ktfmt is a program that pretty-prints (formats) Kotlin code, based on google-java-format.
ktfmt still has some rough edges which we're constantly working on fixing.
The minimum supported runtime version is JDK 11, released September 2018.
|Before Formatting||Formatted by
For comparison, the same code formatted by
ktlint and IntelliJ:
||Formatted by IntelliJ|
Using the formatter
from the command-line
Download the formatter and run it with:
java -jar /path/to/ktfmt-<VERSION>-jar-with-dependencies.jar [--dropbox-style] [files...]
ktfmt use a block indent of 4 spaces instead of 2. See below for details.
Note: There is no configurability as to the formatter's algorithm for formatting (apart from
--dropbox-style). This is a deliberate design decision to unify our code formatting on a single format.
On Gradle: https://github.com/diffplug/spotless/tree/master/plugin-gradle#applying-ktfmt-to-kotlin-files On Maven: https://github.com/diffplug/spotless/tree/master/plugin-maven#applying-ktfmt-to-kotlin-files
ktlint vs IntelliJ
ktfmt uses google-java-format's underlying engine, and as such, many items on google-java-format's FAQ apply to
ktfmt as well.
ktfmtignores most existing formatting. It respects existing newlines in some places, but in general, its output is determinstic and is independent of the input code.
ktfmtexposes 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.
These two properties make
ktfmt a good fit in large Kotlin code bases, where consistency is very important.
ktlint and IntelliJ sometime fail to produce nice-looking code that fits in 100 columns, as can be seen in the Demo section.
ktfmt uses a 2-space indent; why not 4? any way to change that?
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.
However, 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.
pom.xmlin 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)
- Currently, we mainly develop by adding tests to
Building on the Command Line
java -jar core/target/ktfmt-<VERSION>-jar-with-dependencies.jar
Apache License 2.0