Introduce StringBuilder.clear() extension

#KT-18910 Fixed

libraries/stdlib/common/src/kotlin/TextH.kt

@@ -129,6 +129,15 @@ public expect fun String.decapitalize(): String
 public expect fun CharSequence.repeat(n: Int): String
 
 
+/**
+ * Clears the content of this string builder making it empty.
+ *
+ * @sample samples.text.Strings.clearStringBuilder
+ */
+@SinceKotlin("1.3")
+public expect fun StringBuilder.clear(): StringBuilder
+
+
 /**
  * Returns a new string with all occurrences of [oldChar] replaced with [newChar].
  */

libraries/stdlib/js/src/kotlin/text.kt

@@ -53,5 +53,27 @@ public actual class StringBuilder(content: String = "") : Appendable, CharSequen
         return this
     }
 
+    /**
+     * Clears the content of this string builder making it empty.
+     *
+     * @sample samples.text.Strings.clearStringBuilder
+     */
+    @SinceKotlin("1.3")
+    public fun clear(): StringBuilder {
+        string = ""
+        return this
+    }
+
     override fun toString(): String = string
 }
+
+
+
+/**
+ * Clears the content of this string builder making it empty.
+ *
+ * @sample samples.text.Strings.clearStringBuilder
+ */
+@SinceKotlin("1.3")
+@Suppress("EXTENSION_SHADOWED_BY_MEMBER")
+public actual fun StringBuilder.clear(): StringBuilder = this.clear()

libraries/stdlib/jvm/src/kotlin/text/StringBuilderJVM.kt

@@ -14,6 +14,13 @@ package kotlin.text
 @kotlin.internal.InlineOnly
 public inline operator fun StringBuilder.set(index: Int, value: Char): Unit = this.setCharAt(index, value)
 
+/**
+ * Clears the content of this string builder making it empty.
+ *
+ * @sample samples.text.Strings.clearStringBuilder
+ */
+@SinceKotlin("1.3")
+public actual fun StringBuilder.clear(): StringBuilder = apply { setLength(0) }
 
 private object SystemProperties {
     /** Line separator for current system. */

libraries/stdlib/samples/test/samples/text/strings.kt

@@ -127,4 +127,14 @@ class Strings {
         val noPadding = "abcde".padEnd(3)
         assertPrints("'$noPadding'", "'abcde'")
     }
+    @Sample
+    fun clearStringBuilder() {
+        val builder = StringBuilder()
+        builder.append("content").append(1)
+        assertPrints(builder, "content1")
+
+        builder.clear()
+        assertPrints(builder, "")
+    }
+
 }

libraries/stdlib/test/text/StringBuilderTest.kt

@@ -66,4 +66,13 @@ class StringBuilderTest {
             assertEquals("content", sb.toString())
         }
     }
+
+    @Test fun clear() {
+        val sb = StringBuilder()
+        sb.append("test")
+        val s = sb.toString()
+        sb.clear()
+        assertTrue(sb.isEmpty())
+        assertEquals("test", s)
+    }
 }

libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib-runtime-merged.txt

@@ -4731,6 +4731,7 @@ public final class kotlin/text/StringsKt {
 	public static final fun chunked (Ljava/lang/CharSequence;ILkotlin/jvm/functions/Function1;)Ljava/util/List;
 	public static final fun chunkedSequence (Ljava/lang/CharSequence;I)Lkotlin/sequences/Sequence;
 	public static final fun chunkedSequence (Ljava/lang/CharSequence;ILkotlin/jvm/functions/Function1;)Lkotlin/sequences/Sequence;
+	public static final fun clear (Ljava/lang/StringBuilder;)Ljava/lang/StringBuilder;
 	public static final fun commonPrefixWith (Ljava/lang/CharSequence;Ljava/lang/CharSequence;Z)Ljava/lang/String;
 	public static synthetic fun commonPrefixWith$default (Ljava/lang/CharSequence;Ljava/lang/CharSequence;ZILjava/lang/Object;)Ljava/lang/String;
 	public static final fun commonSuffixWith (Ljava/lang/CharSequence;Ljava/lang/CharSequence;Z)Ljava/lang/String;