Fix String.dropWhile & String.takeWhile

libraries/stdlib/src/generated/_Filtering.kt

@@ -354,7 +354,7 @@ public fun <T> Stream<T>.dropWhile(predicate: (T) -> Boolean): Stream<T> {
  * Returns a list containing all elements except first elements that satisfy the given *predicate*
  */
 public inline fun String.dropWhile(predicate: (Char) -> Boolean): String {
-    for (index in 0..length)
+    for (index in 0..length - 1)
         if (!predicate(get(index))) {
             return substring(index)
         }
@@ -1240,10 +1240,10 @@ public fun <T> Stream<T>.takeWhile(predicate: (T) -> Boolean): Stream<T> {
  * Returns a list containing first elements satisfying the given *predicate*
  */
 public inline fun String.takeWhile(predicate: (Char) -> Boolean): String {
-    for (index in 0..length)
+    for (index in 0..length - 1)
         if (!predicate(get(index))) {
             return substring(0, index)
         }
-    return ""
+    return this
 }
 

libraries/stdlib/test/text/StringJVMTest.kt

@@ -240,8 +240,9 @@ class StringJVMTest {
 
     test fun dropWhile() {
         val data = "ab1cd2"
-        val result = data.dropWhile { it.isJavaLetter() }
+        assertEquals("1cd2", data.dropWhile { it.isJavaLetter() })
-        assertEquals("1cd2", result)
+        assertEquals("", data.dropWhile { true })
+        assertEquals("ab1cd2", data.dropWhile { false })
     }
 
     test fun drop() {
@@ -255,8 +256,9 @@ class StringJVMTest {
 
     test fun takeWhile() {
         val data = "ab1cd2"
-        val result = data.takeWhile { it.isJavaLetter() }
+        assertEquals("ab", data.takeWhile { it.isJavaLetter() })
-        assertEquals("ab", result)
+        assertEquals("", data.takeWhile { false })
+        assertEquals("ab1cd2", data.takeWhile { true })
     }
 
     test fun take() {

libraries/tools/kotlin-stdlib-gen/src/templates/Filtering.kt

@@ -113,7 +113,7 @@ fun filtering(): List<GenericFunction> {
         returns(Strings) { "String" }
         body(Strings) {
             """
-            for (index in 0..length)
+            for (index in 0..length - 1)
                 if (!predicate(get(index))) {
                     return substring(index)
                 }
@@ -161,11 +161,11 @@ fun filtering(): List<GenericFunction> {
         returns(Strings) { "String" }
         body(Strings) {
             """
-            for (index in 0..length)
+            for (index in 0..length - 1)
                 if (!predicate(get(index))) {
                     return substring(0, index)
                 }
-            return ""
+            return this
             """
         }