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Scalastyle: Implemented Rules

There are 74 rules which are currently implemented:

Checker Description
org.scalastyle.file.FileLengthChecker Check the number of lines in a file.
org.scalastyle.file.FileLineLengthChecker Check the number of characters in a line.
org.scalastyle.file.FileTabChecker Check that there are no tabs in a file.
org.scalastyle.file.HeaderMatchesChecker Check the first lines of each file matches the text.
org.scalastyle.file.IndentationChecker Checks that lines are indented by a multiple of the tab size.
org.scalastyle.file.NewLineAtEofChecker Checks that a file ends with a newline character.
org.scalastyle.file.NoNewLineAtEofChecker Checks that a file does not end with a newline character.
org.scalastyle.file.RegexChecker Checks that a regular expression cannot be matched, if found reports this.
org.scalastyle.file.WhitespaceEndOfLineChecker Check that there is no trailing whitespace at the end of lines.
org.scalastyle.scalariform.BlockImportChecker Checks that block imports are not used.
org.scalastyle.scalariform.CaseBraceChecker Checks that braces aren’t used in case clauses.
org.scalastyle.scalariform.ClassNamesChecker Check that class names match a regular expression.
org.scalastyle.scalariform.ClassTypeParameterChecker Checks that type parameter to a class matches a regular expression.
org.scalastyle.scalariform.CovariantEqualsChecker Check that classes and objects do not define equals without overriding equals(java.lang.Object).
org.scalastyle.scalariform.CurliesImportChecker Checks that curlies imports are not used.
org.scalastyle.scalariform.CyclomaticComplexityChecker Checks that the cyclomatic complexity of a method does exceed a value.
org.scalastyle.scalariform.DeprecatedJavaChecker Checks that Java @Deprecated is not used, Scala @deprecated should be used instead.
org.scalastyle.scalariform.DisallowSpaceAfterTokenChecker Disallow space after certain token(s).
org.scalastyle.scalariform.DisallowSpaceBeforeTokenChecker Disallow space before certain token(s).
org.scalastyle.scalariform.EmptyClassChecker If a class/trait has no members, the braces are unnecessary.
org.scalastyle.scalariform.EmptyInterpolatedStringChecker The interpolation for this string literal is not necessary.
org.scalastyle.scalariform.EnsureSingleSpaceAfterTokenChecker Ensure single space after certain token(s).
org.scalastyle.scalariform.EnsureSingleSpaceBeforeTokenChecker Ensure single space before certain token(s).
org.scalastyle.scalariform.EqualsHashCodeChecker Check that if a class implements either equals or hashCode, it should implement the other.
org.scalastyle.scalariform.FieldNamesChecker Check that field names match a regular expression.
org.scalastyle.scalariform.ForBraceChecker Checks that braces are used in for comprehensions.
org.scalastyle.scalariform.ForLoopChecker Checks that parentheses are used in for loops.
org.scalastyle.scalariform.IfBraceChecker Checks that if statements have braces.
org.scalastyle.scalariform.IllegalImportsChecker Check that a class does not import certain classes.
org.scalastyle.scalariform.ImportGroupingChecker Checks that imports are grouped together, not throughout the file.
org.scalastyle.scalariform.ImportOrderChecker Checks that imports are grouped and ordered according to the style configuration.
org.scalastyle.scalariform.LowercasePatternMatchChecker Checks that a case statement pattern match is not lower case, as this can cause confusion.
org.scalastyle.scalariform.MagicNumberChecker Checks for use of magic numbers.
org.scalastyle.scalariform.MethodArgumentNamesChecker Check that method argument names match a regular expression.
org.scalastyle.scalariform.MethodLengthChecker Checks that methods do not exceed a maximum length.
org.scalastyle.scalariform.MethodNamesChecker Check that method names match a regular expression.
org.scalastyle.scalariform.MultipleStringLiteralsChecker Checks that a string literal does not appear multiple times.
org.scalastyle.scalariform.NamedArgumentChecker Checks that argument literals are named.
org.scalastyle.scalariform.NoCloneChecker Check that classes and objects do not define the clone() method.
org.scalastyle.scalariform.NoFinalizeChecker Check that classes and objects do not define the finalize() method.
org.scalastyle.scalariform.NoWhitespaceAfterLeftBracketChecker No whitespace after left bracket ‘[’.
org.scalastyle.scalariform.NoWhitespaceBeforeLeftBracketChecker No whitespace before left bracket ‘[’.
org.scalastyle.scalariform.NoWhitespaceBeforeRightBracketChecker No whitespace before right bracket ‘’]’’.
org.scalastyle.scalariform.NonASCIICharacterChecker Some editors are unfriendly to non ASCII characters.
org.scalastyle.scalariform.NotImplementedErrorUsage Checks that the code does not have ??? operators.
org.scalastyle.scalariform.NullChecker Check that null is not used.
org.scalastyle.scalariform.NumberOfMethodsInTypeChecker Check that a class / trait / object does not have too many methods.
org.scalastyle.scalariform.NumberOfTypesChecker Checks that there are not too many types declared in a file.
org.scalastyle.scalariform.ObjectNamesChecker Check that object names match a regular expression.
org.scalastyle.scalariform.OverrideJavaChecker Checks that Java @Override is not used.
org.scalastyle.scalariform.PackageNamesChecker Check that package names match a regular expression.
org.scalastyle.scalariform.PackageObjectNamesChecker Check that package object names match a regular expression.
org.scalastyle.scalariform.ParameterNumberChecker Maximum number of parameters for a method.
org.scalastyle.scalariform.PatternMatchAlignChecker Check that pattern match arrows align.
org.scalastyle.scalariform.ProcedureDeclarationChecker Use a : Unit = for procedure declarations.
org.scalastyle.scalariform.PublicMethodsHaveTypeChecker Check that a method has an explicit return type, it is not inferred.
org.scalastyle.scalariform.RedundantIfChecker Checks that if expressions are not redundant, i.e. easily replaced by a variant of the condition.
org.scalastyle.scalariform.ReturnChecker Check that return is not used.
org.scalastyle.scalariform.ScalaDocChecker Checks that the ScalaDoc on documentable members is well-formed.
org.scalastyle.scalariform.SimplifyBooleanExpressionChecker Boolean expression can be simplified.
org.scalastyle.scalariform.SpaceAfterCommentStartChecker Checks a space after the start of the comment.
org.scalastyle.scalariform.SpacesAfterPlusChecker Check that the plus sign is followed by a space.
org.scalastyle.scalariform.SpacesBeforePlusChecker Check that the plus sign is preceded by a space.
org.scalastyle.scalariform.StructuralTypeChecker Check that structural types are not used.
org.scalastyle.scalariform.ThrowChecker Checks that throw is not used.
org.scalastyle.scalariform.TodoCommentChecker Check for use of TODO/FIXME single line comments.
org.scalastyle.scalariform.TokenChecker Checks that a regular expression cannot be matched in a token, if found reports this.
org.scalastyle.scalariform.UnderscoreImportChecker Avoid wildcard imports.
org.scalastyle.scalariform.UppercaseLChecker Checks that if a long literal is used, then an uppercase L is used.
org.scalastyle.scalariform.VarFieldChecker Checks that classes and objects do not define mutable fields.
org.scalastyle.scalariform.VarLocalChecker Checks that functions do not define mutable variables.
org.scalastyle.scalariform.WhileBraceChecker Checks that while body have braces.
org.scalastyle.scalariform.WhileChecker Checks that while is not used.
org.scalastyle.scalariform.XmlLiteralChecker Check that XML literals are not used.

org.scalastyle.file.FileLengthChecker - Check the number of lines in a file.

Justification

Files which are too long can be hard to read and understand.

Parameters

ParameterDescriptionTypeDefault Value
maxFileLength Maximum file length integer 1500

Example configuration

<check enabled="true" class="org.scalastyle.file.FileLengthChecker" level="warning">
 <parameters>
  <parameter name="maxFileLength">800</parameter>
 </parameters>
</check>

org.scalastyle.file.FileLineLengthChecker - Check the number of characters in a line.

Justification

Lines that are too long can be hard to read and horizontal scrolling is annoying.

Parameters

ParameterDescriptionTypeDefault Value
maxLineLength Maximum line length integer 160
tabSize Tab size integer 4
ignoreImports Ignore import statements boolean false

Example configuration

<check enabled="true" class="org.scalastyle.file.FileLineLengthChecker" level="warning">
 <parameters>
  <parameter name="maxLineLength">100</parameter>
  <parameter name="tabSize">2</parameter>
  <parameter name="ignoreImports">true</parameter>
 </parameters>
</check>

org.scalastyle.file.FileTabChecker - Check that there are no tabs in a file.

Justification

Some say that tabs are evil.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.file.FileTabChecker" level="warning"/>

org.scalastyle.file.HeaderMatchesChecker - Check the first lines of each file matches the text.

Justification

A lot of projects require a header with a copyright notice, or they require a license in each file. This does a simple text comparison between the header and the first lines of the file. You can have multiple lines, but make sure you surround the text with a CDATA section. You can also specify a regular expression, as long as you set the regex parameter to true.

Parameters

ParameterDescriptionTypeDefault Value
header Header string
regex Header Regex boolean false

Example configuration

<check enabled="true" class="org.scalastyle.file.HeaderMatchesChecker" level="warning">
 <parameters>
  <parameter name="regex">false</parameter>
  <parameter name="header">// Copyright \(C\) 2011-2012 the original author or authors.</parameter>
 </parameters>
</check>

or

<check enabled="true" class="org.scalastyle.file.HeaderMatchesChecker" level="warning">
 <parameters>
  <parameter name="regex">true</parameter>
  <parameter name="header">// Copyright \(C\) (?:\d{4}-)?\d{4} the original author or authors.</parameter>
 </parameters>
</check>

org.scalastyle.file.IndentationChecker - Checks that lines are indented by a multiple of the tab size.

Justification

Code that is not indented consistently can be hard to read.

Parameters

ParameterDescriptionTypeDefault Value
tabSize Tab size integer 2
methodParamIndentSize Multi-line method parameter spacing integer 2
classParamIndentSize Multi-line class parameter spacing integer 4

Example configuration

<check enabled="true" class="org.scalastyle.file.IndentationChecker" level="warning">
 <parameters>
  <parameter name="tabSize">2</parameter>
  <parameter name="methodParamIndentSize">2</parameter>
  <parameter name="classParamIndentSize">4</parameter>
 </parameters>
</check>

org.scalastyle.file.NewLineAtEofChecker - Checks that a file ends with a newline character.

Justification

Some version control systems don’t cope well with files which don’t end with a newline character.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.file.NewLineAtEofChecker" level="warning"/>

org.scalastyle.file.NoNewLineAtEofChecker - Checks that a file does not end with a newline character.

Justification

Because Mirco Dotta wanted it.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.file.NoNewLineAtEofChecker" level="warning"/>

org.scalastyle.file.RegexChecker - Checks that a regular expression cannot be matched, if found reports this.

Justification

Some checks can be carried out with a regular expression.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string
line Line boolean false

Example configuration

<check enabled="true" class="org.scalastyle.file.RegexChecker" level="warning">
 <parameters>
  <parameter name="regex">(?m)^\s*$(\r|)\n^\s*$(\r|)\n</parameter>
  <parameter name="line">false</parameter>
 </parameters>
 <customMessage>No double blank lines</customMessage>
</check>

org.scalastyle.file.WhitespaceEndOfLineChecker - Check that there is no trailing whitespace at the end of lines.

Justification

Whitespace at the end of a line can cause problems when diffing between files or between versions.

Parameters

ParameterDescriptionTypeDefault Value
ignoreWhitespaceLines Ignore lines with just whitespace boolean false

Example configuration

<check enabled="true" class="org.scalastyle.file.WhitespaceEndOfLineChecker" level="warning">
 <parameters>
  <parameter default="false" type="boolean" name="ignoreWhitespaceLines"/>
 </parameters>
</check>

org.scalastyle.scalariform.BlockImportChecker - Checks that block imports are not used.

Justification

Block imports, e.g. import a.{b, c} can lead to annoying merge errors in large code bases that are maintained by lot of developers. This rule allows to ensure that only single imports are used in order to minimize merge errors in import declarations.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.BlockImportChecker" level="warning"/>

org.scalastyle.scalariform.CaseBraceChecker - Checks that braces aren’t used in case clauses.

Justification

Braces aren’t required in case clauses. They should be omitted according to Scala Style Guide.

Parameters

No parameters

Example configuration

<check enabled="true" level="warning" class="org.scalastyle.scalariform.CaseBraceChecker"/>

org.scalastyle.scalariform.ClassNamesChecker - Check that class names match a regular expression.

Justification

The Scala style guide recommends that class names conform to certain standards.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[A-Z][A-Za-z]*$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ClassNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[A-Z][A-Za-z]*$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.ClassTypeParameterChecker - Checks that type parameter to a class matches a regular expression.

Justification

Scala generic type names are generally single upper case letters. This check checks for classes and traits. Note that this check only checks the innermost type parameter, to allow for List[T].

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[A-Z_]$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ClassTypeParameterChecker" level="warning">
 <parameters>
  <parameter name="regex">^[A-Z_]$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.CovariantEqualsChecker - Check that classes and objects do not define equals without overriding equals(java.lang.Object).

Justification

Mistakenly defining a covariant equals() method without overriding method equals(java.lang.Object) can produce unexpected runtime behaviour.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.CovariantEqualsChecker" level="warning"/>

org.scalastyle.scalariform.CurliesImportChecker - Checks that curlies imports are not used.

Justification

Curlies imports, e.g. import a.{b, c}, can lead to annoying merge errors in large code bases that are maintained by lot of developers. This rule allows to ensure that only single imports, no renaming and no hiding imports are used in order to minimize merge errors in import declarations.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.CurliesImportChecker" level="warning"/>

org.scalastyle.scalariform.CyclomaticComplexityChecker - Checks that the cyclomatic complexity of a method does exceed a value.

Justification

If the code is too complex, then this can make code hard to read.

Parameters

ParameterDescriptionTypeDefault Value
maximum Maximum integer 10
countCases Count Cases boolean true

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.CyclomaticComplexityChecker" level="warning">
 <parameters>
  <parameter name="maximum">10</parameter>
  <parameter name="countCases">true</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.DeprecatedJavaChecker - Checks that Java @Deprecated is not used, Scala @deprecated should be used instead.

Justification

You should be using the Scala @deprecated instead.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.DeprecatedJavaChecker" level="warning"/>

org.scalastyle.scalariform.DisallowSpaceAfterTokenChecker - Disallow space after certain token(s).

Justification

Correct formatting can help readability.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.DisallowSpaceAfterTokenChecker" level="warning">
 <parameters>
  <parameter name="tokens">LPAREN</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.DisallowSpaceBeforeTokenChecker - Disallow space before certain token(s).

Justification

Correct formatting can help readability.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.DisallowSpaceBeforeTokenChecker" level="warning">
 <parameters>
  <parameter name="tokens">COLON, COMMA, RPAREN</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.EmptyClassChecker - If a class/trait has no members, the braces are unnecessary.

Justification

If a class / trait has no members, then braces are unnecessary, and can be removed.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.EmptyClassChecker" level="warning"/>

org.scalastyle.scalariform.EmptyInterpolatedStringChecker - The interpolation for this string literal is not necessary.

Justification

Empty interpolated strings are harder to read and not necessary.

Parameters

No parameters

Example configuration

<check enabled="true" level="warning" class="org.scalastyle.scalariform.EmptyInterpolatedStringChecker"/>

org.scalastyle.scalariform.EnsureSingleSpaceAfterTokenChecker - Ensure single space after certain token(s).

Justification

Correct formatting can help readability.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.EnsureSingleSpaceAfterTokenChecker" level="warning">
 <parameters>
  <parameter name="tokens">COLON, IF</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.EnsureSingleSpaceBeforeTokenChecker - Ensure single space before certain token(s).

Justification

Correct formatting can help readability.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.EnsureSingleSpaceBeforeTokenChecker" level="warning">
 <parameters>
  <parameter name="tokens">LPAREN</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.EqualsHashCodeChecker - Check that if a class implements either equals or hashCode, it should implement the other.

Justification

Defining either equals or hashCode in a class without defining the is a known source of bugs. Usually, when you define one, you should also define the other.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.EqualsHashCodeChecker" level="warning"/>

org.scalastyle.scalariform.FieldNamesChecker - Check that field names match a regular expression.

Justification

A consistent naming convention for field names can make code easier to read and understand.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[a-z][A-Za-z0-9]*$
objectFieldRegex Regular expression for constants string ^[A-Z][A-Za-z0-9]*$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.FieldNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[a-z][A-Za-z0-9]*$</parameter>
  <parameter name="objectFieldRegex">^[A-Z][A-Za-z0-9]*$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.ForBraceChecker - Checks that braces are used in for comprehensions.

Justification

Usage of braces (rather than parentheses) within a for comprehension mean that you don’t have to specify a semi-colon at the end of every line:

for { // braces
  t <- List(1,2,3)
  if (t % 2 == 0)
} yield t

is preferred to

for ( // parentheses
  t <- List(1,2,3);
  if (t % 2 == 0)
) yield t

To fix it, replace the () with {}. And then remove the ; at the end of the lines.

Description

The singleLineAllowed property allows for constructions of the type:

for (i <- List(1,2,3)) yield i

Parameters

ParameterDescriptionTypeDefault Value
singleLineAllowed Allow parentheses for single-line for boolean false

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ForBraceChecker" level="warning">
 <parameters>
  <parameter name="singleLineAllowed">true</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.ForLoopChecker - Checks that parentheses are used in for loops.

Justification

For-comprehensions which lack a yield clause is actually a loop rather than a functional comprehension and it is usually more readable to string the generators together between parentheses rather than using the syntactically-confusing } { construct:

for (x <- board.rows; y <- board.files) {
  printf("(%d, %d)", x, y)
}

is preferred to

for {
  x <- board.rows
  y <- board.files
} {
  printf("(%d, %d)", x, y)
}

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ForLoopChecker" level="warning"/>

org.scalastyle.scalariform.IfBraceChecker - Checks that if statements have braces.

Justification

Some people find if clauses with braces easier to read.

Description

The singleLineAllowed property allows if constructions of the type:

if (bool_expression) expression1 else expression2

The doubleLineAllowed property allows if constructions of the type:

if (bool_expression) expression1 else expression2

Note: If you intend to enable only if expressions in the format below, disable the IfBraceChecker altogether.

if (bool_expression) expression1 else expression2

Parameters

ParameterDescriptionTypeDefault Value
singleLineAllowed Single Line Allowed boolean true
doubleLineAllowed Double Line Allowed boolean false

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.IfBraceChecker" level="warning">
 <parameters>
  <parameter name="singleLineAllowed">true</parameter>
  <parameter name="doubleLineAllowed">false</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.IllegalImportsChecker - Check that a class does not import certain classes.

Justification

Use of some classes can be discouraged for a project. For instance, use of sun._ is generally discouraged because they are internal to the JDK and can be changed.

Parameters

ParameterDescriptionTypeDefault Value
illegalImports Illegal Imports string sun._,java.awt._

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.IllegalImportsChecker" level="warning"/>

org.scalastyle.scalariform.ImportGroupingChecker - Checks that imports are grouped together, not throughout the file.

Justification

If imports are spread throughout the file, knowing what is in scope at any one place can be difficult to work out.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ImportGroupingChecker" level="warning"/>

org.scalastyle.scalariform.ImportOrderChecker - Checks that imports are grouped and ordered according to the style configuration.

Justification

Consistent import ordering improves code readability and reduces unrelated changes in patches.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ImportOrderChecker" level="warning">
 <parameters>
  <parameter name="groups">java,scala,others</parameter>
  <parameter name="group.java">javax?\..+</parameter>
  <parameter name="group.scala">scala\..+</parameter>
  <parameter name="group.others">.+</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.LowercasePatternMatchChecker - Checks that a case statement pattern match is not lower case, as this can cause confusion.

Justification

A lower case pattern match clause with no other tokens is the same as _; this is not true for patterns which start with an upper case letter. This can cause confusion, and may not be what was intended:

val foo = "foo"
val Bar = "bar"
"bar" match { case Bar => "we got bar" } // result = "we got bar"
"bar" match { case foo => "we got foo" } // result = "we got foo"
"bar" match { case `foo` => "we got foo" } // result = MatchError

This checker raises a warning with the second match. To fix it, use an identifier which starts with an upper case letter (best), use case _ or, if you wish to refer to the value, add a type : Any, e.g.:

val lc = "lc"
"something" match { case lc: Any => "lc" } // result = "lc"
"something" match { case _ => "lc" } // result = "lc"

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.LowercasePatternMatchChecker" level="warning"/>

org.scalastyle.scalariform.MagicNumberChecker - Checks for use of magic numbers.

Justification

Replacing a magic number with a named constant can make code easier to read and understand, and can avoid some subtle bugs.

Description

A simple assignment to a val is not considered to be a magic number, for example: val foo = 4 is not a magic number, but var foo = 4 is considered to be a magic number.

Parameters

ParameterDescriptionTypeDefault Value
ignore Ignore string -1,0,1,2

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.MagicNumberChecker" level="warning">
 <parameters>
  <parameter name="ignore">-1,0,1,2,3</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.MethodArgumentNamesChecker - Check that method argument names match a regular expression.

Justification

The Scala style guide recommends that method argument names conform to certain standards.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[a-z][A-Za-z0-9]*$
ignoreRegex Regular expression to ignore string ^$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.MethodArgumentNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[a-z][A-Za-z0-9]*$</parameter>
  <parameter name="ignoreRegex">^$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.MethodLengthChecker - Checks that methods do not exceed a maximum length.

Justification

Long methods can be hard to read and understand.

Parameters

ParameterDescriptionTypeDefault Value
maxLength Maximum length integer 50
ignoreComments Ignore comments boolean false
ignoreEmpty Ignore empty lines boolean false

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.MethodLengthChecker" level="warning">
 <parameters>
  <parameter name="maxLength">50</parameter>
  <parameter name="ignoreComments">false</parameter>
  <parameter name="ignoreEmpty">false</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.MethodNamesChecker - Check that method names match a regular expression.

Justification

The Scala style guide recommends that method names conform to certain standards. If the methods are overriding another method, and the overridden method cannot be changed, then use the ignoreOverride parameter.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[a-z][A-Za-z0-9]*(_=)?$
ignoreRegex Regular expression to ignore string ^$
ignoreOverride Ignore override boolean false

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.MethodNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[A-Za-z]*$</parameter>
  <parameter name="ignoreRegex">^.*$</parameter>
  <parameter name="ignoreOverride">false</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.MultipleStringLiteralsChecker - Checks that a string literal does not appear multiple times.

Justification

Code duplication makes maintenance more difficult, so it can be better to replace the multiple occurrences with a constant.

Parameters

ParameterDescriptionTypeDefault Value
allowed Maximum occurences allowed integer 1
ignoreRegex Ignore regular expression string ^""$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.MultipleStringLiteralsChecker" level="warning">
 <parameters>
  <parameter name="allowed">1</parameter>
  <parameter name="ignoreRegex">^\&quot;\&quot;$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.NamedArgumentChecker - Checks that argument literals are named.

Justification

Nameless literals make code harder to understand (consider updateEntity(1, true) and updateEntity(id = 1, enabled = true)).

Parameters

ParameterDescriptionTypeDefault Value
checkString Check string literals boolean false
ignoreMethod Ignore methods by pattern string ^set.+$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NamedArgumentChecker" level="warning">
 <parameters>
  <parameter name="checkString">false</parameter>
  <parameter name="ignoreMethod">^set.+$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.NoCloneChecker - Check that classes and objects do not define the clone() method.

Justification

The clone method is difficult to get right. You can use the copy constructor of case classes rather than implementing clone. For more information on clone(), see Effective Java by Joshua Bloch pages.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NoCloneChecker" level="warning"/>

org.scalastyle.scalariform.NoFinalizeChecker - Check that classes and objects do not define the finalize() method.

Justification

finalize() is called when the object is garbage collected, and garbage collection is not guaranteed to happen. It is therefore unwise to rely on code in finalize() method.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NoFinalizeChecker" level="warning"/>

org.scalastyle.scalariform.NoWhitespaceAfterLeftBracketChecker - No whitespace after left bracket ‘[’.

Justification

If there is whitespace after a left bracket, this can be confusing to the reader.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NoWhitespaceAfterLeftBracketChecker" level="warning"/>

org.scalastyle.scalariform.NoWhitespaceBeforeLeftBracketChecker - No whitespace before left bracket ‘[’.

Justification

If there is whitespace before a left bracket, this can be confusing to the reader.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NoWhitespaceBeforeLeftBracketChecker" level="warning"/>

org.scalastyle.scalariform.NoWhitespaceBeforeRightBracketChecker - No whitespace before right bracket ‘’]’’.

Justification

If there is whitespace before a right bracket, this can be confusing to the reader.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NoWhitespaceBeforeRightBracketChecker" level="warning"/>

org.scalastyle.scalariform.NonASCIICharacterChecker - Some editors are unfriendly to non ASCII characters.

Justification

Scala allows unicode characters as operators and some editors misbehave when they see non-ascii character. In a project collaborated by a community of developers. This check can be helpful in such situations.

"value" match {
  case "value" => println("matched")
  ...
}

is preferred to

"value" match {
  case "value"  println("matched")
  ...
}

To fix it, replace the (unicode operator) with =>.

Parameters

ParameterDescriptionTypeDefault Value
allowStringLiterals Allow non-ASCII scripts in string literals. boolean false

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NonASCIICharacterChecker" level="warning">
 <parameters>
  <parameter name="allowStringLiterals">true</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.NotImplementedErrorUsage - Checks that the code does not have ??? operators.

Justification

The ??? operator denotes that an implementation is missing. This rule helps to avoid potential runtime errors because of not implemented code.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NotImplementedErrorUsage" level="warning"/>

org.scalastyle.scalariform.NullChecker - Check that null is not used.

Justification

Scala discourages use of null, preferring Option.

Parameters

ParameterDescriptionTypeDefault Value
allowNullChecks Allow null checks boolean true

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NullChecker" level="warning">
 <parameters>
  <parameter name="allowNullChecks">true</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.NumberOfMethodsInTypeChecker - Check that a class / trait / object does not have too many methods.

Justification

If a type declares too many methods, this can be an indication of bad design.

Parameters

ParameterDescriptionTypeDefault Value
maxMethods Maximum methods integer 30

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NumberOfMethodsInTypeChecker" level="warning">
 <parameters>
  <parameter name="maxMethods">30</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.NumberOfTypesChecker - Checks that there are not too many types declared in a file.

Justification

If there are too many classes/objects defined in a single file, this can cause the code to be difficult to understand.

Parameters

ParameterDescriptionTypeDefault Value
maxTypes Maximum Number integer 20

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.NumberOfTypesChecker" level="warning">
 <parameters>
  <parameter name="maxTypes">20</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.ObjectNamesChecker - Check that object names match a regular expression.

Justification

The Scala style guide recommends that object names conform to certain standards.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[A-Z][A-Za-z]*$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ObjectNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[A-Z][A-Za-z]*$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.OverrideJavaChecker - Checks that Java @Override is not used.

Justification

You should be using the Scala override keyword instead.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.OverrideJavaChecker" level="warning"/>

org.scalastyle.scalariform.PackageNamesChecker - Check that package names match a regular expression.

Justification

The Scala style guide recommends that package names conform to certain standards.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[a-z]+$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.PackageNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[a-z]+$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.PackageObjectNamesChecker - Check that package object names match a regular expression.

Justification

The Scala style guide recommends that package object names conform to certain standards.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^[a-z][A-Za-z]*$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.PackageObjectNamesChecker" level="warning">
 <parameters>
  <parameter name="regex">^[a-z][A-Za-z]*$</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.ParameterNumberChecker - Maximum number of parameters for a method.

Justification

A method which has more than a certain number of parameters can be hard to understand.

Parameters

ParameterDescriptionTypeDefault Value
maxParameters Maximum Number integer 8

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ParameterNumberChecker" level="warning">
 <parameters>
  <parameter name="maxParameters">8</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.PatternMatchAlignChecker - Check that pattern match arrows align.

Justification

Correct formatting can help readability.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.PatternMatchAlignChecker" level="warning"/>

org.scalastyle.scalariform.ProcedureDeclarationChecker - Use a : Unit = for procedure declarations.

Justification

A procedure style declaration can cause confusion - the developer may have simply forgotten to add a =, and now their method returns Unit rather than the inferred type:

def foo() { println("hello"); 5 }

This checker raises a warning with the first line. To fix it, use an explicit return type, or add a = before the body.

def foo() = { println("hello"); 5 }

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ProcedureDeclarationChecker" level="warning"/>

org.scalastyle.scalariform.PublicMethodsHaveTypeChecker - Check that a method has an explicit return type, it is not inferred.

Justification

A public method declared on a type is effectively an API declaration. Explicitly declaring a return type means that other code which depends on that type won’t break unexpectedly.

Parameters

ParameterDescriptionTypeDefault Value
ignoreOverride Ignore overridden methods boolean false

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.PublicMethodsHaveTypeChecker" level="warning">
 <parameters>
  <parameter name="ignoreOverride">false</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.RedundantIfChecker - Checks that if expressions are not redundant, i.e. easily replaced by a variant of the condition.

Justification

If expressions with boolean constants in both branches can be eliminated without affecting readability. Prefer simply cond to if (cond) true else false and !cond to if (cond) false else true.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.RedundantIfChecker" level="warning"/>

org.scalastyle.scalariform.ReturnChecker - Check that return is not used.

Justification

Use of return is not usually necessary in Scala. In fact, use of return can discourage a functional style of programming.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ReturnChecker" level="warning"/>

org.scalastyle.scalariform.ScalaDocChecker - Checks that the ScalaDoc on documentable members is well-formed.

Justification

Scaladoc is generally considered a good thing. Within reason.

Description

Ignore tokens is a comma separated string that may include the following: PatDefOrDcl (variables), TmplDef (classes, traits), TypeDefOrDcl (type definitions), FunDefOrDcl (functions). Supported indentation styles are “scaladoc” (for ScalaDoc-style comments, with two spaces before the asterisk), “javadoc” (for JavaDoc-style comments, with a single space before the asterisk) or “anydoc” to support any style (any number of spaces before the asterisk). For backwards compatibility, if left empty, “anydoc” will be assumed.

Parameters

ParameterDescriptionTypeDefault Value
ignoreRegex Regular expression string ^$
ignoreTokenTypes Comma Separated String string ^$
ignoreOverride Ignore override boolean false
indentStyle Force indent style string anydoc

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ScalaDocChecker" level="warning">
 <parameters>
  <parameter name="ignoreRegex">(.*Spec$)|(.*SpecIT$)</parameter>
  <parameter name="ignoreTokenTypes">PatDefOrDcl,TypeDefOrDcl,FunDefOrDcl,TmplDef</parameter>
  <parameter name="ignoreOverride">false</parameter>
  <parameter name="indentStyle">anydoc</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.SimplifyBooleanExpressionChecker - Boolean expression can be simplified.

Justification

A boolean expression which can be simplified can make code easier to read.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.SimplifyBooleanExpressionChecker" level="warning"/>

org.scalastyle.scalariform.SpaceAfterCommentStartChecker - Checks a space after the start of the comment.

Justification

To bring consistency with how comments should be formatted, leave a space right after the beginning of the comment.

package foobar

object Foobar {
  /**WRONG
    *
    */
  /** Correct
    *
    */
  val d = 2 /*Wrong*/ //Wrong
  /**
    * Correct
    */
  val e = 3 /** Correct*/ // Correct
}

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.SpaceAfterCommentStartChecker" level="warning"/>

org.scalastyle.scalariform.SpacesAfterPlusChecker - Check that the plus sign is followed by a space.

Justification

An expression with spaces around + can be easier to read.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.SpacesAfterPlusChecker" level="warning"/>

org.scalastyle.scalariform.SpacesBeforePlusChecker - Check that the plus sign is preceded by a space.

Justification

An expression with spaces around + can be easier to read.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.SpacesBeforePlusChecker" level="warning"/>

org.scalastyle.scalariform.StructuralTypeChecker - Check that structural types are not used.

Justification

Structural types in Scala can use reflection - this can have unexpected performance consequences. Warning: This check can also wrongly pick up type lamdbas and other such constructs. This checker should be used with care. You always have the alternative of the scalac checking for structural types.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.StructuralTypeChecker" level="warning"/>

org.scalastyle.scalariform.ThrowChecker - Checks that throw is not used.

Justification

throw statements should be replaced with type-safe error constructs like Try and Either, which communicate the possibility of error in the type signature.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.ThrowChecker" level="warning"/>

org.scalastyle.scalariform.TodoCommentChecker - Check for use of TODO/FIXME single line comments.

Justification

Some projects may consider TODO or FIXME comments in a code bad style. They would rather you fix the problem.

Parameters

ParameterDescriptionTypeDefault Value
words Word list string TODO|FIXME

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.TodoCommentChecker" level="warning">
 <parameters>
  <parameter default="TODO|FIXME" type="string" name="words"/>
 </parameters>
</check>

org.scalastyle.scalariform.TokenChecker - Checks that a regular expression cannot be matched in a token, if found reports this.

Justification

Some checks can be carried by just the presence of a particular token.

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string ^$

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.TokenChecker" level="warning">
 <parameters>
  <parameter name="regex">^[ai]sInstanceOf$</parameter>
 </parameters>
 <customMessage>Avoid casting.</customMessage>
</check>

org.scalastyle.scalariform.UnderscoreImportChecker - Avoid wildcard imports.

Justification

Importing all classes from a package or static members from a class leads to tight coupling between packages or classes and might lead to problems when a new version of a library introduces name clashes.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.UnderscoreImportChecker" level="warning">
 <parameters>
  <parameter name="ignoreRegex">collection\.JavaConverters\._|scala\.concurrent\.duration\._</parameter>
 </parameters>
</check>

org.scalastyle.scalariform.UppercaseLChecker - Checks that if a long literal is used, then an uppercase L is used.

Justification

A lowercase L (l) can look similar to a number 1 with some fonts.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.UppercaseLChecker" level="warning"/>

org.scalastyle.scalariform.VarFieldChecker - Checks that classes and objects do not define mutable fields.

Justification

var (mutable fields) are deprecated if you’re using a strict functional style.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.VarFieldChecker" level="warning"/>

org.scalastyle.scalariform.VarLocalChecker - Checks that functions do not define mutable variables.

Justification

var (mutable local variables) are deprecated if you’re using a strict functional style.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.VarLocalChecker" level="warning"/>

org.scalastyle.scalariform.WhileBraceChecker - Checks that while body have braces.

Justification

While cannot be used in a pure-functional manner, that’s why it’s recommended to never omit braces according to Scala Style Guide.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.WhileBraceChecker" level="warning"/>

org.scalastyle.scalariform.WhileChecker - Checks that while is not used.

Justification

while loops are deprecated if you’re using a strict functional style.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.WhileChecker" level="warning"/>

org.scalastyle.scalariform.XmlLiteralChecker - Check that XML literals are not used.

Justification

Some projects prefer not to have XML literals. They could use a templating engine instead.

Parameters

No parameters

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.XmlLiteralChecker" level="warning"/>