JS backend: move StringBuilder to java.lang. Fix append return type.

idea/testData/completion/basic/common/ExtensionForProperty.kt

@@ -5,7 +5,7 @@ class Test {
 // INVOCATION_COUNT: 1
 // EXIST: String~(jet)
 // EXIST: IllegalStateException
-// EXIST_JAVA_ONLY: StringBuilder
+// EXIST: StringBuilder
 // EXIST_JAVA_ONLY: StringBuffer
 // ABSENT: HTMLStyleElement
 // ABSENT: Statement@Statement~(java.sql)

idea/testData/completion/basic/common/ExtensionInsideFunction.kt

@@ -17,6 +17,6 @@ class StrMore {
 // EXIST: StrSome
 // EXIST: StrMore
 // EXIST: StrInFun
-// EXIST_JAVA_ONLY: StringBuilder
+// EXIST: StringBuilder
 // EXIST_JAVA_ONLY: StringBuffer
 // ABSENT: StrAbsent

idea/testData/completion/basic/common/InParametersTypes.kt

@@ -8,7 +8,7 @@ class SomeClass {
 // EXIST: SomeClass, SomeInternal
 // EXIST: String~(jet)
 // EXIST: IllegalStateException
-// EXIST_JAVA_ONLY: StringBuilder
+// EXIST: StringBuilder
 // EXIST_JAVA_ONLY: StringBuffer
 // ABSENT: HTMLStyleElement
 // ABSENT: Statement@Statement~(java.sql)

js/js.libraries/src/core/javalang.kt

@@ -39,7 +39,17 @@ public trait Comparable<T> {
 
 library
 public trait Appendable {
-    public open fun append(csq: CharSequence?): Appendable?
-    public open fun append(csq: CharSequence?, start: Int, end: Int): Appendable?
-    public open fun append(c: Char): Appendable?
+    public open fun append(csq: CharSequence?): Appendable
+    //public open fun append(csq: CharSequence?, start: Int, end: Int): Appendable
+    public open fun append(c: Char): Appendable
+}
+
+library
+public class StringBuilder() : Appendable {
+    override fun append(c: Char): StringBuilder = js.noImpl
+    override fun append(csq: CharSequence?): StringBuilder = js.noImpl
+    //TODO
+    //override fun append(csq: CharSequence?, start: Int, end: Int): StringBuilder = js.noImpl
+    public fun append(obj: Any?): StringBuilder = js.noImpl
+    public fun toString(): String = js.noImpl
 }

js/js.libraries/src/core/javautil.kt

@@ -103,15 +103,6 @@ public open class HashMap<K, V>(capacity: Int = 0) : MutableMap<K, V> {
     public override fun entrySet(): MutableSet<MutableMap.MutableEntry<K, V>> = js.noImpl
 }
 
-library
-public class StringBuilder() : Appendable {
-    override fun append(c: Char): Appendable? = js.noImpl
-    override fun append(csq: CharSequence?): Appendable? = js.noImpl
-    override fun append(csq: CharSequence?, start: Int, end: Int): Appendable? = js.noImpl
-    public fun append(obj: Any?): StringBuilder = js.noImpl
-    public fun toString(): String = js.noImpl
-}
-
 library
 public class NoSuchElementException() : Exception() {
 }

js/js.translator/testFiles/standardClasses/cases/stringBuilder.kt

@@ -1,12 +1,11 @@
 package foo
 
-import java.util.StringBuilder
 
 fun box(): String {
     val s = StringBuilder()
     s.append("a")
-    s.append("b")?.append("c")
-    s.append("d")!!.append("e")
+    s.append("b").append("c")
+    s.append('d').append("e")
 
     if (s.toString() != "abcde") return s.toString()
     return "OK"