Incremental KAPT: when unable to process incremental changes, run non-incrementally

When analyzing incremental changes in the KAPT task, incremental compilation
can handle directory changes, Java source file changes, jar/.class file changes,
and changes to the ABI structure of the classpath. Anything else should cause
a full recompilation.

Test: KaptIncrementalWithIsolatingApt.testNonIncrementalWithUnrecognizedInputs

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/KaptIncrementalWithIsolatingApt.kt

@@ -86,6 +86,33 @@ class KaptIncrementalWithIsolatingApt : KaptIncrementalIT() {
             assertContains("Unable to use existing data, re-initializing classpath information for KAPT.")
         }
     }
+
+    @Test
+    fun testNonIncrementalWithUnrecognizedInputs() {
+        val project = getProject()
+
+        val additionalInputs = project.projectDir.resolve("additionalInputs").also { it.mkdirs() }
+        project.gradleBuildScript().appendText(
+            """
+            
+            tasks.whenTaskAdded {
+                if (it.name == "kaptKotlin") {
+                  it.getInputs().files("${additionalInputs.canonicalPath}")
+                }
+            }
+        """.trimIndent()
+        )
+
+        project.build("clean", "build") {
+            assertSuccessful()
+        }
+
+        additionalInputs.resolve("layout.xml").createNewFile()
+        project.build("build") {
+            assertSuccessful()
+            assertContains("Incremental annotation processing (apt mode): false")
+        }
+    }
 }
 
 private const val patternApt = "Processing java sources with annotation processors:"

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/KaptTask.kt

@@ -196,7 +196,22 @@ abstract class KaptTask : ConventionTask(), TaskWithLocalState {
         val startTime = System.currentTimeMillis()
 
         val previousSnapshot = if (inputs.isIncremental) {
-            ClasspathSnapshot.ClasspathSnapshotFactory.loadFrom(incAptCacheDir)
+            val loadedPrevious = ClasspathSnapshot.ClasspathSnapshotFactory.loadFrom(incAptCacheDir)
+
+            val previousAndCurrentDataFiles = lazy { loadedPrevious.getAllDataFiles() + allDataFiles }
+            val allChangesRecognized = changedFiles.all {
+                val extension = it.extension
+                if (extension.isEmpty() || extension == "java" || extension == "jar" || extension == "class") {
+                    return@all true
+                }
+                // if not a directory, Java source file, jar, or class, it has to be a structure file, in order to understand changes
+                it in previousAndCurrentDataFiles.value
+            }
+            if (allChangesRecognized) {
+                loadedPrevious
+            } else {
+                ClasspathSnapshot.ClasspathSnapshotFactory.getEmptySnapshot()
+            }
         } else {
             ClasspathSnapshot.ClasspathSnapshotFactory.getEmptySnapshot()
         }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/incremental/ClasspathSnapshot.kt

@@ -56,6 +56,8 @@ open class ClasspathSnapshot protected constructor(
         fun getEmptySnapshot() = UnknownSnapshot
     }
 
+    fun getAllDataFiles() = dataForFiles.keys
+
     private fun isCompatible(snapshot: ClasspathSnapshot) =
         this != UnknownSnapshot
                 && snapshot != UnknownSnapshot