Detekt Setup for Kotlin Code Style Checking

Setting Up Detekt for Kotlin Code Style Checking

Detekt is a static analyzer for Kotlin code. It finds code smells, checks function complexity, detects potentially unsafe code (unsafe !!, magic numbers, empty catch blocks). For Android projects, it works alongside Android Lint — they complement each other: Lint knows Android specifics (incorrect Context usage, memory leaks), Detekt — Kotlin idioms.

Connecting to Gradle

// build.gradle.kts (project level)
plugins {
    id("io.gitlab.arturbosch.detekt") version "1.23.7"
}

detekt {
    config.setFrom(files("$rootDir/detekt.yml"))
    buildUponDefaultConfig = true
    allRules = false
    baseline = file("$rootDir/detekt-baseline.xml")
}

dependencies {
    detektPlugins("io.gitlab.arturbosch.detekt:detekt-formatting:1.23.7")
    detektPlugins("com.twitter.compose.rules:detekt:0.0.26")  // Compose-specific rules
}

detektPlugins("io.gitlab.arturbosch.detekt:detekt-formatting") adds formatting via ktlint under the hood.

detekt.yml Configuration

build:
  maxIssues: 0
  excludeCorrectable: false

complexity:
  LongMethod:
    threshold: 50
  CyclomaticComplexMethod:
    threshold: 15
  LongParameterList:
    threshold: 6
    ignoreDefaultParameters: true
  TooManyFunctions:
    thresholdInFiles: 20
    thresholdInClasses: 15

style:
  MagicNumber:
    ignoreNumbers:
      - '-1'
      - '0'
      - '1'
      - '2'
    ignoreEnums: true
    ignoreConstantDeclaration: true
  UnusedPrivateMember:
    active: true

potential-bugs:
  UnsafeCallOnNullableType:
    active: true
  UnreachableCode:
    active: true

exceptions:
  SwallowedException:
    active: true
  TooGenericExceptionCaught:
    active: true
    exceptionNames:
      - Exception
      - Throwable

Baseline

On existing projects, Detekt finds hundreds of violations. Running with maxIssues: 0 from scratch is unrealistic. Baseline fixes current state:

./gradlew detektBaseline

Creates detekt-baseline.xml with all existing violations. Detekt will complain only about new violations in new code. Baseline is committed to repository, gradually cleaned up during refactoring.

Running in CI

- name: Run Detekt
  run: ./gradlew detekt

- name: Upload Detekt Report
  uses: github/codeql-action/upload-sarif@v3
  if: always()
  with:
    sarif_file: build/reports/detekt/detekt.sarif

SARIF format displays violations directly in GitHub Code Review as annotations. if: always() — upload report even if detekt fails, so we see violations in PR.

Compose-specific Rules

For Jetpack Compose projects add twitter-compose-rules:

detektPlugins("com.twitter.compose.rules:detekt:0.0.26")

Rules check: @Composable functions without @Preview, unstable parameters in @Composable, remember usage without keys where keys are needed. Real issues Android Lint doesn't cover.

Timeline: 1 day. Cost is calculated individually.