Add script files changes monitoring, logic for initialization during index rebuilding

compiler/frontend/src/org/jetbrains/kotlin/script/KotlinScriptDefinition.kt

@@ -69,6 +69,13 @@ class KotlinScriptExternalDependenciesUnion(val dependencies: Iterable<KotlinScr
     override val sources: Iterable<File> get() = dependencies.flatMap { it.sources }
 }
 
+fun Iterable<File>.isSameClasspathAs(other: Iterable<File>): Boolean {
+    val c1 = map { it.canonicalPath }.toHashSet()
+    val c2 = other.map { it.canonicalPath }.toHashSet()
+    return c1.size == c2.size &&
+           c1.zip(c2).all { it.first == it.second }
+}
+
 data class ScriptParameter(val name: Name, val type: KotlinType)
 
 fun <TF> getFileName(file: TF): String = when (file) {

compiler/frontend/src/org/jetbrains/kotlin/script/KotlinScriptExternalImportsProvider.kt

@@ -49,6 +49,7 @@ class KotlinScriptExternalImportsProvider(val project: Project, private val scri
         }
     }
 
+    // optimized for initial caching, additional handling of possible duplicates to save a call to distinct
     fun <TF> cacheExternalImports(files: Iterable<TF>): Unit = cacheLock.write {
         val uncached = hashSetOf<String>()
         files.forEach { file ->
@@ -71,6 +72,36 @@ class KotlinScriptExternalImportsProvider(val project: Project, private val scri
         }
     }
 
+    // optimized for update, no special duplicates handling
+    fun <TF: Any> updateExternalImportsCache(files: Iterable<TF>): Iterable<TF> = cacheLock.write {
+        files.mapNotNull { file ->
+            val path = getFilePath(file)
+            val scriptDef = scriptDefinitionProvider.findScriptDefinition(file)
+            if (scriptDef != null) {
+                val deps = scriptDef.getDependenciesFor(file, project)
+                val oldDeps = cache[path]
+                when {
+                    deps != null && (oldDeps == null ||
+                                     !deps.classpath.isSameClasspathAs(oldDeps.classpath) || !deps.sources.isSameClasspathAs(oldDeps.sources)) -> {
+                        // changed or new
+                        cache.put(path, deps)
+                        cacheOfNulls.remove(path)
+                        file
+                    }
+                    deps != null -> {
+                        // same as before
+                        null
+                    }
+                    else -> {
+                        if (cache.remove(path) != null || cacheOfNulls.remove(path)) file // cleared
+                        else null // same as before
+                    }
+                }
+            }
+            else null // not a script
+        }
+    }
+
     fun invalidateCaches() {
         cacheLock.write {
             cache.keys.toList().apply {