JVM: Always invoke get()/charAt() in optimized for-loop over

CharSequence.withIndex(), even if element variable is unused in
destructuring declaration.

#KT-34779 Fixed

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInCharSequenceWithIndexCheckSideEffects.kt

@@ -0,0 +1,30 @@
+// KJS_WITH_FULL_RUNTIME
+// WITH_RUNTIME
+
+class CountingString(private val s: String) : CharSequence {
+    var lengthCtr = 0
+    var getCtr = 0
+
+    override val length: Int
+        get() = s.length.also { lengthCtr++ }
+
+    override fun subSequence(startIndex: Int, endIndex: Int) = TODO()
+    override fun get(index: Int) = s.get(index).also { getCtr++ }
+}
+
+val cs = CountingString("abcd")
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((index, x) in cs.withIndex()) {
+        s.append("$index:$x;")
+    }
+
+    val ss = s.toString()
+    if (ss != "0:a;1:b;2:c;3:d;") return "fail: '$ss'"
+    if (cs.lengthCtr != 5) return "lengthCtr != 5, was: '${cs.lengthCtr}'"
+    if (cs.getCtr != 4) return "getCtr != 4, was: '${cs.getCtr}'"
+
+    return "OK"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInCharSequenceWithIndexNoElementVarCheckSideEffects.kt

@@ -0,0 +1,30 @@
+// KJS_WITH_FULL_RUNTIME
+// WITH_RUNTIME
+
+class CountingString(private val s: String) : CharSequence {
+    var lengthCtr = 0
+    var getCtr = 0
+
+    override val length: Int
+        get() = s.length.also { lengthCtr++ }
+
+    override fun subSequence(startIndex: Int, endIndex: Int) = TODO()
+    override fun get(index: Int) = s.get(index).also { getCtr++ }
+}
+
+val cs = CountingString("abcd")
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((index, _) in cs.withIndex()) {
+        s.append("$index;")
+    }
+
+    val ss = s.toString()
+    if (ss != "0;1;2;3;") return "fail: '$ss'"
+    if (cs.lengthCtr != 5) return "lengthCtr != 5, was: '${cs.lengthCtr}'"
+    if (cs.getCtr != 4) return "getCtr != 4, was: '${cs.getCtr}'"
+
+    return "OK"
+}

compiler/testData/codegen/box/controlStructures/forInCharSequenceWithIndex/forInCharSequenceWithIndexNoIndexVarCheckSideEffects.kt

@@ -0,0 +1,29 @@
+// KJS_WITH_FULL_RUNTIME
+// WITH_RUNTIME
+
+class CountingString(private val s: String) : CharSequence {
+    var lengthCtr = 0
+    var getCtr = 0
+
+    override val length: Int
+        get() = s.length.also { lengthCtr++ }
+
+    override fun subSequence(startIndex: Int, endIndex: Int) = TODO()
+    override fun get(index: Int) = s.get(index).also { getCtr++ }
+}
+val cs = CountingString("abcd")
+
+fun box(): String {
+    val s = StringBuilder()
+
+    for ((_, x) in cs.withIndex()) {
+        s.append("$x;")
+    }
+
+    val ss = s.toString()
+    if (ss != "a;b;c;d;") return "fail: '$ss'"
+    if (cs.lengthCtr != 5) return "lengthCtr != 5, was: '${cs.lengthCtr}'"
+    if (cs.getCtr != 4) return "getCtr != 4, was: '${cs.getCtr}'"
+
+    return "OK"
+}