Add explicit caching test for PropertiesFileTransformer

api/shadow.api

@@ -473,6 +473,10 @@ public class com/github/jengelman/gradle/plugins/shadow/transformers/IncludeReso
 	public fun transform (Lcom/github/jengelman/gradle/plugins/shadow/transformers/TransformerContext;)V
 }
 
+public abstract interface class com/github/jengelman/gradle/plugins/shadow/transformers/KeyTransformer : java/io/Serializable {
+	public abstract fun transform (Ljava/lang/String;)Ljava/lang/String;
+}
+
 public class com/github/jengelman/gradle/plugins/shadow/transformers/Log4j2PluginsCacheFileTransformer : com/github/jengelman/gradle/plugins/shadow/transformers/Transformer {
 	public fun <init> ()V
 	public fun canTransformResource (Lorg/gradle/api/file/FileTreeElement;)Z
@@ -516,15 +520,14 @@ public class com/github/jengelman/gradle/plugins/shadow/transformers/PropertiesF
 	public fun <init> (Lorg/gradle/api/model/ObjectFactory;)V
 	public fun canTransformResource (Lorg/gradle/api/file/FileTreeElement;)Z
 	public fun getCharsetName ()Lorg/gradle/api/provider/Property;
-	public fun getKeyTransformer ()Lkotlin/jvm/functions/Function1;
+	public fun getKeyTransformer ()Lorg/gradle/api/provider/Property;
 	public fun getMappings ()Lorg/gradle/api/provider/MapProperty;
 	public fun getMergeSeparator ()Lorg/gradle/api/provider/Property;
 	public fun getMergeStrategy ()Lorg/gradle/api/provider/Property;
 	public final fun getObjectFactory ()Lorg/gradle/api/model/ObjectFactory;
 	public fun getPaths ()Lorg/gradle/api/provider/SetProperty;
 	public fun hasTransformedResource ()Z
 	public fun modifyOutputStream (Lorg/apache/tools/zip/ZipOutputStream;Z)V
-	public fun setKeyTransformer (Lkotlin/jvm/functions/Function1;)V
 	public fun transform (Lcom/github/jengelman/gradle/plugins/shadow/transformers/TransformerContext;)V
 }
 

src/functionalTest/kotlin/com/github/jengelman/gradle/plugins/shadow/caching/TransformerCachingTest.kt

@@ -10,6 +10,7 @@ import com.github.jengelman.gradle.plugins.shadow.transformers.ComponentsXmlReso
 import com.github.jengelman.gradle.plugins.shadow.transformers.DontIncludeResourceTransformer
 import com.github.jengelman.gradle.plugins.shadow.transformers.GroovyExtensionModuleTransformer
 import com.github.jengelman.gradle.plugins.shadow.transformers.IncludeResourceTransformer
+import com.github.jengelman.gradle.plugins.shadow.transformers.KeyTransformer
 import com.github.jengelman.gradle.plugins.shadow.transformers.Log4j2PluginsCacheFileTransformer
 import com.github.jengelman.gradle.plugins.shadow.transformers.ManifestAppenderTransformer
 import com.github.jengelman.gradle.plugins.shadow.transformers.ManifestResourceTransformer
@@ -145,6 +146,40 @@ class TransformerCachingTest : BaseCachingTest() {
     assertions("baz")
   }
 
+  @Test
+  fun shadowJarIsCachedCorrectlyWhenUsingPropertiesFileTransformer() {
+    val uppercaseTrans = keyTransformer("key.toUpperCase()")
+    projectScriptPath.appendText(
+      transform<PropertiesFileTransformer>(
+        transformerBlock = """
+          keyTransformer = $uppercaseTrans
+        """.trimIndent(),
+      ),
+    )
+    path("src/main/resources/foo/bar.properties").writeText("foo=bar")
+    val assertions = { key: String ->
+      assertThat(outputShadowJar).useAll {
+        containsEntries("shadow/Main.class", "foo/bar.properties")
+        getContent("foo/bar.properties").contains("$key=bar")
+      }
+    }
+
+    assertFirstExecutionSuccess()
+    assertions("FOO")
+    assertExecutionsAreCachedAndUpToDate()
+    assertions("FOO")
+
+    val prefixTrans = keyTransformer("'prefix.' + key")
+
+    val replaced = projectScriptPath.readText().replace(uppercaseTrans, prefixTrans)
+    projectScriptPath.writeText(replaced)
+
+    assertFirstExecutionSuccess()
+    assertions("prefix.foo")
+    assertExecutionsAreCachedAndUpToDate()
+    assertions("prefix.foo")
+  }
+
   @ParameterizedTest
   @MethodSource("transformerConfigProvider")
   fun shadowJarIsCachedCorrectlyWhenUsingOtherTransformers(pair: Pair<String, KClass<*>>) {
@@ -187,7 +222,17 @@ class TransformerCachingTest : BaseCachingTest() {
       "" to Log4j2PluginsCacheFileTransformer::class,
       "" to ManifestAppenderTransformer::class,
       "" to ManifestResourceTransformer::class,
-      "{ keyTransformer = { it.toLowerCase() } }" to PropertiesFileTransformer::class,
     )
+
+    fun keyTransformer(trans: String): String {
+      return """
+        new ${KeyTransformer::class.java.name}() {
+          @Override
+          public String transform(String key) {
+            return $trans
+          }
+        }
+      """.trimIndent()
+    }
   }
 }

src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/transformers/PropertiesFileTransformer.kt

@@ -7,6 +7,7 @@ import com.github.jengelman.gradle.plugins.shadow.internal.property
 import com.github.jengelman.gradle.plugins.shadow.internal.setProperty
 import com.github.jengelman.gradle.plugins.shadow.transformers.PropertiesFileTransformer.MergeStrategy
 import java.io.InputStream
+import java.io.Serializable
 import java.nio.charset.Charset
 import java.util.Properties
 import javax.inject.Inject
@@ -123,10 +124,9 @@ public open class PropertiesFileTransformer @Inject constructor(
   @get:Input
   public open val charsetName: Property<String> = objectFactory.property(Charsets.ISO_8859_1.name())
 
-  @Transient // Input property should be Serializable, but we don't want to serialize the lambda.
   @get:Optional
   @get:Input
-  public open var keyTransformer: ((String) -> String)? = null
+  public open val keyTransformer: Property<KeyTransformer> = objectFactory.property()
 
   override fun canTransformResource(element: FileTreeElement): Boolean {
     val mappings = mappings.get()
@@ -176,12 +176,10 @@ public open class PropertiesFileTransformer @Inject constructor(
   }
 
   private fun transformKeys(properties: Properties): CleanProperties {
-    if (keyTransformer == null) {
-      return properties as CleanProperties
-    }
+    val keyTransformer = keyTransformer.orNull ?: return properties as CleanProperties
     val result = CleanProperties()
     properties.forEach { (key, value) ->
-      result[keyTransformer!!(key as String)] = value
+      result[keyTransformer.transform(key as String)] = value
     }
     return result
   }
@@ -255,3 +253,7 @@ public open class PropertiesFileTransformer @Inject constructor(
     private const val PROPERTIES_SUFFIX = ".properties"
   }
 }
+
+public fun interface KeyTransformer : Serializable {
+  public fun transform(key: String): String
+}

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

@@ -131,7 +131,7 @@ class PropertiesFileTransformerTest : BaseTransformerTest<PropertiesFileTransfor
     expectedOutput: Map<String, String>,
   ) {
     transformer.mergeStrategy.set(MergeStrategy.Append)
-    transformer.keyTransformer = keyTransformer
+    transformer.keyTransformer.set(KeyTransformer { keyTransformer(it) })
 
     if (transformer.canTransformResource(path)) {
       transformer.transform(context(path, input1))