ktfmt
ktfmt
is a program that pretty-prints (formats) Kotlin code, based on google-java-format.
Note that ktfmt
still has some rough edges which we're constantly working on fixing.
The minimum supported runtime version is JDK 11, released September 2018.
Demo
Before Formatting | Formatted by ktfmt |
---|---|
For comparison, the same code formatted by ktlint
and IntelliJ:
Formatted by ktlint |
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...]
--dropbox-style
makes 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.
Spotless
usingOn 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
FAQ
ktfmt
vs 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.
In particular,
ktfmt
ignores most existing formatting. It respects existing newlines in some places, but in general, its output is determinstic and is independent of the input code.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.
These two properties make ktfmt
a good fit in large Kotlin code bases, where consistency is very important.
We 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 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.
Developer's Guide
Setup
- 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 google/google-java-format#417)
Development
- Currently, we mainly develop by adding tests to
FormatterKtTest.kt
.
Building on the Command Line
- Run
mvn install
- Run
java -jar core/target/ktfmt-<VERSION>-jar-with-dependencies.jar
Releasing
See RELEASING.md.
License
Apache License 2.0