded or there might be
people not listed as owners who are more familiar with the low-level code in
question. In these cases it's common to request a low-level review from an
appropriate person, and then request a high-level owner review once that's
complete. As always, be clear what you expect of each reviewer to avoid
duplicated work.

Owners do not have to pick other owners for reviews. Since they should already
be familiar with the code in question, a thorough review from any appropriate
committer is sufficient.

#### Expectations of owners

The existing owners of a directory approve additions to the list. It is
preferable to have many directories, each with a smaller number of specific
owners rather than large directories with many owners. Owners should:

  * Demonstrate excellent judgment, teamwork and ability to uphold Chrome
    development principles.

  * Be already acting as an owner, providing high-quality reviews and design
    feedback.

  * Be a Chromium project member with full commit access of at least three
    months tenure.

  * Have submitted a substantial number of non-trivial changes to the affected
    directory.

  * Have committed or reviewed substantial work to the affected directory
    within the last ninety days.

  * Have the bandwidth to contribute to reviews in a timely manner. If the load
    is unsustainable, work to expand the number of owners. Don't try to
    discourage people from sending reviews, including writing "slow" or
    "emeritus" after your name.

The above are guidelines more than they are hard rules, and exceptions are
okay as long as there is a consensus by the existing owners for them.
For example, seldom-updated directories may have exceptions to the
"substantiality" and "recency" requirements. Directories in `third_party`
should list those most familiar with the library, regardless of how often
the code is updated.

### OWNERS file details

Refer to the [source code](https://chromium.googlesource.com/chromium/tools/depot_tools/+/master/owners.py)
for all details on the file format.

This example indicates that two people are owners, in addition to any owners
from the parent directory. `git cl owners` will list the comment after an
owner address, so this is a good place to include restrictions or special
instructions.
```
# You can include comments like this.