Warn on for-in-array range variable assignment in loop body

According to KT-21354, this should be a warning in 1.2 and before, and
no warning (with changed semantics) in 1.3 and later.
NB there are some false positives in this check.

 #KT-21354 In Progress
 #KT-21321 In Progress

compiler/testData/diagnostics/testsWithStdLib/forInArrayLoop/capturedRangeVariableAssignmentBefore13.kt

@@ -0,0 +1,103 @@
+// !LANGUAGE: -ProperForInArrayLoopRangeVariableAssignmentSemantic
+// !DIAGNOSTICS: -UNUSED_VALUE
+// SKIP_TXT
+
+fun testArrayCapturedInLocalFun() {
+    var xs = arrayOf("a", "b", "c")
+
+    fun updateXs() {
+        xs = arrayOf("d", "e", "f")
+    }
+
+    for (x in xs) {
+        println(x)
+        updateXs()
+    }
+}
+
+fun testArrayCapturedInLabmda() {
+    var xs = arrayOf("a", "b", "c")
+
+    val updateXs = { xs = arrayOf("d", "e", "f") }
+
+    for (x in xs) {
+        println(x)
+        updateXs()
+    }
+}
+
+fun testArrayCapturedInInlineLambda() {
+    var xs = arrayOf("a", "b", "c")
+
+    for (x in xs) {
+        println(x)
+        run {
+            xs = arrayOf("d", "e", "f")
+        }
+    }
+}
+
+fun testArrayCapturedInLocalObject() {
+    var xs = arrayOf("a", "b", "c")
+
+    val updateXs = object : () -> Unit {
+        override fun invoke() {
+            xs = arrayOf("d", "e", "f")
+        }
+    }
+
+    for (x in xs) {
+        println(x)
+        updateXs()
+    }
+}
+
+fun testArrayCapturedInLocalClass() {
+    var xs = arrayOf("a", "b", "c")
+
+    class LocalClass {
+        fun updateXs() {
+            xs = arrayOf("d", "e", "f")
+        }
+    }
+
+    val updater = LocalClass()
+
+    for (x in xs) {
+        println(x)
+        updater.updateXs()
+    }
+}
+
+fun testCapturedInLambdaAfterLoop() {
+    // NB false positive
+    var xs = intArrayOf(1, 2, 3)
+    for (x in xs) {
+        println(x)
+        <!ASSIGNMENT_TO_ARRAY_LOOP_VARIABLE!>xs<!> = intArrayOf(4, 5, 6)
+    }
+    val lambda = { xs = intArrayOf() }
+    lambda()
+}
+
+fun testCapturedInLambdaInLoopAfterAssignment() {
+    // NB false positive
+    var xs = intArrayOf(1, 2, 3)
+    for (x in xs) {
+        println(x)
+        <!ASSIGNMENT_TO_ARRAY_LOOP_VARIABLE!>xs<!> = intArrayOf(4, 5, 6)
+        val lambda = { xs = intArrayOf() }
+        lambda()
+    }
+}
+
+fun testCapturedInNonChangingClosure() {
+    // NB false positive
+    var xs = intArrayOf(1, 2, 3)
+    val lambda = { println(xs) }
+    for (x in xs) {
+        println(x)
+        <!ASSIGNMENT_TO_ARRAY_LOOP_VARIABLE!>xs<!> = intArrayOf(4, 5, 6)
+        lambda()
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/forInArrayLoop/rangeLocalDelegatedPropertyAssignmentBefore13.kt

@@ -0,0 +1,16 @@
+// !LANGUAGE: -ProperForInArrayLoopRangeVariableAssignmentSemantic
+// !DIAGNOSTICS: -UNUSED_VALUE
+// SKIP_TXT
+
+class Delegate<T>(var v: T) {
+    operator fun getValue(thisRef: Any?, kProp: Any?) = v
+    operator fun setValue(thisRef: Any?, kProp: Any?, value: T) { v = value }
+}
+
+fun testLocalDelegatedProperty() {
+    var xs by Delegate(arrayOf("a", "b", "c"))
+    for (x in xs) {
+        println(x)
+        xs = arrayOf("d", "e", "f")
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/forInArrayLoop/rangeVariableAssignment13.kt

@@ -0,0 +1,19 @@
+// !LANGUAGE: +ProperForInArrayLoopRangeVariableAssignmentSemantic
+// !DIAGNOSTICS: -UNUSED_VALUE
+// SKIP_TXT
+
+fun testObjectArray() {
+    var xs = arrayOf("a", "b", "c")
+    for (x in xs) {
+        println(x)
+        xs = arrayOf("d", "e", "f")
+    }
+}
+
+fun testPrimitiveArray() {
+    var xs = intArrayOf(1, 2, 3)
+    for (x in xs) {
+        println(x)
+        xs = intArrayOf(4, 5, 6)
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/forInArrayLoop/rangeVariableAssignmentBefore13.kt

@@ -0,0 +1,39 @@
+// !LANGUAGE: -ProperForInArrayLoopRangeVariableAssignmentSemantic
+// !DIAGNOSTICS: -UNUSED_VALUE
+// SKIP_TXT
+
+fun testObjectArray() {
+    var xs = arrayOf("a", "b", "c")
+    for (x in xs) {
+        println(x)
+        <!ASSIGNMENT_TO_ARRAY_LOOP_VARIABLE!>xs<!> = arrayOf("d", "e", "f")
+    }
+}
+
+fun testPrimitiveArray() {
+    var xs = intArrayOf(1, 2, 3)
+    for (x in xs) {
+        println(x)
+        <!ASSIGNMENT_TO_ARRAY_LOOP_VARIABLE!>xs<!> = intArrayOf(4, 5, 6)
+    }
+}
+
+var global = arrayOf("a", "b", "c")
+
+fun testGlobalArray() {
+    for (x in global) {
+        println(x)
+        global = arrayOf("d", "e", "f")
+    }
+}
+
+fun testAssignmentNotInLoop() {
+    var xs = intArrayOf(1, 2, 3)
+    println(xs)
+    xs = intArrayOf(7, 8, 9)
+    for (x in xs) {
+        println(x)
+    }
+    xs = intArrayOf(4, 5, 6)
+    println(xs)
+}