Document how to create a common baseline file for multi module gradle projects - Closes #2100 (#2140)

build.gradle.kts

@@ -1,6 +1,7 @@
 import com.jfrog.bintray.gradle.BintrayExtension
 import groovy.lang.GroovyObject
 import io.gitlab.arturbosch.detekt.Detekt
+import io.gitlab.arturbosch.detekt.DetektCreateBaselineTask
 import org.gradle.api.tasks.testing.logging.TestExceptionFormat
 import org.gradle.api.tasks.testing.logging.TestLogEvent
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
@@ -347,3 +348,17 @@ val detektAll by tasks.registering(Detekt::class) {
         txt.enabled = false
     }
 }
+
+val detektProjectBaseline by tasks.registering(DetektCreateBaselineTask::class) {
+    description = "Overrides current baseline."
+    buildUponDefaultConfig.set(true)
+    ignoreFailures.set(true)
+    parallel.set(true)
+    setSource(files(rootDir))
+    config.setFrom(files("$rootDir/config/detekt/detekt.yml"))
+    baseline.set(file("$rootDir/config/detekt/baseline.xml"))
+    include("**/*.kt")
+    include("**/*.kts")
+    exclude("**/resources/**")
+    exclude("**/build/**")
+}

detekt-cli/src/test/kotlin/io/gitlab/arturbosch/detekt/cli/MainSpec.kt

@@ -25,7 +25,7 @@ class MainSpec : Spek({
                     emptyArray()
                 ).forEach { args ->
 
-                    val expectedRunnerClass = when  {
+                    val expectedRunnerClass = when {
                         args.contains("--generate-config") -> ConfigExporter::class
                         args.contains("--run-rule") -> SingleRuleRunner::class
                         args.contains("--print-ast") -> AstPrinter::class
@@ -41,5 +41,4 @@ class MainSpec : Spek({
             }
         }
     }
-
 })

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/invoke/DetektInvoker.kt

@@ -66,7 +66,7 @@ private class DefaultCliInvoker(private val project: Project) : DetektInvoker {
                 throw GradleException("MaxIssues or failThreshold count was reached.")
             }
             INVALID_CONFIG -> throw GradleException("Invalid detekt configuration file detected.")
-            else -> throw GradleException("Unexpected detekt exit with code '${exitValue}'.")
+            else -> throw GradleException("Unexpected detekt exit with code '$exitValue'.")
         }
     }
 

docs/pages/baseline.md

@@ -31,7 +31,68 @@ the `--report txt:path/to/report` cli flag.
 </SmellBaseline>
 ```
 
+#### Gradle
+
 If you are using the gradle-plugin run the `detektBaseline` task to generate yourself a `baseline.xml`.
+This will create one baseline file per Gradle module.
+As this might not be the desired behavior for a multi module project, think about implementing
+a custom meta baseline task:
+
+Gradle-DSL
+
+```gradle
+subprojects {
+    detekt {
+        // ...
+        baseline = file("${rootProject.projectDir}/config/baseline.xml")
+        // ...
+    }
+}
+
+task detektProjectBaseline(type: io.gitlab.arturbosch.detekt.DetektCreateBaselineTask) {
+    description = "Overrides current baseline."
+    ignoreFailures.set(true)
+    parallel.set(true)
+    buildUponDefaultConfig.set(true)
+    setSource(files(rootDir))
+    config.setFrom(files("$rootDir/config/detekt/detekt.yml"))
+    baseline.set(file("$rootDir/config/detekt/baseline.xml"))
+    include("**/*.kt")
+    include("**/*.kts")
+    exclude("**/resources/**")
+    exclude("**/build/**")
+}
+
+```
+
+Kotlin-DSL
+
+```kotlin
+subprojects {
+    detekt {
+        // ...
+        baseline = file("${rootProject.projectDir}/config/baseline.xml")
+        // ...
+    }
+}
+
+val detektProjectBaseline by tasks.registering(DetektCreateBaselineTask::class) {
+    description = "Overrides current baseline."
+    buildUponDefaultConfig.set(true)
+    ignoreFailures.set(true)
+    parallel.set(true)
+    setSource(files(rootDir))
+    config.setFrom(files("$rootDir/config/detekt/detekt.yml"))
+    baseline.set(file("$rootDir/config/detekt/baseline.xml"))
+    include("**/*.kt")
+    include("**/*.kts")
+    exclude("**/resources/**")
+    exclude("**/build/**")
+}
+
+```
+
+#### FAQ
 
 Be aware that auto formatting cannot be combined with the `baseline`.
 The signatures for a `;` for example would be too ambiguous.