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Scala source code formatter

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.

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 Window -> Preferences -> 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."

http://aemon.com/file_dump/ensime_manual.html#tth_sEc4.8

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 sbt

sbt-scalariform, written by Olivier Michallat, provides an sbt plugin contributing formatting actions for sbt 0.7.x.

A version for sbt 0.10.x has been written by Peter Vlugter: https://github.com/typesafehub/sbt-scalariform

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 gq command by adding the following to .vimrc

au BufEnter *.scala setl formatprg=/path/to/scalariform.jar\ --stdin\ --stdout

The executable scalariform.jar can be downloaded from:

https://s3.amazonaws.com/scalariform/scalariform.jar

Command line tool

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

Library

https://github.com/mdr/scalariform/wiki/Library

Preferences

alignParameters

Default: false

Align class/function parameters in the same column. For example, if false, then:

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

If true, then:

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

This option is disabled if indentWithTabs is true.

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, 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 = ...
}

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 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.
 */

preserveDanglingCloseParenthesis

Default: false

If true, it will keep a newline before a close parenthesis ')' in an argument expression. For example:

val book = Book(
  name = "Name",
  author = "Author",
  rating = 5
)

If false, the parenthesis will be joined to the end of the argument list:

val book = Book(
  name = "Name",
  author = "Author",
  rating = 5)

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.

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 colon. For example, If false, then:

def add(a: Int, b: Int): Int = a + b

If true, then:

def add(a : Int, b : Int) : Int = a + b

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@_*) =>

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 compiliant with the Style Guide will not become uncompliant after formatting. In a number of cases, running the formatter will make uncompliant source more compliant.

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 entire of the source file, overriding the global formatting settings:

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