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Scalariform

Scalariform is a code formatter for Scala 2.8+. It is a library and a stand-alone command line tool, with integrations available for Eclipse, Emacs (via ENSIME), jEdit, Maven, sbt and TextMate. Currently, Scalariform supports only a limited set of options, although it is intended to be compatible with the recommendations of the Scala Style Guide (see below). Please let me know what other features people would like.

Scalariform is licenced under The MIT Licence.

Download

Scalariform is available from Scala-tools.org:

http://scala-tools.org/repo-releases/org/scalariform/scalariform_2.8.0/0.0.8/

If you're using sbt, you can declare a dependency as follows:

val scalariform = "org.scalariform" %% "scalariform" % "0.0.8"

Integration with Eclipse

Scala IDE for Eclipse uses Scalariform for formatting:

http://download.scala-ide.org/

(See http://www.assembla.com/wiki/show/scala-ide/Requirements_and_Installation for more detailed instructions.)

Formatting works the same in the Scala editor; that is, either

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

To configure preferences, go to Window -> Preferences -> Scala -> Formatter

It can also perform formatting as a save action (Window -> Preferences -> Java -> Editor -> Save Actions).

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. It is not yet on scala-tools, but you can build it from the source.

Usage:

<plugin>
  <groupId>org.scalariform</groupId>
  <artifactId>scalariform-maven-plugin</artifactId>
  <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.

Integration with TextMate

See Mads Jensen's Scala TextMate bundle:

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

Reformat using Ctrl-Shift-H.

Command line tool

Scalariform includes a stand-alone command line utility. Sample script:

#!/bin/bash
scala -cp /path/to/scalariform-0.0.8.jar scalariform.commandline.Main "$@"

Usage:

Usage: scalariform [options] [files...]

Options:
  --encoding=<encoding>           Set the encoding, e.g. UTF-8. If not set, defaults to the platform default encoding.
  --fileList=<path>, -l=<path>    Read the list of input file(s) from a text file (one per line)
  --help, -h                      Show help
  --inPlace, -i                   Replace the input file(s) in place with a formatted version.
  --test, -t                      Check the input(s) to see if they are correctly formatted, return a non-zero error code if not.
  --verbose, -v                   Verbose output
  --version                       Show Scalariform version

Preferences:
  [+|-]alignParameters                                  Enable/disable Align parameters on different lines in the same column
  [+|-]alignSingleLineCaseStatements                    Enable/disable Align the arrows of consecutive single-line case statements
  [+|-]compactStringConcatenation                       Enable/disable Omit spaces when formatting a '+' operator on String literals
  [+|-]doubleIndentClassDeclaration                     Enable/disable Double indent either a class's parameters or its inheritance list
  [+|-]formatXml                                        Enable/disable Format XML literals
  [+|-]indentLocalDefs                                  Enable/disable Indent local defs an extra level
  [+|-]indentPackageBlocks                              Enable/disable Indent package blocks
  [+|-]preserveSpaceBeforeArguments                     Enable/disable Preserve a space before a parenthesis argument
  [+|-]rewriteArrowSymbols                              Enable/disable Replace arrow tokens with unicode equivalents: => with ⇒, and <- with ←
  [+|-]spaceBeforeColon                                 Enable/disable Add a space before colons
  -alignSingleLineCaseStatements.maxArrowIndent=[1-100] Set Maximum number of spaces inserted before an arrow to align case statements
  -indentSpaces=[1-10]                                  Set Number of spaces to use for indentation

Examples:
 scalariform +spaceBeforeColon -alignParameters -indentSpaces=2 --inPlace foo.scala
 find . -name '*.scala' | xargs scalariform +rewriteArrowSymbols --verbose --test
 echo 'class A ( n  :Int )' | scalariform

Library

Example usage:

import scalariform.formatter.preferences._
import scalariform.formatter.ScalaFormatter
import scalariform.parser.ScalaParserException

object Test extends Application {

  val unformattedScala = """
    class A  {
    println (42)}"""
  val preferences = FormattingPreferences().setPreference(IndentSpaces, 3)
  try {
    val formattedScala = ScalaFormatter.format(unformattedScala, preferences)
    println(formattedScala)
  } catch {
     case e: ScalaParserException => println("Syntax error in Scala source")
  }

}

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)

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
}

alignSingleLineCaseStatements.maxArrowIndent

Default: 40

When using alignSingleLineCaseStatements == 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
}

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.

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

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.

Preference Value Default?
alignParameters false  
compactStringConcatenation false  
doubleIndentClassDeclaration true No
indentSpaces 2  
preserveSpaceBeforeArguments false  
rewriteArrowSymbols false  
spaceBeforeColon 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 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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