[K/N] String.indexOf matches byte sequences not on the char boundary #KT-56637

If the found index is odd, retry search from index + 1.

Merge-request: KT-MR-10364
Merged-by: Abduqodiri Qurbonzoda <abduqodiri.qurbonzoda@jetbrains.com>

kotlin-native/runtime/src/main/cpp/KString.cpp

@@ -398,14 +398,20 @@ KInt Kotlin_String_indexOfString(KString thiz, KString other, KInt fromIndex) {
   if (other->count_ == 0) {
     return fromIndex;
   }
-  const KChar* thizRaw = CharArrayAddressOfElementAt(thiz, fromIndex);
+  const KChar* thizRaw = CharArrayAddressOfElementAt(thiz, 0);
   const KChar* otherRaw = CharArrayAddressOfElementAt(other, 0);
-  void* result = konan::memmem(thizRaw, (thiz->count_ - fromIndex) * sizeof(KChar),
-                               otherRaw, other->count_ * sizeof(KChar));
-  if (result == nullptr) return -1;
-
-  return (reinterpret_cast<intptr_t>(result) - reinterpret_cast<intptr_t>(
-      CharArrayAddressOfElementAt(thiz, 0))) / sizeof(KChar);
+  const auto otherSize = other->count_ * sizeof(KChar);
+  while (true) {
+    void* result = konan::memmem(thizRaw + fromIndex, (thiz->count_ - fromIndex) * sizeof(KChar),
+                                 otherRaw, otherSize);
+    if (result == nullptr) return -1;
+    auto byteIndex = reinterpret_cast<intptr_t>(result) - reinterpret_cast<intptr_t>(thizRaw);
+    if (byteIndex % sizeof(KChar) == 0) {
+      return byteIndex / sizeof(KChar);
+    } else {
+      fromIndex = byteIndex / sizeof(KChar) + 1;
+    }
+  }
 }
 
 KInt Kotlin_String_lastIndexOfString(KString thiz, KString other, KInt fromIndex) {

libraries/stdlib/test/text/StringTest.kt

@@ -1856,4 +1856,17 @@ ${"    "}
         assertTrue(null.contentEquals(null, ignoreCase = true))
         assertTrue(null.contentEquals(null, ignoreCase = false))
     }
+
+    @Test
+    fun indexOfRespectsCharBoundary() {
+        withOneCharSequenceArg("\u003a\u3b3c\u003d") { input ->
+            assertEquals(-1, input.indexOf("\u3c00"))
+            assertEquals(-1, input.indexOf("\u3d3b"))
+            assertEquals(-1, input.indexOf("\u3c00\u3d3b"))
+        }
+
+        // KT-56637
+        assertEquals("買っ", "買っ".replace("掌", "X"))
+        assertEquals("買", "買".replace("掌", "X"))
+    }
 }