WASM: Implement string hashcode

compiler/testData/codegen/box/primitiveTypes/stringEqualsHashCodeToString.kt

@@ -1,5 +1,3 @@
-// DONT_TARGET_EXACT_BACKEND: WASM
-// WASM_MUTE_REASON: String.hashCode()
 // IGNORE_BACKEND: NATIVE
 
 fun test(s: String) {

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/wasm/semantics/IrCodegenBoxWasmTestGenerated.java

@@ -11728,6 +11728,11 @@ public class IrCodegenBoxWasmTestGenerated extends AbstractIrCodegenBoxWasmTest
             runTest("compiler/testData/codegen/box/primitiveTypes/rangeTo.kt");
         }
 
+        @TestMetadata("stringEqualsHashCodeToString.kt")
+        public void testStringEqualsHashCodeToString() throws Exception {
+            runTest("compiler/testData/codegen/box/primitiveTypes/stringEqualsHashCodeToString.kt");
+        }
+
         @TestMetadata("unboxComparable.kt")
         public void testUnboxComparable() throws Exception {
             runTest("compiler/testData/codegen/box/primitiveTypes/unboxComparable.kt");

libraries/stdlib/wasm/builtins/kotlin/String.kt

@@ -56,8 +56,16 @@ public class String internal constructor(internal val chars: CharArray) : Compar
 
     public override fun toString(): String = this
 
-    // TODO: this is not nice
+    private var cachedHash: Int = 0
-    public override fun hashCode(): Int = 10
+    public override fun hashCode(): Int {
+        if (cachedHash != 0 || this.isEmpty())
+            return cachedHash
+        var hash = 0
+        for (c in chars)
+            hash = 31 * hash + c.toInt()
+        cachedHash = hash
+        return cachedHash
+    }
 }
 
 internal fun stringLiteral(startAddr: Int, length: Int) = String(unsafeRawMemoryToCharArray(startAddr, length))