1[](https://github.com/facebookincubator/ktfmt/actions?query=workflow%3Abuild) 2 3# ktfmt 4 5`ktfmt` is a program that pretty-prints (formats) Kotlin code, based on [google-java-format](https://github.com/google/google-java-format). 6 7**Note** that `ktfmt` still has some rough edges which we're constantly working on fixing. 8 9The minimum supported runtime version is JDK 11, released September 2018. 10 11## Demo 12 13|Before Formatting| Formatted by `ktfmt`| 14| ---- | ---- | 15|  |  | 16 17For comparison, the same code formatted by [`ktlint`](https://github.com/pinterest/ktlint) and IntelliJ: 18 19| Formatted by `ktlint`|Formatted by IntelliJ| 20| ------ | --------| 21|  |  | 22 23## Using the formatter 24 25### IntelliJ, Android Studio, and other JetBrains IDEs 26 27A 28[ktfmt IntelliJ plugin](https://plugins.jetbrains.com/plugin/14912-ktfmt) 29is available from the plugin repository. To install it, go to your IDE's 30settings and select the `Plugins` category. Click the `Marketplace` tab, search 31for the `ktfmt` plugin, and click the `Install` button. 32 33The plugin will be disabled by default. To enable it in the current project, go 34to `File→Settings...→ktfmt Settings` (or `IntelliJ 35IDEA→Preferences...→Editor→ktfmt Settings` on macOS) and 36check the `Enable ktfmt` checkbox. (A notification will be 37presented when you first open a project offering to do this for you.) 38 39To enable it by default in new projects, use `File→New Project Settings→Preferences for new Projects→Editor→ktfmt Settings`. 40 41When enabled, it will replace the normal `Reformat Code` action, which can be 42triggered from the `Code` menu or with the Ctrl-Alt-L (by default) keyboard 43shortcut. 44 45To configure IntelliJ to approximate ktfmt's formatting rules during code editing, 46you can edit your project's 47[`.editorconfig` file](https://www.jetbrains.com/help/idea/configuring-code-style.html#editorconfig) 48to include the Kotlin section from one of the files inside 49[`docs/editorconfig`](docs/editorconfig). 50Not all of ktfmt's rules can be represented as IntelliJ editor settings, so you will still 51need to run ktfmt. Alternately, that file can be used as a reference to manually change 52the project's code style settings. 53 54### from the command-line 55 56[Download the formatter](https://github.com/facebookincubator/ktfmt/releases) 57and run it with: 58 59``` 60java -jar /path/to/ktfmt-<VERSION>-jar-with-dependencies.jar [--dropbox-style] [files...] 61``` 62 63`--dropbox-style` makes `ktfmt` use a block indent of 4 spaces instead of 2. See below for details. 64 65***Note:*** *There is no configurability as to the formatter's algorithm for 66formatting (apart from `--dropbox-style`). This is a deliberate design decision to unify our code 67formatting on a single format.* 68 69### using Gradle 70 71A [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-). 72 73Alternatively, you can use [Spotless](https://github.com/diffplug/spotless) with the [ktfmt Gradle plugin](https://github.com/diffplug/spotless/tree/main/plugin-gradle#ktfmt). 74 75### using Maven 76 77Consider using [Spotless](https://github.com/diffplug/spotless) with the [ktfmt Maven plugin](https://github.com/diffplug/spotless/tree/main/plugin-maven#ktfmt). 78 79## FAQ 80 81### `ktfmt` vs `ktlint` vs IntelliJ 82 83`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. 84 85In particular, 861. `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. 872. `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. 88 89These two properties make `ktfmt` a good fit in large Kotlin code bases, where consistency is very important. 90 91We 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. 92 93### `ktfmt` uses a 2-space indent; why not 4? any way to change that? 94 95Two reasons - 961. Many of our projects use a mixture of Kotlin and Java, and we found the back-and-forth in styles to be distracting. 972. 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. 98 99However, 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. 100 101## Developer's Guide 102 103### Setup 104 105* Open `pom.xml` in IntelliJ. Choose "Open as a Project" 106* The IntelliJ project will unfortunately be broken on import. To fix, 107 * 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) 108 109### Development 110 111* Currently, we mainly develop by adding tests to `FormatterTest.kt`. 112 113### Building on the Command Line 114 115* Run `mvn install` 116* Run `java -jar core/target/ktfmt-<VERSION>-jar-with-dependencies.jar` 117 118### Releasing 119 120See [RELEASING.md](RELEASING.md). 121 122## License 123 124Apache License 2.0 125
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