ScriptTemplatesClassRootsIndex: inc version and minor fixes

Content was changed, so we should force reindex.

Minor changes:
- There is no need to save a string, we can just save nothing
 by using the Unit value (see UnitKey.save and UnitKey.read)
- Unit can be shared between all indexes, so we can extract UnitKey object
- It would be good to extract abstract class FileListIndex:
  - for better readability: separate the logic of the specific index from the common FileListIndex implementation
  - someone can use it also
- mapOf (Unit to null) will create singletonMap itself and more readable
- ScriptTemplatesClassRootsIndex.KEY perhaps better to call NAME

idea/scripting-support/test/org/jetbrains/kotlin/idea/script/AbstractScriptTemplatesFromDependenciesTest.kt

@@ -78,8 +78,8 @@ abstract class AbstractScriptTemplatesFromDependenciesTest : HeavyPlatformTestCa
         }
 
         val roots: Collection<VirtualFile> = FileBasedIndex.getInstance().getContainingFiles(
-            ScriptTemplatesClassRootsIndex.KEY,
-            ScriptTemplatesClassRootsIndex.VALUE,
+            ScriptTemplatesClassRootsIndex.NAME,
+            Unit,
             GlobalSearchScope.allScope(project)
         )
 

idea/src/org/jetbrains/kotlin/idea/script/ScriptTemplatesClassRootsIndex.kt

@@ -13,33 +13,38 @@ import org.jetbrains.kotlin.scripting.definitions.SCRIPT_DEFINITION_MARKERS_EXTE
 import org.jetbrains.kotlin.scripting.definitions.SCRIPT_DEFINITION_MARKERS_PATH
 import java.io.DataInput
 import java.io.DataOutput
-import java.util.*
+
+object UnitKey : KeyDescriptor<Unit> {
+    override fun getHashCode(value: Unit) = 0
+    override fun isEqual(val1: Unit, val2: Unit) = true
+    override fun save(out: DataOutput, value: Unit?) = Unit
+    override fun read(`in`: DataInput) = Unit
+}
+
+abstract class FileListIndex :
+    ScalarIndexExtension<Unit>(),
+    DataIndexer<Unit, Void, FileContent> {
+
+    override fun getIndexer() = this
+    override fun getKeyDescriptor() = UnitKey
+    override fun dependsOnFileContent() = false
+    override fun map(inputData: FileContent) = mapOf(Unit to null)
+}
 
 class ScriptTemplatesClassRootsIndex :
-    ScalarIndexExtension<String>(),
-    FileBasedIndex.InputFilter, KeyDescriptor<String>,
-    DataIndexer<String, Void, FileContent> {
+    FileListIndex(),
+    FileBasedIndex.InputFilter {
 
     companion object {
-        val KEY = ID.create<String, Void>(ScriptTemplatesClassRootsIndex::class.java.canonicalName)
+        val NAME = ID.create<Unit, Void>(ScriptTemplatesClassRootsIndex::class.java.canonicalName)
         const val VALUE = "MY_VALUE"
-
         private val suffix = SCRIPT_DEFINITION_MARKERS_PATH.removeSuffix("/")
     }
 
-    override fun getName(): ID<String, Void> = KEY
-
-    override fun getIndexer(): DataIndexer<String, Void, FileContent> = this
-
-    override fun getKeyDescriptor(): KeyDescriptor<String> = this
-
-    override fun getInputFilter(): FileBasedIndex.InputFilter = this
-
-    override fun dependsOnFileContent() = false
-
-    override fun getVersion(): Int = 2
-
+    override fun getName() = NAME
+    override fun getVersion(): Int = 3
     override fun indexDirectories(): Boolean = false
+    override fun getInputFilter(): FileBasedIndex.InputFilter = this
 
     override fun acceptInput(file: VirtualFile): Boolean {
         val parent = file.parent ?: return false
@@ -47,18 +52,4 @@ class ScriptTemplatesClassRootsIndex :
                 && parent.path.endsWith(suffix)
                 && file.path.endsWith(SCRIPT_DEFINITION_MARKERS_EXTENSION_WITH_DOT)
     }
-
-    override fun save(out: DataOutput, value: String) = IOUtil.writeUTF(out, value)
-
-    override fun read(input: DataInput): String? = IOUtil.readUTF(input)
-
-    override fun getHashCode(value: String): Int = value.hashCode()
-
-    override fun isEqual(val1: String?, val2: String?): Boolean {
-        return val1 == val2
-    }
-
-    override fun map(inputData: FileContent): Map<String?, Void?> {
-        return Collections.singletonMap(VALUE, null)
-    }
 }

idea/src/org/jetbrains/kotlin/idea/script/ScriptTemplatesFromDependenciesProvider.kt

@@ -106,8 +106,8 @@ class ScriptTemplatesFromDependenciesProvider(private val project: Project) : Sc
         ReadAction
             .nonBlocking<List<VirtualFile>> {
                 FileBasedIndex.getInstance().getContainingFiles(
-                    ScriptTemplatesClassRootsIndex.KEY,
-                    ScriptTemplatesClassRootsIndex.VALUE,
+                    ScriptTemplatesClassRootsIndex.NAME,
+                    Unit,
                     GlobalSearchScope.allScope(project)
                 ).filterNotNull()
             }