README.md
1# ktfmt [](https://github.com/facebook/ktfmt/releases/) [](https://github.com/facebook/ktfmt/actions/workflows/build_and_test.yml "GitHub Actions workflow status") [](https://slack-chats.kotlinlang.org/c/ktfmt) [](https://surveys.jetbrains.com/s3/kotlin-slack-sign-up) [](https://github.com/facebook/ktfmt/issues)
2
3`ktfmt` is a program that pretty-prints (formats) Kotlin code, based on [google-java-format](https://github.com/google/google-java-format).
4
5**Note** that `ktfmt` still has some rough edges which we're constantly working on fixing.
6
7The minimum supported runtime version is JDK 11, released September 2018.
8
9## Demo
10
11|Before Formatting| Formatted by `ktfmt`|
12| ---- | ---- |
13|  |  |
14
15For comparison, the same code formatted by [`ktlint`](https://github.com/pinterest/ktlint) and IntelliJ:
16
17| Formatted by `ktlint`|Formatted by IntelliJ|
18| ------ | --------|
19|  |  |
20
21## Playground
22
23We have a [live playground](https://facebook.github.io/ktfmt/) where you can easily see how ktfmt would format your code.
24Give it a try! https://facebook.github.io/ktfmt/
25
26## Using the formatter
27
28### IntelliJ, Android Studio, and other JetBrains IDEs
29
30A
31[ktfmt IntelliJ plugin](https://plugins.jetbrains.com/plugin/14912-ktfmt)
32is available from the plugin repository. To install it, go to your IDE's
33settings and select the `Plugins` category. Click the `Marketplace` tab, search
34for the `ktfmt` plugin, and click the `Install` button.
35
36The plugin will be disabled by default. To enable it in the current project, go
37to `File→Settings...→ktfmt Settings` (or `IntelliJ
38IDEA→Preferences...→Editor→ktfmt Settings` on macOS) and
39check the `Enable ktfmt` checkbox. (A notification will be
40presented when you first open a project offering to do this for you.)
41
42To enable it by default in new projects, use `File→New Project Settings→Preferences for new Projects→Editor→ktfmt Settings`.
43
44When enabled, it will replace the normal `Reformat Code` action, which can be
45triggered from the `Code` menu or with the Ctrl-Alt-L (by default) keyboard
46shortcut.
47
48To configure IntelliJ to approximate ktfmt's formatting rules during code editing,
49you can edit your project's
50[`.editorconfig` file](https://www.jetbrains.com/help/idea/configuring-code-style.html#editorconfig)
51to include the Kotlin section from one of the files inside
52[`docs/editorconfig`](docs/editorconfig).
53Not all of ktfmt's rules can be represented as IntelliJ editor settings, so you will still
54need to run ktfmt. Alternately, that file can be used as a reference to manually change
55the project's code style settings.
56
57### Installation
58
59#### Homebrew
60
61If you're a [Homebrew](https://brew.sh) user, you can install [ktfmt](https://formulae.brew.sh/formula/ktfmt) via:
62
63```
64$ brew install ktfmt
65```
66
67### from the command-line
68
69[Download the formatter](https://github.com/facebook/ktfmt/releases)
70and run it with:
71
72```
73java -jar /path/to/ktfmt-<VERSION>-jar-with-dependencies.jar [--dropbox-style] [files...]
74```
75
76`--dropbox-style` makes `ktfmt` use a block indent of 4 spaces instead of 2. See below for details.
77
78***Note:*** *There is no configurability as to the formatter's algorithm for
79formatting (apart from `--dropbox-style`). This is a deliberate design decision to unify our code
80formatting on a single format.*
81
82### using Gradle
83
84A [Gradle plugin (ktfmt-gradle)](https://github.com/cortinico/ktfmt-gradle) is available on the Gradle Plugin Portal. To set it up, just follow the instructions in the [How-to-use section](https://github.com/cortinico/ktfmt-gradle#how-to-use-).
85
86Alternatively, you can use [Spotless](https://github.com/diffplug/spotless) with the [ktfmt Gradle plugin](https://github.com/diffplug/spotless/tree/main/plugin-gradle#ktfmt).
87
88### using Maven
89
90Consider using [Spotless](https://github.com/diffplug/spotless) with the [ktfmt Maven plugin](https://github.com/diffplug/spotless/tree/main/plugin-maven#ktfmt).
91
92### using pre-commit hooks
93
94A [pre-commit hook](https://pre-commit.com/hooks.html) is implemented in [language-formatters-pre-commit-hooks](https://github.com/macisamuele/language-formatters-pre-commit-hooks)
95
96## FAQ
97
98### `ktfmt` vs `ktlint` vs IntelliJ
99
100`ktfmt` uses google-java-format's underlying engine, and as such, many items on [google-java-format's FAQ](https://github.com/google/google-java-format/wiki/FAQ) apply to `ktfmt` as well.
101
102In particular,
1031. `ktfmt` ignores most existing formatting. It respects existing newlines in some places, but in general, its output is deterministic and is independent of the input code.
1042. `ktfmt` exposes no configuration options that govern formatting behavior. See https://github.com/google/google-java-format/wiki/FAQ#i-just-need-to-configure-it-a-bit-differently-how for the rationale.
105
106These two properties make `ktfmt` a good fit in large Kotlin code bases, where consistency is very important.
107
108We created `ktfmt` because `ktlint` and IntelliJ sometime fail to produce nice-looking code that fits in 100 columns, as can be seen in the [Demo](README.md#Demo) section.
109
110### `ktfmt` uses a 2-space indent; why not 4? any way to change that?
111
112Two reasons -
1131. Many of our projects use a mixture of Kotlin and Java, and we found the back-and-forth in styles to be distracting.
1142. From a pragmatic standpoint, the formatting engine behind google-java-format uses more whitespace and newlines than other formatters. Using an indentation of 4 spaces quickly reaches the maximal column width.
115
116However, we do offer an escape-hatch for projects that absolutely cannot make the move to `ktfmt` because of 2-space: the `--dropbox-style` flag changes block indents to 4-space.
117
118## Developer's Guide
119
120### Setup
121
122* Open `pom.xml` in IntelliJ. Choose "Open as a Project"
123* The IntelliJ project will unfortunately be broken on import. To fix,
124 * Turn off ErrorProne by removing the compiler parameters in IntelliJ at the bottom of "Settings -> Build, Execution, Deployment -> Compiler -> Java Compiler" (see https://github.com/google/google-java-format/issues/417)
125
126### Development
127
128* Currently, we mainly develop by adding tests to `FormatterTest.kt`.
129
130### Building on the Command Line
131
132* Run `mvn install`
133* Run `java -jar core/target/ktfmt-<VERSION>-jar-with-dependencies.jar`
134
135### Releasing
136
137See [RELEASING.md](RELEASING.md).
138
139## License
140
141Apache License 2.0
142
){kind=link}
){kind=link}
