Quality Expert

Quality Expert Skill

Overview

Code quality tools for KMP:

• Detekt: Static analysis (complexity, style, bugs)
• Spotless/ktlint: Formatting
• Custom Lint: Project-specific rules
• Architecture Rules: Module boundary enforcement

Detekt Setup

Installation

// build.gradle.kts (root)
plugins {
    id("io.gitlab.arturbosch.detekt") version "1.23.8"
}

// Configure for all subprojects
subprojects {
    apply(plugin = "io.gitlab.arturbosch.detekt")

    detekt {
        buildUponDefaultConfig = true
        config.setFrom(files("${rootProject.projectDir}/config/detekt/detekt.yml"))
        baseline = file("${rootProject.projectDir}/config/detekt/baseline.xml")

        // KMP support
        source.setFrom(
            "src/commonMain/kotlin",
            "src/androidMain/kotlin",
            "src/iosMain/kotlin",
            "src/desktopMain/kotlin",
        )
    }

    dependencies {
        detektPlugins("io.gitlab.arturbosch.detekt:detekt-formatting:1.23.8")
        detektPlugins("io.gitlab.arturbosch.detekt:detekt-rules-libraries:1.23.8")
        detektPlugins("io.nlopez.compose.rules:detekt:0.4.22") // Compose rules
    }
}

Configuration File

# config/detekt/detekt.yml

build:
  maxIssues: 0
  excludeCorrectable: false
  weights:
    complexity: 2
    formatting: 1
    LongParameterList: 1
    style: 1
    comments: 1

config:
  validation: true
  warningsAsErrors: true
  checkExhaustiveness: true

processors:
  active: true
  exclude:
    - 'DetektProgressListener'

console-reports:
  active: true

output-reports:
  active: true
  exclude:
    - 'TxtOutputReport'
    - 'XmlOutputReport'

# Rule sets
complexity:
  active: true
  ComplexCondition:
    active: true
    threshold: 4
  ComplexMethod:
    active: true
    threshold: 15
  LargeClass:
    active: true
    threshold: 600
  LongMethod:
    active: true
    threshold: 60
  LongParameterList:
    active: true
    functionThreshold: 6
    constructorThreshold: 8
    ignoreDefaultParameters: true
    ignoreDataClasses: true
    ignoreAnnotatedParameter: ['Inject', 'Assisted', 'Provides']
  NestedBlockDepth:
    active: true
    threshold: 4
  TooManyFunctions:
    active: true
    thresholdInFiles: 15
    thresholdInClasses: 15
    thresholdInInterfaces: 15
    thresholdInObjects: 15
    thresholdInEnums: 15

coroutines:
  active: true
  GlobalCoroutineUsage:
    active: true
  InjectDispatcher:
    active: true
    dispatcherNames:
      - 'IO'
      - 'Default'
      - 'Unconfined'
  RedundantSuspendModifier:
    active: true
  SleepInsteadOfDelay:
    active: true
  SuspendFunWithCoroutineScopeReceiver:
    active: true
  SuspendFunSwallowedCancellation:
    active: true

empty-blocks:
  active: true
  EmptyCatchBlock:
    active: true
    allowedExceptionNameRegex: '_|(ignore|expected).*'
  EmptyClassBlock:
    active: true
  EmptyDefaultConstructor:
    active: true
  EmptyDoWhileBlock:
    active: true
  EmptyElseBlock:
    active: true
  EmptyFinallyBlock:
    active: true
  EmptyForBlock:
    active: true
  EmptyFunctionBlock:
    active: true
    ignoreOverridden: true
  EmptyIfBlock:
    active: true
  EmptyInitBlock:
    active: true
  EmptyKtFile:
    active: true
  EmptySecondaryConstructor:
    active: true
  EmptyTryBlock:
    active: true
  EmptyWhenBlock:
    active: true
  EmptyWhileBlock:
    active: true

exceptions:
  active: true
  ExceptionRaisedInUnexpectedLocation:
    active: true
    methodNames:
      - 'equals'
      - 'finalize'
      - 'hashCode'
      - 'toString'
  InstanceOfCheckForException:
    active: true
  NotImplementedDeclaration:
    active: true
  ObjectExtendsThrowable:
    active: true
  PrintStackTrace:
    active: true
  RethrowCaughtException:
    active: true
  ReturnFromFinally:
    active: true
  SwallowedException:
    active: true
    ignoredExceptionTypes:
      - 'InterruptedException'
      - 'MalformedURLException'
      - 'NumberFormatException'
      - 'ParseException'
    allowedExceptionNameRegex: '_|(ignore|expected).*'
  ThrowingExceptionFromFinally:
    active: true
  ThrowingExceptionInMain:
    active: false
  ThrowingExceptionsWithoutMessageOrCause:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
    exceptions:
      - 'ArrayIndexOutOfBoundsException'
      - 'Exception'
      - 'IllegalArgumentException'
      - 'IllegalMonitorStateException'
      - 'IllegalStateException'
      - 'IndexOutOfBoundsException'
      - 'NullPointerException'
      - 'RuntimeException'
      - 'Throwable'
  ThrowingNewInstanceOfSameException:
    active: true
  TooGenericExceptionCaught:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
    exceptionNames:
      - 'ArrayIndexOutOfBoundsException'
      - 'Error'
      - 'Exception'
      - 'IllegalMonitorStateException'
      - 'IndexOutOfBoundsException'
      - 'NullPointerException'
      - 'RuntimeException'
      - 'Throwable'
    allowedExceptionNameRegex: '_|(ignore|expected).*'
  TooGenericExceptionThrown:
    active: true
    exceptionNames:
      - 'Error'
      - 'Exception'
      - 'RuntimeException'
      - 'Throwable'

naming:
  active: true
  ClassNaming:
    active: true
    classPattern: '[A-Z][a-zA-Z0-9]*'
  ConstructorParameterNaming:
    active: true
    parameterPattern: '[a-z][A-Za-z0-9]*'
    privateParameterPattern: '[a-z][A-Za-z0-9]*'
    excludeClassPattern: '$^'
  EnumNaming:
    active: true
    enumEntryPattern: '[A-Z][_a-zA-Z0-9]*'
  ForbiddenClassName:
    active: false
  FunctionMaxLength:
    active: true
    maximumFunctionNameLength: 50
  FunctionMinLength:
    active: false
  FunctionNaming:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
    functionPattern: '[a-z][a-zA-Z0-9]*'
    excludeClassPattern: '$^'
    # Allow Compose naming
    ignoreAnnotated: ['Composable']
  FunctionParameterNaming:
    active: true
    parameterPattern: '[a-z][A-Za-z0-9]*'
    excludeClassPattern: '$^'
  InvalidPackageDeclaration:
    active: true
    rootPackage: 'com.app'
  LambdaParameterNaming:
    active: true
    parameterPattern: '[a-z][A-Za-z0-9]*|_'
  MatchingDeclarationName:
    active: true
    mustBeFirst: true
  MemberNameEqualsClassName:
    active: true
    ignoreOverridden: true
  NoNameShadowing:
    active: true
  NonBooleanPropertyPrefixedWithIs:
    active: true
  ObjectPropertyNaming:
    active: true
    constantPattern: '[A-Za-z][_A-Za-z0-9]*'
    propertyPattern: '[A-Za-z][_A-Za-z0-9]*'
    privatePropertyPattern: '[A-Za-z][_A-Za-z0-9]*'
  PackageNaming:
    active: true
    packagePattern: '[a-z]+(\.[a-z][A-Za-z0-9]*)*'
  TopLevelPropertyNaming:
    active: true
    constantPattern: '[A-Z][_A-Z0-9]*'
    propertyPattern: '[A-Za-z][_A-Za-z0-9]*'
    privatePropertyPattern: '_?[A-Za-z][_A-Za-z0-9]*'
  VariableMaxLength:
    active: true
    maximumVariableNameLength: 40
  VariableMinLength:
    active: true
    minimumVariableNameLength: 1
  VariableNaming:
    active: true
    variablePattern: '[a-z][A-Za-z0-9]*'
    privateVariablePattern: '[a-z][A-Za-z0-9]*'
    excludeClassPattern: '$^'

performance:
  active: true
  ArrayPrimitive:
    active: true
  CouldBeSequence:
    active: true
    threshold: 3
  ForEachOnRange:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
  SpreadOperator:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
  UnnecessaryPartOfBinaryExpression:
    active: true
  UnnecessaryTemporaryInstantiation:
    active: true

potential-bugs:
  active: true
  AvoidReferentialEquality:
    active: true
  CastToNullableType:
    active: true
  Deprecation:
    active: false
  DontDowncastCollectionTypes:
    active: true
  DoubleMutabilityForCollection:
    active: true
  ElseCaseInsteadOfExhaustiveWhen:
    active: true
  EqualsAlwaysReturnsTrueOrFalse:
    active: true
  EqualsWithHashCodeExist:
    active: true
  ExitOutsideMain:
    active: true
  ExplicitGarbageCollectionCall:
    active: true
  HasPlatformType:
    active: true
  IgnoredReturnValue:
    active: true
    restrictToConfig: true
    returnValueAnnotations:
      - 'CheckResult'
      - 'CheckReturnValue'
    ignoreReturnValueAnnotations:
      - 'CanIgnoreReturnValue'
    returnValueTypes:
      - 'arrow.core.Either'
      - 'arrow.core.Option'
      - 'kotlin.Result'
  ImplicitDefaultLocale:
    active: true
  ImplicitUnitReturnType:
    active: true
  InvalidRange:
    active: true
  IteratorHasNextCallsNextMethod:
    active: true
  IteratorNotThrowingNoSuchElementException:
    active: true
  LateinitUsage:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
    ignoreAnnotated: ['Inject']
  MapGetWithNotNullAssertionOperator:
    active: true
  MissingPackageDeclaration:
    active: true
  NullCheckOnMutableProperty:
    active: true
  NullableToStringCall:
    active: true
  PropertyUsedBeforeDeclaration:
    active: true
  UnconditionalJumpStatementInLoop:
    active: true
  UnnecessaryNotNullCheck:
    active: true
  UnnecessaryNotNullOperator:
    active: true
  UnnecessarySafeCall:
    active: true
  UnreachableCatchBlock:
    active: true
  UnreachableCode:
    active: true
  UnsafeCallOnNullableType:
    active: true
    excludes: ['**/test/**', '**/androidTest/**']
  UnsafeCast:
    active: true
  UnusedUnaryOperator:
    active: true
  UselessPostfixExpression:
    active: true
  WrongEqualsTypeParameter:
    active: true

style:
  active: true
  AlsoCouldBeApply:
    active: true
  BracesOnIfStatements:
    active: true
    singleLine: 'never'
    multiLine: 'always'
  BracesOnWhenStatements:
    active: true
    singleLine: 'necessary'
    multiLine: 'consistent'
  CanBeNonNullable:
    active: true
  CascadingCallWrapping:
    active: true
    includeElvis: true
  ClassOrdering:
    active: true
  CollapsibleIfStatements:
    active: true
  DataClassContainsFunctions:
    active: false
  DataClassShouldBeImmutable:
    active: true
  DestructuringDeclarationWithTooManyEntries:
    active: true
    maxDestructuringEntries: 4
  EqualsNullCall:
    active: true
  EqualsOnSignatureLine:
    active: true
  ExplicitCollectionElementAccessMethod:
    active: true
  ExplicitItLambdaParameter:
    active: true
  ExpressionBodySyntax:
    active: true
    includeLineWrapping: false
  ForbiddenAnnotation:
    active: true
    annotations:
      - reason: 'Use @Inject instead'
        value: 'javax.inject.Inject'
  ForbiddenComment:
    active: true
    values:
      - reason: 'Remove TODO before merging'
        value: 'TODO:'
      - reason: 'Remove FIXME before merging'
        value: 'FIXME:'
      - reason: 'Remove STOPSHIP before merging'
        value: 'STOPSHIP'
    allowedPatterns: 'TODO\\(\\w+\\):'  # Allow TODO(username):
  ForbiddenImport:
    active: true
    imports:
      - value: 'java.util.stream.*'
        reason: 'Use Kotlin stdlib instead'
  ForbiddenMethodCall:
    active: true
    methods:
      - reason: 'Use println for debug only'
        value: 'kotlin.io.println'
      - reason: 'Use proper logging'
        value: 'java.io.PrintStream.println'
  ForbiddenVoid:
    active: true
    ignoreOverridden: false
    ignoreUsageInGenerics: false
  FunctionOnlyReturningConstant:
    active: true
    ignoreOverridableFunction: true
    ignoreActualFunction: true
    excludedFunctions: []
  LoopWithTooManyJumpStatements:
    active: true
    maxJumpCount: 2
  MagicNumber:
    active: true
    excludes: ['**/test/**', '**/androidTest/**', '**/*Test.kt']
    ignoreNumbers:
      - '-1'
      - '0'
      - '1'
      - '2'
    ignoreHashCodeFunction: true
    ignorePropertyDeclaration: true
    ignoreLocalVariableDeclaration: false
    ignoreConstantDeclaration: true
    ignoreCompanionObjectPropertyDeclaration: true
    ignoreAnnotation: true
    ignoreNamedArgument: true
    ignoreEnums: true
    ignoreRanges: true
    ignoreExtensionFunctions: true
  MandatoryBracesLoops:
    active: true
  MaxChainedCallsOnSameLine:
    active: true
    maxChainedCalls: 5
  MaxLineLength:
    active: true
    maxLineLength: 120
    excludePackageStatements: true
    excludeImportStatements: true
    excludeCommentStatements: true
    excludeRawStrings: true
  MayBeConst:
    active: true
  ModifierOrder:
    active: true
  MultilineLambdaItParameter:
    active: true
  MultilineRawStringIndentation:
    active: true
    indentSize: 4
    trimmingMethod: 'trimIndent'
  NestedClassesVisibility:
    active: true
  NewLineAtEndOfFile:
    active: true
  NoTabs:
    active: true
  NullableBooleanCheck:
    active: true
  ObjectLiteralToLambda:
    active: true
  OptionalAbstractKeyword:
    active: true
  OptionalUnit:
    active: false
  PreferToOverPairSyntax:
    active: true
  ProtectedMemberInFinalClass:
    active: true
  RedundantExplicitType:
    active: true
  RedundantHigherOrderMapUsage:
    active: true
  RedundantVisibilityModifierRule:
    active: true
  ReturnCount:
    active: true
    max: 4
    excludedFunctions:
      - 'equals'
    excludeLabeled: true
    excludeReturnFromLambda: true
    excludeGuardClauses: true
  SafeCast:
    active: true
  SerialVersionUIDInSerializableClass:
    active: true
  SpacingBetweenPackageAndImports:
    active: true
  StringShouldBeRawString:
    active: true
    maxEscapedCharacterCount: 2
    ignoredCharacters: []
  ThrowsCount:
    active: true
    max: 3
    excludeGuardClauses: true
  TrailingWhitespace:
    active: true
  TrimMultilineRawString:
    active: true
    trimmingMethod: 'trimIndent'
  UnderscoresInNumericLiterals:
    active: true
    acceptableLength: 4
    allowNonStandardGrouping: false
  UnnecessaryAbstractClass:
    active: true
  UnnecessaryAnnotationUseSiteTarget:
    active: true
  UnnecessaryApply:
    active: true
  UnnecessaryBackticks:
    active: true
  UnnecessaryBracesAroundTrailingLambda:
    active: true
  UnnecessaryFilter:
    active: true
  UnnecessaryInheritance:
    active: true
  UnnecessaryInnerClass:
    active: true
  UnnecessaryLet:
    active: true
  UnnecessaryParentheses:
    active: true
    allowForUnclearPrecedence: false
  UntilInsteadOfRangeTo:
    active: true
  UnusedImports:
    active: true
  UnusedParameter:
    active: true
    allowedNames: '_|ignored|expected|serialVersionUID'
  UnusedPrivateClass:
    active: true
  UnusedPrivateMember:
    active: true
    allowedNames: '(_|ignored|expected|serialVersionUID)'
  UnusedPrivateProperty:
    active: true
    allowedNames: '_|ignored|expected|serialVersionUID'
  UseAnyOrNoneInsteadOfFind:
    active: true
  UseArrayLiteralsInAnnotations:
    active: true
  UseCheckNotNull:
    active: true
  UseCheckOrError:
    active: true
  UseDataClass:
    active: true
    allowVars: false
  UseEmptyCounterpart:
    active: true
  UseIfEmptyOrIfBlank:
    active: true
  UseIfInsteadOfWhen:
    active: true
    minimumBranches: 2
  UseIsNullOrEmpty:
    active: true
  UseLet:
    active: true
  UseOrEmpty:
    active: true
  UseRequire:
    active: true
  UseRequireNotNull:
    active: true
  UseSumOfInsteadOfFlatMapSize:
    active: true
  UselessCallOnNotNull:
    active: true
  UtilityClassWithPublicConstructor:
    active: true
  VarCouldBeVal:
    active: true
    ignoreLateinitVar: false
  WildcardImport:
    active: true
    excludeImports:
      - 'java.util.*'
      - 'kotlinx.coroutines.*'

Spotless / ktlint Setup

// build.gradle.kts (root)
plugins {
    id("com.diffplug.spotless") version "8.1.0"
}

spotless {
    kotlin {
        target("**/*.kt")
        targetExclude("**/build/**/*.kt")

        ktlint("1.8.0")
            .setEditorConfigPath("${rootProject.projectDir}/.editorconfig")
            .editorConfigOverride(
                mapOf(
                    "ktlint_standard_filename" to "disabled",
                    "ktlint_standard_function-naming" to "disabled",  // Compose
                    "ktlint_standard_property-naming" to "disabled",  // Constants
                    "ktlint_standard_trailing-comma-on-call-site" to "disabled",
                    "ktlint_standard_trailing-comma-on-declaration-site" to "disabled",
                )
            )

        trimTrailingWhitespace()
        indentWithSpaces(4)
        endWithNewline()
    }

    kotlinGradle {
        target("**/*.gradle.kts")
        ktlint("1.8.0")
    }
}

EditorConfig

# .editorconfig
root = true

[*]
charset = utf-8
end_of_line = lf
indent_size = 4
indent_style = space
insert_final_newline = true
max_line_length = 120
tab_width = 4
trim_trailing_whitespace = true

[*.{kt,kts}]
ij_kotlin_allow_trailing_comma = true
ij_kotlin_allow_trailing_comma_on_call_site = true
ij_kotlin_imports_layout = *,java.**,javax.**,kotlin.**,^

# Compose
ktlint_function_naming_ignore_when_annotated_with = Composable

Compose Detekt Rules

# Additional rules for Compose in detekt.yml

compose:
  active: true
  ComposableAnnotationNaming:
    active: true
  ComposableNaming:
    active: true
  CompositionLocalAllowlist:
    active: true
    allowedCompositionLocals:
      - LocalExtendedColors
      - LocalSpacing
  ContentEmitterReturningValues:
    active: true
  ModifierClickableOrder:
    active: true
  ModifierComposable:
    active: true
  ModifierMissing:
    active: true
  ModifierNotDefaultParam:
    active: true
  ModifierReused:
    active: true
  ModifierWithoutDefault:
    active: true
  MultipleEmitters:
    active: true
  MutableParams:
    active: true
  PreviewNaming:
    active: true
  PreviewPublic:
    active: true
  RememberMissing:
    active: true
  UnstableCollections:
    active: true
  ViewModelForwarding:
    active: true
  ViewModelInjection:
    active: true

Module Boundary Rules

// build-logic/src/main/kotlin/ModuleBoundaryPlugin.kt

class ModuleBoundaryPlugin : Plugin<Project> {
    override fun apply(target: Project) = with(target) {
        afterEvaluate {
            val modulePath = path
            
            // Define allowed dependencies per layer
            val allowedDependencies = when {
                modulePath.startsWith(":features:") -> setOf(
                    ":core:common",
                    ":core:ui", 
                    ":domain:models",
                    ":domain:usecases",
                )
                modulePath.startsWith(":domain:usecases") -> setOf(
                    ":core:common",
                    ":domain:models",
                    ":data:repositories",
                )
                modulePath.startsWith(":domain:models") -> setOf(
                    ":core:common",
                )
                modulePath.startsWith(":data:") -> setOf(
                    ":core:common",
                    ":core:network",
                    ":core:database",
                    ":domain:models",
                )
                else -> null
            }
            
            allowedDependencies?.let { allowed ->
                configurations.all {
                    resolutionStrategy.eachDependency {
                        if (requested.group == rootProject.name) {
                            val depPath = ":${requested.name}"
                            if (depPath !in allowed && !depPath.startsWith(modulePath)) {
                                throw GradleException(
                                    "Module $modulePath cannot depend on $depPath. " +
                                    "Allowed: $allowed"
                                )
                            }
                        }
                    }
                }
            }
        }
    }
}

Gradle Quality Tasks

// build.gradle.kts (root)

// Combined quality check
tasks.register("quality") {
    group = "verification"
    description = "Runs all quality checks"
    
    dependsOn("spotlessCheck")
    dependsOn("detekt")
    dependsOn(subprojects.mapNotNull { it.tasks.findByName("lint") })
}

// Auto-fix task
tasks.register("qualityFix") {
    group = "verification"
    description = "Fixes auto-fixable quality issues"
    
    dependsOn("spotlessApply")
}

// Pre-commit hook installer
tasks.register("installGitHooks") {
    group = "setup"
    description = "Installs git hooks"
    
    doLast {
        val hooksDir = file(".git/hooks")
        val preCommit = file("$hooksDir/pre-commit")
        
        preCommit.writeText("""
            #!/bin/bash
            echo "Running quality checks..."
            ./gradlew spotlessCheck detekt --daemon
            
            if [ $? -ne 0 ]; then
                echo "Quality checks failed. Run './gradlew qualityFix' to auto-fix."
                exit 1
            fi
        """.trimIndent())
        
        preCommit.setExecutable(true)
        println("Git hooks installed!")
    }
}

CI Integration

# .github/workflows/quality.yml
name: Quality

on:
  pull_request:
  push:
    branches: [main]

jobs:
  quality:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - name: Setup JDK
        uses: actions/setup-java@v4
        with:
          java-version: '17'
          distribution: 'temurin'
      
      - name: Check formatting
        run: ./gradlew spotlessCheck
      
      - name: Run Detekt
        run: ./gradlew detekt
      
      - name: Upload Detekt report
        if: failure()
        uses: actions/upload-artifact@v4
        with:
          name: detekt-report
          path: '**/build/reports/detekt/'

References

• Detekt: https://detekt.dev/
• Detekt Rules: https://detekt.dev/docs/rules/
• ktlint: https://pinterest.github.io/ktlint/
• Spotless: https://github.com/diffplug/spotless
• Compose Rules: https://mrmans0n.github.io/compose-rules/

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