Scala source code formatter
Scala
Latest commit f53978c Oct 18, 2016 @dragos dragos committed on GitHub Merge pull request #233 from SethTisue/be-2.12-compatible
update build to work with Scala 2.12

README.rst

Scalariform

Scalariform is a code formatter for Scala. It's available as a library, a stand-alone command line tool, or via integrations with various editors and build tools (listed below).

The plan is to add preferences and features as and when people ask for them, so please do raise a Github issue if it doesn't format your code the way you'd like it, and I'll see what I can do.

Scalariform is licenced under The MIT Licence.

Installing with Homebrew (for OS X users)

Mac OS X users can install the scalariform CLI tool using the Homebrew package manager.

brew install scalariform

Or, if you would like to install the latest development release:

brew install --HEAD scalariform

Packaging an executable JAR

If you would like to package scalariform for use on the command line with java -jar, clone the repo and perform the following simple steps:

sbt "project cli" "assembly"

sbt will build one jar with all the dependencies and put it in

cli/target/scala-$your_scala_version/cli-assembly-$scalariform_version.jar

You can copy this to a location in your path and execute it as follows:

java -jar /home/me/bin/cli-assembly-$scalariform_version.jar -f -q +compactControlReadability +alignParameters +alignSingleLineCaseStatements +doubleIndentClassDeclaration +rewriteArrowSymbols +preserveSpaceBeforeArguments --stdout ~/myproject/src/main/scala/Stuff.scala > Stuff.scala

Integration with sbt

A plugin for SBT is available at https://github.com/sbt/sbt-scalariform.

Usage within a project

Have a use for the scalariform source code directly? You can use it as a build dependency:

"org.scalariform" %% "scalariform" % "0.1.8"

Integration with Eclipse

Scala IDE for Eclipse uses Scalariform for code formatting:

  • Right click in the editor -> Source -> Format
  • Press Ctrl-Shift-F

If you select some lines, only those will be formatted.

You can also configure formatting to be run as a save action (Window -> Preferences -> Java -> Editor -> Save Actions).

To set preferences, go to either

  • Window -> Preferences -> Scala -> Editor -> Formatter
  • Project -> Properties -> Scala Formatter

Integration with Emacs/ENSIME

"ENSIME uses the Scalariform library to format Scala sources. Type C-c C-v f to format the current buffer."

Integration with jEdit

See ScalaSidekick by Stefan Ettrup:

Run Plugins -> scalaSidekickPlugin -> Format Scala File

Integration with Maven

There is a Maven plugin to run Scalariform contributed by Adam Crain on scala-tools.

Usage:

<plugin>
  <groupId>org.scalariform</groupId>
  <artifactId>scalariform-maven-plugin</artifactId>
  <version>0.1.4</version>
  <executions>
    <execution>
      <phase>process-sources</phase>
      <goals>
        <goal>format</goal>
      </goals>
      <configuration>
        <rewriteArrowSymbols>true</rewriteArrowSymbols>
      </configuration>
    </execution>
  </executions>
</plugin>

Integration with Gradle

There is a Gradle plugin to run Scalariform contributed by Jeroen van Erp.

Usage (Gradle 2.1 and above):

plugins {
  id "com.github.hierynomus.scalariform" version "0.1.0"
}

// optionally, configure Scalariform settings
scalariform {
  alignParameters = true
  alignSingleLineCaseStatements = true
}

formatAllScala

See the documentation for further usage examples.

Integration with TextMate

See Mads Jensen's Scala TextMate bundle:

http://github.com/mads379/scala.tmbundle

Reformat using Ctrl-Shift-H.

Use with Vim

While there is no specific Vim integration at present, you can use Scalariform as an external formatter for the gg=G command by adding the following to .vimrc

au BufEnter *.scala setl formatprg=java\ -jar\ /home/me/bin/scalariform.jar\ -f\ -q\ +compactControlReadability\ +alignParameters\ +alignSingleLineCaseStatements\ +doubleIndentClassDeclaration\ +rewriteArrowSymbols\ +preserveSpaceBeforeArguments\ --stdin\ --stdout
au BufEnter *.scala setl equalprg=java\ -jar\ /home/me/bin/scalariform.jar\ -f\ -q\ +compactControlReadability\ +alignParameters\ +alignSingleLineCaseStatements\ +doubleIndentClassDeclaration\ +rewriteArrowSymbols\ +preserveSpaceBeforeArguments\ --stdin\ --stdout

You can create your own executable scalariform.jar by following the instructions at the top of this file, in "Packaging an executable JAR."

Command line tool

https://github.com/scala-ide/scalariform/wiki/Command-line-tool

Library

https://github.com/scala-ide/scalariform/wiki/Library

Preferences

alignParameters

Default: false

Align class/function parameters (modifiers and name, type, and defaults) in three columns.

For example, if false, then:

class Person(name: String,
  age: Int = 24,
  birthdate: Date,
  astrologicalSign: String = "libra",
  shoeSize: Int,
  favoriteColor: java.awt.Color
)

If true, then:

class Person(name:             String,
             age:              Int            = 24,
             birthdate:        Date,
             astrologicalSign: String         = "libra",
             shoeSize:         Int,
             favoriteColor:    java.awt.Color
)

This will also place the "implicit" keyword in parameters on its own line, whenever the parameter being formatted contains a newline:

For example, if false, then:

def formatBirthDate(
  implicit birthdate: Date = Date("11/11/11"),
  birthtime: Time
): DateTime

If true, then:

def formatBirthDate(
  implicit
  birthdate: Date = Date("11/11/11"),
  birthtime: Time
): DateTime

This option is disabled if indentWithTabs is true.

firstParameterOnNewline

Default: Force

Whether or not to place the first parameter for multi-line method or constructor definition on its own line.

If Force, first parameters will be on a new line:

abstract class Person(
  name: Int,
  age: String
) {
  def livesIn(
    city: String,
    state: String
  ): Boolean
}

If Prevent, first parameters will be on the definition line:

abstract class Person(name: Int,
  age: String
) {
  def livesIn(city: String,
    state: String
  ): Boolean
}

If Preserve, first parameters will stay where they are:

abstract class Person(name: Int,
  age: String
) {
  def livesIn(
    city: String,
    state: String
  ): Boolean
}

alignArguments

Default: false

Aligns multi-line arguments

For example, if false, then:

Cake(candles = 10,
  frostingFlavor = Vanilla,
  layerFlavor = Chocolate,
  iceCream = true
)

If true, then:

Cake(candles        = 10,
     frostingFlavor = Vanilla,
     layerFlavor    = Chocolate,
     iceCream       = true
)

This option is disabled if indentWithTabs is true.

firstArgumentOnNewline

Default: Force

Whether or not to place the first argument of multi-line function calls on its own line.

If Force, first arguments will be on a new line:

foo(
  1,
  2
)

bar(
  3,
  4
)

If Prevent, first arguments will be on function call line:

foo(1,
  2
)

bar(3,
  4
)

If Preserve, first arguments will stay where they are:

foo(
  1,
  2
)

bar(3,
  4
)

alignSingleLineCaseStatements

Default: false

Align the arrows of consecutive single-line case statements. For example, if true, then:

a match {
  case b => 1
  case ccc => 2
  case dd => 3
}

Is reformatted as:

a match {
  case b   => 1
  case ccc => 2
  case dd  => 3
}

This option is disabled if indentWithTabs is true.

alignSingleLineCaseStatements.maxArrowIndent

Default: 40

When alignSingleLineCaseStatements is true, this is a limit on the number of spaces that can be inserted before an arrow to align it with other case statements. This can be used to avoid very large gaps, e.g.:

a match {
  case Some(wibble, wobble) if wibble + wibble > wobble * wibble => 1
  case ccc                                                       => 2
}

compactControlReadability

Default: false

When compactControlReadability is true, then if/else and try/catch/finally control structures will be formatted using Compact Control Readability style

if (x == y) {
  foo()
}
else if (y == z) {
  bar()
}
else {
  baz()
}

try {
  foo()
}
catch {
  case _ => bar()
}
finally {
  baz()
}

compactStringConcatenation

Default: false

Omit spaces when formatting a '+' operator on String literals. For example, if false, then:

"Hello " + name + "!"

If true, then:

"Hello "+name+"!"

The Scala Style Guide recommends that operators, "should always be invoked using infix notation with spaces separated the target".

doubleIndentClassDeclaration

Default: false

With this set to true, class (and trait / object) declarations will be formatted as recommended by the Scala Style Guide. That is, if the declaration section spans multiple lines, it will be formatted so that either the parameter section or the inheritance section is doubly indented. This provides a visual distinction from the members of the class. For example:

class Person(
  name: String,
  age: Int,
  birthdate: Date,
  astrologicalSign: String,
  shoeSize: Int,
  favoriteColor: java.awt.Color)
    extends Entity
    with Logging
    with Identifiable
    with Serializable {
  def firstMethod = ...
}

Or:

class Person(
    name: String,
    age: Int,
    birthdate: Date,
    astrologicalSign: String,
    shoeSize: Int,
    favoriteColor: java.awt.Color) {
  def firstMethod = ...
}

doubleIndentMethodDeclaration

Default: false

With this set to true, method declarations will have an extra indentation added to their parameter list, if it spans multiple lines. This provides a visual distinction from the method body. For example:

def longMethodNameIsLong(paramOneNameIsLong: String, paramTwo: String,
    paramThreeNameIsReallyLong): Unit = {
  val startOfMethod = ...
}

Or:

def longMethodNameIsLong(
    paramOneNameIsLong: String,
    paramTwoNameIsLong: String,
    paramThreeNameIsLong): Unit = {
  val startOfMethod = ...
}

formatXml

Default: true

Format embedded XML literals; if false they will be left untouched.

indentLocalDefs

Default: false

If true, indent local methods an extra level, with the intention of distinguishing them from other statements. For example,:

class A {
  def find(...) = {
    val x = ...
      def find0() = {
        ...
      }
    find0(...)
  }
}

indentPackageBlocks

Default: true

Whether to indent package blocks. For example, if true:

package foo {
  package bar {
    class Baz
  }
}

Else if false:

package foo {
package bar {
class Baz
}
}

indentSpaces

Default: 2

The number of spaces to use for each level of indentation.

This option is ignored if indentWithTabs is true.

indentWithTabs

Default: false

Use a tab for each level of indentation. When set to true, this ignores any setting given for indentSpaces. In addition, for the moment, alignSingleLineCaseStatements, alignArguments, and alignParameters options are not supported when indenting with tabs, and XML indentation is handled differently.

multilineScaladocCommentsStartOnFirstLine

Default: false

If true, start a multi-line Scaladoc comment body on same line as the opening comment delimiter:

/** This method applies f to each
 *  element of the given list.
 */

If false, start the comment body on a separate line below the opening delimiter:

/**
 * This method applies f to each
 * element of the given list.
 */

newlineAtEndOfFile

Default: false

If true, newlines will be added at the end of all formatted files.

placeScaladocAsterisksBeneathSecondAsterisk

Default: false

If true, Scaladoc asterisks will be placed beneath the second asterisk:

/** Wibble
  * wobble
  */
class A

Otherwise, if false, beneath the first asterisk:

/** Wibble
 *  wobble
 */
class A

preserveSpaceBeforeArguments

Default: false

If true, the formatter will keep an existing space before a parenthesis argument. For example:

stack.pop() should equal (2)

Otherwise, if false, spaces before arguments will always be removed.

danglingCloseParenthesis

Default: Prevent

If Force, any closing parentheses will be set to dangle. For example:

Box(
  contents: List[Thing])

becomes:

Box(
  contents: List[Thing]
)

If Prevent, all dangling parenthesis are collapsed. For example:

Box(
  contents: List[Thing]
)

becomes:

Box(
  contents: List[Thing])

If Preserve, scalariform will try to match what unformatted source code is already doing per parenthesis, either forcing or preventing.

rewriteArrowSymbols

Default: false

Replace arrow tokens with their unicode equivalents: => with , and <- with . For example:

for (n <- 1 to 10) n % 2 match {
  case 0 => println("even")
  case 1 => println("odd")
}

is formatted as:

for (n  1 to 10) n % 2 match {
  case 0  println("even")
  case 1  println("odd")
}

spaceBeforeColon

Default: false

Whether to ensure a space before all single colons. For example, if false, then:

def add[T: Numeric](a: T, b: T): Int = implictly[Numeric[T]].plus(a, b)

If true, then:

def add[T : Numeric](a : T, b : T): Int = implictly[Numeric[T]].plus(a, b)

spaceBeforeContextColon

Default: false

Whether to ensure a space before colons in context bounds (the typeclass pattern). For example, if false, then:

def newArray[T: ClassManifest](n: Int) = new Array[T](n)

If true, then:

def newArray[T : ClassManifest](n: Int) = new Array[T](n)

spaceInsideBrackets

Default: false

Whether to use a space inside type brackets. For example, if true, then:

Array[ String ]

If false, then:

Array[String]

spaceInsideParentheses

Default: false

Whether to use a space inside non-empty parentheses. For example, if true, then:

def main( args : Array[String] )

If false, then:

def main(args : Array[String])

spacesWithinPatternBinders

Default: true

Whether to add a space around the @ token in pattern binders. For example, if true,:

case elem @ Multi(values @ _*) =>

If false,:

case elem@Multi(values@_*) =>

spacesAroundMultiImports

Default: true

Whether or not to add spaces around multi-imports. For example, if false, then:

import a.{b,c,d}
import foo.{bar => baz}

If true, then:

import a.{ b, c, d }
import foo.{ bar => baz }

Compatibility note: Versions 0.1.6 & 0.1.7 of Scalariform used false.

Scala Style Guide

Scalariform is compatible with the Scala Style Guide in the sense that, given the right preference settings, source code that is initially compliant with the Style Guide will not become uncompliant after formatting. In a number of cases, running the formatter will make uncompliant source more compliant.

Preference Value Default?
alignParameters false  
compactStringConcatenation false  
doubleIndentClassDeclaration true No
indentSpaces 2  
placeScaladocAsterisksBeneathSecondAsterisk true No
preserveSpaceBeforeArguments false  
rewriteArrowSymbols false  
spaceBeforeColon false  
spaceInsideBrackets false  
spaceInsideParentheses false  
spacesAroundMultiImports false  

Source Directives

As well as global preferences, formatting can be tweaked at the source level through comments.

format: [ON|OFF]

Disables the formatter for selective portions of a source file:

// format: OFF    <-- this directive disables formatting from this point
class AsciiDSL {
  n ¦- "1" -+ { n: Node =>
          n ¦- "i"
          n ¦- "ii"
          n ¦- "iii"
          n ¦- "iv"
          n ¦- "v"
  }
  n ¦- "2"
  n ¦- "3" -+ { n: Node =>
          n ¦- "i"
          n ¦- "ii" -+ { n: Node =>
                   n ¦- "a"
                   n ¦- "b"
                   n ¦- "c"
          }
          n ¦- "iii"
          n ¦- "iv"
          n ¦- "v"
  }
  // format: ON   <-- formatter resumes from this point
  ...
}
// (see: http://dev.day.com/microsling/content/blogs/main/scalajcr2.html)

format: [+|-]<preferenceName>

Sets a preference for the entirety of the source file, overriding the global formatting settings:

// format: +preserveSpaceBeforeArguments
class StackSpec extends FlatSpec with ShouldMatchers {
  // ...
  stack.pop() should equal (2)
}