1# ktfmt [](https://github.com/facebook/ktfmt/releases/) [](https://central.sonatype.com/artifact/com.facebook/ktfmt) [](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 4[google-java-format](https://github.com/google/google-java-format). 5 6The minimum supported runtime version is JDK 11, released September 2018. 7 8## Demo 9 10|Before Formatting| Formatted by `ktfmt`| 11| ---- | ---- | 12|  |  | 13 14For comparison, the same code formatted by [`ktlint`](https://github.com/pinterest/ktlint) and 15IntelliJ: 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 24would format your code. 25Give it a try! https://facebook.github.io/ktfmt/ 26 27## Using the formatter 28 29### IntelliJ, Android Studio, and other JetBrains IDEs 30 31A [ktfmt IntelliJ plugin](https://plugins.jetbrains.com/plugin/14912-ktfmt) is available from the 32plugin repository. To install it, go to your IDE's settings and select the `Plugins` category. Click 33the `Marketplace` tab, search for the `ktfmt` plugin, and click the `Install` button. 34 35The plugin will be disabled by default. To enable it in the current project, go to 36`File → Settings... → ktfmt Settings` (or `IntelliJ IDEA → Preferences... → Editor → ktfmt Settings` 37on macOS) and check the `Enable ktfmt` checkbox. A notification will be presented when you first 38open a project offering to do this for you. 39 40To enable it by default in new projects, use 41`File → New Project Settings → Preferences for new Projects → Editor → ktfmt Settings`. 42 43When enabled, it will replace the normal `Reformat Code` action, which can be triggered from the 44`Code` menu or with the Ctrl-Alt-L (by default) keyboard shortcut. 45 46To configure IntelliJ to approximate ktfmt's formatting rules during code editing, you can edit your 47project's 48[`.editorconfig` file](https://www.jetbrains.com/help/idea/configuring-code-style.html#editorconfig) 49to include the Kotlin section from one of the files inside [`docs/editorconfig`](docs/editorconfig). 50 51#### Share IntelliJ ktfmt settings 52In order to share the settings, make sure to commit the file `.idea/ktfmt.xml` into your codebase. 53 54### Installation 55 56#### Homebrew 57 58If you're a [Homebrew](https://brew.sh) user, you can install 59[ktfmt](https://formulae.brew.sh/formula/ktfmt) via: 60 61``` 62$ brew install ktfmt 63``` 64 65### from the command-line 66 67[Download the formatter](https://github.com/facebook/ktfmt/releases) and run it with: 68 69``` 70java -jar /path/to/ktfmt-<VERSION>-jar-with-dependencies.jar [--kotlinlang-style | --google-style] [files...] 71``` 72 73`--kotlinlang-style` makes `ktfmt` use a block indent of 4 spaces instead of 2. 74See below for details. 75 76***Note:*** 77*There is no configurability as to the formatter's algorithm for formatting (apart from the 78different styles). This is a deliberate design decision to unify our code formatting on a single 79format.* 80 81### using Gradle 82 83A [Gradle plugin (ktfmt-gradle)](https://github.com/cortinico/ktfmt-gradle) is available on the 84Gradle Plugin Portal. To set it up, just follow the instructions in the 85[How-to-use section](https://github.com/cortinico/ktfmt-gradle#how-to-use-). 86 87Alternatively, you can use [Spotless](https://github.com/diffplug/spotless) with the 88[ktfmt Gradle plugin](https://github.com/diffplug/spotless/tree/main/plugin-gradle#ktfmt). 89 90### using Maven 91 92Consider using [Spotless](https://github.com/diffplug/spotless) with the 93[ktfmt Maven plugin](https://github.com/diffplug/spotless/tree/main/plugin-maven#ktfmt). 94 95### using pre-commit hooks 96 97A [pre-commit hook](https://pre-commit.com/hooks.html) is implemented in 98[language-formatters-pre-commit-hooks](https://github.com/macisamuele/language-formatters-pre-commit-hooks) 99 100## FAQ 101 102### `ktfmt` vs `ktlint` vs IntelliJ 103 104`ktfmt` uses google-java-format's underlying engine, and as such, many items on 105[google-java-format's FAQ](https://github.com/google/google-java-format/wiki/FAQ) apply to `ktfmt` 106as well. 107 108In particular, here are the principles that we try to adhere to: 1091. `ktfmt` ignores most existing formatting. It respects existing newlines in some places, but in 110 general, its output is deterministic and is independent of the input code. 1112. `ktfmt` exposes no configuration options that govern formatting behavior. See 112 https://github.com/google/google-java-format/wiki/FAQ#i-just-need-to-configure-it-a-bit-differently-how 113 for the rationale. 114 1. For exposed configurations, like `style`, we aim to make sure that those are easily shared 115 across your organization/codebase to avoid 116 [bikeshedding discussions](https://thedecisionlab.com/biases/bikeshedding) about code format. 117 118These two properties make `ktfmt` a good fit in large Kotlin code bases, where consistency is very 119important. 120 121We created `ktfmt` because at the time `ktlint` and IntelliJ sometimes failed to produce 122nice-looking code that fits in 100 columns, as can be seen in the [Demo](README.md#Demo) section. 123 124### `ktfmt` uses a 2-space indent; why not 4? any way to change that? 125 126Two reasons - 1271. Many of our projects use a mixture of Kotlin and Java, and we found the back-and-forth in styles 128 to be distracting. 1292. From a pragmatic standpoint, the formatting engine behind google-java-format uses more whitespace 130 and newlines than other formatters. Using an indentation of 4 spaces quickly reaches the maximal 131 column width. 132 133However, we do offer an alternative style for projects that absolutely cannot make the move to 134`ktfmt` because of 2-space: the style `--kotlinlang-style` changes block indents to 4-space. 135 136## Developer's Guide 137 138### Setup 139 140* Open `pom.xml` in IntelliJ. Choose "Open as a Project" 141* The IntelliJ project will unfortunately be broken on import. To fix, 142 * Turn off ErrorProne by removing the compiler parameters in IntelliJ at the bottom of 143 `Settings → Build, Execution, Deployment → Compiler → Java Compiler` (see 144 https://github.com/google/google-java-format/issues/417) 145 146### Development 147 148* Currently, we mainly develop by adding tests to `FormatterTest.kt`. 149 150### Building on the Command Line 151 152* Run `mvn install` 153* Run `java -jar core/target/ktfmt-<VERSION>-jar-with-dependencies.jar` 154 155### Releasing 156 157See [RELEASING.md](RELEASING.md). 158 159## License 160 161Apache License 2.0 162
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