Default failOnDuplicateEntries to true

docs/configuration/merging/README.md

@@ -102,8 +102,8 @@ Alternatively, you can follow these steps:
 
 Optional steps:
 
-- Enable [`ShadowJar.failOnDuplicateEntries`][ShadowJar.failOnDuplicateEntries] to check duplicate entries in the final JAR.
-  This can also ensure the regressions are caught in the future.
+- [`ShadowJar.failOnDuplicateEntries`][ShadowJar.failOnDuplicateEntries] is enabled by default to check duplicate entries in the final JAR.
+  This can also ensure the regressions are caught in the future. Disable it if you want to allow duplicate entries.
 - Use [Diffuse](https://github.com/JakeWharton/diffuse) to diff the JARs.
 
 Here are some examples:
@@ -144,8 +144,8 @@ Here are some examples:
     }
 
     tasks.shadowJar {
-      // Optional step.
-      failOnDuplicateEntries = true
+      // Optional step: disable it if you want to allow duplicate entries.
+      failOnDuplicateEntries = false
     }
     ```
 
@@ -185,8 +185,8 @@ Here are some examples:
     }
 
     tasks.named('shadowJar', com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar) {
-      // Optional step.
-      failOnDuplicateEntries = true
+      // Optional step: disable it if you want to allow duplicate entries.
+      failOnDuplicateEntries = false
     }
     ```
 

src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/tasks/ShadowJar.kt

@@ -219,14 +219,14 @@ public abstract class ShadowJar : Jar() {
    * - Usually used with setting [getDuplicatesStrategy] to [INCLUDE] or [WARN].
    * - It provides a stricter check before the JAR is created.
    *
-   * Defaults to `false`.
+   * Defaults to `true`.
    */
   @get:Input
   @get:Option(
     option = "fail-on-duplicate-entries",
     description = "Fails build if the ZIP entries in the shadowed JAR are duplicate.",
   )
-  public open val failOnDuplicateEntries: Property<Boolean> = objectFactory.property(false)
+  public open val failOnDuplicateEntries: Property<Boolean> = objectFactory.property(true)
 
   /**
    * Adds the [java.util.jar.Attributes.Name.MULTI_RELEASE] attribute to the manifest of the shadow

src/test/kotlin/com/github/jengelman/gradle/plugins/shadow/ShadowPropertiesTest.kt

@@ -148,7 +148,7 @@ class ShadowPropertiesTest {
         assertThat(addMultiReleaseAttribute.get()).isTrue()
         assertThat(enableAutoRelocation.get()).isFalse()
         assertThat(enableKotlinModuleRemapping.get()).isTrue()
-        assertThat(failOnDuplicateEntries.get()).isFalse()
+        assertThat(failOnDuplicateEntries.get()).isTrue()
         assertThat(minimizeJar.get()).isFalse()
         assertThat(mainClass.orNull).isNull()