ktfmt

ktfmt is a program that pretty-prints (formats) Kotlin code, based on google-java-format.

Before

  private fun declareOne(      kind: DeclarationKind,      modifiers: KtModifierList? = null,      valOrVarKeyword: String? = null,      typeParameters: KtTypeParameterList? = null,
      receiver: KtTypeReference? = null,     name: String? = "",      type: KtTypeReference? = null,      op: String = "",      equals: String = "=",
      typeConstraintList: KtTypeConstraintList? = null,      initializer: PsiElement? = null,
      delegate: KtPropertyDelegate? = null,      trailing: String? = null
  ): Int {
//
}

After

private fun declareOne(
    kind: DeclarationKind,
    modifiers: KtModifierList? = null,
    valOrVarKeyword: String? = null,
    typeParameters: KtTypeParameterList? = null,
    receiver: KtTypeReference? = null,
    name: String? = "",
    type: KtTypeReference? = null,
    op: String = "",
    equals: String = "=",
    typeConstraintList: KtTypeConstraintList? = null,
    initializer: PsiElement? = null,
    delegate: KtPropertyDelegate? = null,
    trailing: String? = null
): Int {
  //
}

Note that ktfmt still has some rough edges which we're constantly working on fixing.

Using on the command-line

Make sure the vendor/google-java/format submodule is populated. Either clone with submodules (git pull --recurse-submodules https://github.com/facebookincubator/ktfmt.git) or populate the submodule after cloning (git submodule update --init)
Run mvn install
Run java -jar core/target/ktfmt-0.1-SNAPSHOT-jar-with-dependencies.jar

FAQ

`ktfmt` uses a 2-space indent; why not 4?

Two reasons -

Many of our projects use a mixture of Kotlin and Java, and we found the back-and-forth in styles to be distracting.
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.

Developer's Guide

Setup

Make sure the vendor/google-java/format submodule is populated. Either clone with submodules (git pull --recurse-submodules https://github.com/facebookincubator/ktfmt.git) or populate the submodule after cloning (git submodule update --init)
Open pom.xml in IntelliJ. Choose “Open as a Project”
The IntelliJ project will unfortunately be broken on import. To fix,
- 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)
- Right click on “vendor/google-java-format/pom.xml” and choose “Add maven project”

Development

Currently, we mainly develop by adding tests to FormatterKtTest.kt.

License

Apache License 2.0