Index: subprojects/core/src/integTest/groovy/org/gradle/api/internal/changedetection/state/TaskTypeUpToDateIntegrationTest.groovy
===================================================================
diff -u -N -r39e6b15eef5750dc0074140335f8ee52ab6e46bf -ra41dfa4e9a7f46c60f15f8eaca40156c51905998
--- subprojects/core/src/integTest/groovy/org/gradle/api/internal/changedetection/state/TaskTypeUpToDateIntegrationTest.groovy	(.../TaskTypeUpToDateIntegrationTest.groovy)	(revision 39e6b15eef5750dc0074140335f8ee52ab6e46bf)
+++ subprojects/core/src/integTest/groovy/org/gradle/api/internal/changedetection/state/TaskTypeUpToDateIntegrationTest.groovy	(.../TaskTypeUpToDateIntegrationTest.groovy)	(revision a41dfa4e9a7f46c60f15f8eaca40156c51905998)
@@ -16,9 +16,13 @@
 
 package org.gradle.api.internal.changedetection.state
 
+import org.gradle.api.tasks.incremental.IncrementalTaskInputs
 import org.gradle.integtests.fixtures.AbstractIntegrationSpec
+import org.gradle.work.InputChanges
 import spock.lang.Issue
+import spock.lang.Unroll
 
+@Unroll
 class TaskTypeUpToDateIntegrationTest extends AbstractIntegrationSpec {
 
     def "task is up-to-date after unrelated change to build script"() {
@@ -176,6 +180,33 @@
         then: skipped(":copy")
     }
 
+    @Issue("https://github.com/gradle/gradle/issues/9723")
+    def "declaring a task action receiving #incrementalChangesType without declaring outputs is deprecated"() {
+        def input = file('input.txt').createFile()
+        buildFile << """
+            class IncrementalTask extends DefaultTask {
+                @InputFile File input
+             
+                @TaskAction execute(${incrementalChangesType} inputChanges) {
+                }
+            }   
+            
+            task noOutput(type: IncrementalTask) {
+                input = file('${input.name}')
+            }
+        """
+
+        when:
+        executer.expectDeprecationWarning()
+        run 'noOutput'
+        then:
+        outputContains("Using the incremental task API without declaring any outputs has been deprecated. This is scheduled to be removed in Gradle 6.0. Please declare output files for your task or use `task.upToDateWhen { true }`.")
+        noneSkipped()
+
+        where:
+        incrementalChangesType << [IncrementalTaskInputs.simpleName, InputChanges.simpleName]
+    }
+
     private static String declareSimpleCopyTask(boolean modification = false) {
         """
             ${declareSimpleCopyTaskType(modification)}