FirForLoopChecker: report also OPERATOR_MODIFIER if appropriate + minor

This commits checks iterator/hasNext/next functions whether they are
declared as operator or not. Also, it changes logic of hasNext/next
error reporting, now we're able to report errors about both these
functions.

compiler/testData/diagnostics/tests/ForRangeConventions.fir.kt

@@ -79,7 +79,7 @@ abstract class NotRange8() {
 
 fun test(notRange1: NotRange1, notRange2: NotRange2, notRange3: NotRange3, notRange4: NotRange4, notRange5: NotRange5, notRange6: NotRange6, notRange7: NotRange7, notRange8: NotRange8, range0: Range0, range1: Range1) {
   for (i in <!ITERATOR_MISSING!>notRange1<!>);
-  for (i in <!HAS_NEXT_MISSING!>notRange2<!>);
+  for (i in <!HAS_NEXT_MISSING, NEXT_MISSING!>notRange2<!>);
   for (i in <!NEXT_MISSING!>notRange3<!>);
   for (i in <!HAS_NEXT_MISSING!>notRange4<!>);
   for (i in notRange5);

compiler/testData/diagnostics/tests/Operators.fir.kt

@@ -111,4 +111,31 @@ fun test2() {
     Anc() + Anc()
     Anc() - Anc()
     Anc2() + Anc2()
-}
+}
+
+fun Int.iterator(): MyIntIterator = null!!
+
+operator fun Double.iterator(): MyDoubleIterator = null!!
+
+operator fun Boolean.iterator(): MyBooleanIterator = null!!
+
+interface MyIntIterator {
+    operator fun hasNext(): Boolean
+    operator fun next(): Int
+}
+
+interface MyDoubleIterator {
+    operator fun hasNext(): Boolean
+    fun next(): Double
+}
+
+interface MyBooleanIterator {
+    fun hasNext(): Boolean
+    operator fun next(): Boolean
+}
+
+fun test3(i: Int, d: Double, b: Boolean) {
+    for (element in <!OPERATOR_MODIFIER_REQUIRED!>i<!>) {}
+    for (element in <!OPERATOR_MODIFIER_REQUIRED!>d<!>) {}
+    for (element in <!OPERATOR_MODIFIER_REQUIRED!>b<!>) {}
+}

compiler/testData/diagnostics/tests/Operators.kt

@@ -111,4 +111,31 @@ fun test2() {
     Anc() + Anc()
     Anc() <!OPERATOR_MODIFIER_REQUIRED!>-<!> Anc()
     Anc2() + Anc2()
-}
+}
+
+fun Int.iterator(): MyIntIterator = null!!
+
+operator fun Double.iterator(): MyDoubleIterator = null!!
+
+operator fun Boolean.iterator(): MyBooleanIterator = null!!
+
+interface MyIntIterator {
+    operator fun hasNext(): Boolean
+    operator fun next(): Int
+}
+
+interface MyDoubleIterator {
+    operator fun hasNext(): Boolean
+    fun next(): Double
+}
+
+interface MyBooleanIterator {
+    fun hasNext(): Boolean
+    operator fun next(): Boolean
+}
+
+fun test3(i: Int, d: Double, b: Boolean) {
+    for (element in <!OPERATOR_MODIFIER_REQUIRED!>i<!>) {}
+    for (element in <!OPERATOR_MODIFIER_REQUIRED!>d<!>) {}
+    for (element in <!OPERATOR_MODIFIER_REQUIRED!>b<!>) {}
+}

compiler/testData/diagnostics/tests/Operators.txt

@@ -2,6 +2,10 @@ package
 
 public fun test(): kotlin.Unit
 public fun test2(): kotlin.Unit
+public fun test3(/*0*/ i: kotlin.Int, /*1*/ d: kotlin.Double, /*2*/ b: kotlin.Boolean): kotlin.Unit
+public operator fun kotlin.Boolean.iterator(): MyBooleanIterator
+public operator fun kotlin.Double.iterator(): MyDoubleIterator
+public fun kotlin.Int.iterator(): MyIntIterator
 
 public open class Anc : Base {
     public constructor Anc()
@@ -65,3 +69,28 @@ public final class Example2 {
     public final operator fun rangeTo(/*0*/ o: Example2): Example2
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
+
+public interface MyBooleanIterator {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun hasNext(): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public abstract operator fun next(): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface MyDoubleIterator {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract operator fun hasNext(): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public abstract fun next(): kotlin.Double
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface MyIntIterator {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract operator fun hasNext(): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public abstract operator fun next(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+

compiler/testData/diagnostics/tests/controlStructures/forWithNullableIterator.fir.kt

@@ -1,12 +0,0 @@
-class Coll {
-  operator fun iterator(): It? = null
-}
-
-class It {
-  operator fun next() = 1
-  operator fun hasNext() = false
-}
-
-fun test() {
-  for (x in <!HAS_NEXT_FUNCTION_NONE_APPLICABLE!>Coll()<!>) {}
-}

compiler/testData/diagnostics/tests/controlStructures/forWithNullableIterator.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 class Coll {
   operator fun iterator(): It? = null
 }

compiler/testData/diagnostics/tests/inference/reportingImprovements/typeInferenceFailedOnIteratorCall.fir.kt

@@ -4,6 +4,6 @@ class X
 operator fun <T> X.iterator(): Iterable<T> = TODO()
 
 fun test() {
-    for (i in <!HAS_NEXT_MISSING!>X()<!>) {
+    for (i in <!HAS_NEXT_MISSING, NEXT_MISSING!>X()<!>) {
     }
 }