= Patch Sets

As described in link:concept-changes.html[Changes], a change represents a single
commit under review. Each change is assigned a
link:concept-changes.html#change-id[Change-Id].

It is very common to amend a commit during the code review process. Gerrit uses
the Change-Id to associate each iteration of the commit with the same change.
These iterations of a commit are referred to as _patch sets_. When a change is
approved, only the latest version of a commit is submitted to the repository.

NOTE: It is also possible to copy a Change-Id to a completely new commit. This
is useful in situations where you want to keep the discussion around a change,
but also need to completely modify your approach.

== File List

When you open a change in Gerrit, a list of affected files appears in the
file list, located in the middle of the Review screen. This table displays
the following information for each file:

* A checkbox, indicating the file has been reviewed
* The type of modification
* The path and name of the file
* The number of added lines and or deleted lines

[[file-modifications]]
== File modifications

Each file in a patch set has a letter next to it, indicating the type of
modification for that file. The following table lists the types of
modifications.

.Types of file modifications
|===
|Letter|Modification Type|Definition

|M
|Modification
|The file existed before this change and is modified.

|A
|Added
|The file is newly added.

|D
|Deleted
|The file is deleted.

|R
|Renamed
|The file is renamed.

|C
|Copied
|The file is new and is copied from an existing file.

|===

If the status is *R* (Renamed) or *C* (Copied), the file list also displays the
original name of the file below the patch set file.

== Views

By default, Gerrit displays the latest patch set for a given change. You can
view previous versions of a patch set by selecting from the *Patch Set*
drop-down list.

== Diffs

Clicking a file in the file list opens the Diff screen. By default, this
screen displays a diff between the latest patch set's version of a file and the
current version of that file in the repository. You can also open a diff within
the Review screen by clicking the blue triangle located in the same row as the
file. To show the diffs of all files in the Review screen, click the *Show
Diffs* link, located at the top of the file list.

You can diff between other patch sets by selecting a patch set number from the
*Diff Against* drop-down list.

== Description

Each change in Gerrit must have a change description. This change description
comes from the commit message and becomes part of the history of the project.

In addition to the change description, you can add a description for a specific
patch set. This description is intended to help guide reviewers as a change
evolves, such as "Added more unit tests." Unlike the change description, a patch
set description does not become a part of the project's history.

To add a patch set description, click *Add a patch set description*, located in
the file list.

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