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Scalastyle: Implemented Rules

There are 56 rules which are currently implemented:

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 default="100" type="integer" name="maxLineLength"/>
  <parameter default="2" type="integer" name="tabSize"/>
  <parameter default="true" type="boolean" name="ignoreImports"/>
 </parameters>
</check>

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

Parameters

No parameters

Example configuration

TBD

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.

Parameters

ParameterDescriptionTypeDefault Value
header Header string

Example configuration

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

Parameters

ParameterDescriptionTypeDefault Value
regex Regular expression string

Example configuration

<check enabled="true" class="org.scalastyle.file.RegexChecker" level="warning">
 <parameters>
  <parameter name="regex">(?m)^\s*$(\r|)\n^\s*$(\r|)\n</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

Parameters

No parameters

Example configuration

TBD

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

Justification

Block imports 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.ClassNamesChecker - Check that class names match a regular expression

Parameters

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

Example configuration

TBD

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).

Parameters

No parameters

Example configuration

TBD

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

Example configuration

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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 (i % 2 == 0)
} yield t

is preferred to

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

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

Parameters

No parameters

Example configuration

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

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

Justification

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

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

Parameters

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

Example configuration

TBD

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.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

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.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

Example configuration

<check enabled="true" class="org.scalastyle.scalariform.MethodLengthChecker" level="warning">
 <parameters>
  <parameter name="maxLength">50</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.NoCloneChecker - Check that classes and objects do not define the clone() method

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

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

Example configuration

TBD

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

Parameters

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

Example configuration

TBD

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

Parameters

ParameterDescriptionTypeDefault Value
maxParameters Maximum Number integer 8

Example configuration

TBD

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 }
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.

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

Parameters

No parameters

Example configuration

TBD

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

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"/>

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

vars (mutable local variables) loops 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.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"/>