KT-45777: Ignore Kotlin synthetic classes when computing classpath changes

compiler/incremental-compilation-impl/src/org/jetbrains/kotlin/incremental/classpathDiff/BasicClassInfo.kt

@@ -28,18 +28,14 @@ class BasicClassInfo(
     val isPrivate = flagEnabled(accessFlags, Opcodes.ACC_PRIVATE)
     val isLocal = classId.isLocal
 
-    /** Whether this is a synthetic Java class. */
-    val isJavaSynthetic = !isKotlinClass && flagEnabled(accessFlags, Opcodes.ACC_SYNTHETIC)
-
-    /**
-     * Whether this is a synthetic Kotlin class.
-     *
-     * Note that we use [KotlinClassHeader.Kind], not [accessFlags], to make this determination. For example,
-     * 'kotlin/Metadata.DefaultImpls' is synthetic according to its [KotlinClassHeader.Kind], but not synthetic according to its
-     * [accessFlags].
-     */
-    @Suppress("unused")
-    val isKotlinSynthetic = isKotlinClass && kotlinClassHeader!!.kind == KotlinClassHeader.Kind.SYNTHETIC_CLASS
+    val isSynthetic = if (isKotlinClass) {
+        // Note that this property is `true` if one of the two checks below is `true`.
+        // For example, `kotlin/Metadata.DefaultImpls` is synthetic according to its [KotlinClassHeader.Kind], but not synthetic according
+        // to its [accessFlags]. (It's unclear if there is an opposite example.)
+        (kotlinClassHeader!!.kind == KotlinClassHeader.Kind.SYNTHETIC_CLASS) || flagEnabled(accessFlags, Opcodes.ACC_SYNTHETIC)
+    } else {
+        flagEnabled(accessFlags, Opcodes.ACC_SYNTHETIC)
+    }
 
     private fun flagEnabled(accessFlags: Int, flagToCheck: Int) = (accessFlags and flagToCheck) != 0
 

compiler/incremental-compilation-impl/src/org/jetbrains/kotlin/incremental/classpathDiff/ClasspathSnapshotter.kt

@@ -186,15 +186,15 @@ object ClassSnapshotter {
      */
     private fun getInaccessibleClasses(classesInfo: List<BasicClassInfo>): List<BasicClassInfo> {
         fun BasicClassInfo.isInaccessible(): Boolean {
-            if (this.isKotlinClass && this.kotlinClassHeader!!.kind != KotlinClassHeader.Kind.CLASS) {
-                // We're not sure about these kinds of Kotlin classes, so we assume it's accessible (see this method's kdoc)
-                return false
-            }
-            return if (isKotlinClass) {
-                // TODO: Is it safe to add isKotlinSynthetic to this lists?
-                isPrivate || isLocal || isAnonymous
+            return if (this.isKotlinClass) {
+                when (this.kotlinClassHeader!!.kind) {
+                    KotlinClassHeader.Kind.CLASS -> isPrivate || isLocal || isAnonymous || isSynthetic
+                    KotlinClassHeader.Kind.SYNTHETIC_CLASS -> true
+                    // We're not sure about the other kinds of Kotlin classes, so we assume it's accessible (see this method's kdoc)
+                    else -> false
+                }
             } else {
-                isPrivate || isLocal || isAnonymous || isJavaSynthetic
+                isPrivate || isLocal || isAnonymous || isSynthetic
             }
         }