Commonize Char.titlecaseChar() and Char.titlecase() #KT-44369

libraries/stdlib/js/src/generated/_TitlecaseMappings.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.text
+
+//
+// NOTE: THIS FILE IS AUTO-GENERATED by the GenerateUnicodeData.kt
+// See: https://github.com/JetBrains/kotlin/tree/master/libraries/stdlib
+//
+
+// 4 ranges totally
+@OptIn(ExperimentalStdlibApi::class)
+internal fun Char.titlecaseCharImpl(): Char {
+    val code = this.toInt()
+    // Letters repeating <Lu, Lt, Ll> sequence and code of the Lt is a multiple of 3, e.g. <DŽ, Dž, dž>
+    if (code in 0x01c4..0x01cc || code in 0x01f1..0x01f3) {
+        return (3 * ((code + 1) / 3)).toChar()
+    }
+    // Lower case letters whose title case mapping equivalent is equal to the original letter
+    if (code in 0x10d0..0x10fa || code in 0x10fd..0x10ff) {
+        return this
+    }
+    return uppercaseChar()
+}

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

@@ -79,6 +79,19 @@ public actual fun Char.uppercaseChar(): Char {
 @kotlin.internal.InlineOnly
 public actual inline fun Char.uppercase(): String = toString().asDynamic().toUpperCase() as String
 
+/**
+ * Converts this character to title case using Unicode mapping rules of the invariant locale.
+ *
+ * This function performs one-to-one character mapping.
+ * To support one-to-many character mapping use the [titlecase] function.
+ * If this character has no mapping equivalent, the result of calling [uppercaseChar] is returned.
+ *
+ * @sample samples.text.Chars.titlecase
+ */
+@SinceKotlin("1.4")
+@ExperimentalStdlibApi
+public actual fun Char.titlecaseChar(): Char = titlecaseCharImpl()
+
 /**
  * Returns `true` if this character is a Unicode high-surrogate code unit (also known as leading-surrogate code unit).
  */