Lift assignment out: do not highlight for exactly one assignment

Related to KT-14900

idea/src/org/jetbrains/kotlin/idea/inspections/LiftReturnOrAssignmentInspection.kt

@@ -42,11 +42,13 @@ class LiftReturnOrAssignmentInspection : AbstractKotlinInspection() {
                         )
                         return
                     }
-                    if (BranchedFoldingUtils.canFoldToAssignment(expression)) {
+                    val assignmentNumber = BranchedFoldingUtils.getFoldableAssignmentNumber(expression)
+                    if (assignmentNumber > 0) {
                         holder.registerProblem(
                                 keyword,
                                 "Assignment can be lifted out of '${keyword.text}'",
-                                ProblemHighlightType.GENERIC_ERROR_OR_WARNING,
+                                if (assignmentNumber > 1) ProblemHighlightType.GENERIC_ERROR_OR_WARNING
+                                else ProblemHighlightType.INFORMATION,
                                 LiftAssignmentOutFix(keyword.text)
                         )
                     }

idea/src/org/jetbrains/kotlin/idea/intentions/branchedTransformations/BranchedFoldingUtils.kt

@@ -48,7 +48,7 @@ object BranchedFoldingUtils {
     fun checkAssignmentsMatch(a1: KtBinaryExpression, a2: KtBinaryExpression): Boolean =
             a1.left?.text == a2.left?.text && a1.operationToken == a2.operationToken
 
-    fun canFoldToAssignment(expression: KtExpression?): Boolean {
+    internal fun getFoldableAssignmentNumber(expression: KtExpression?): Int {
         val assignments = mutableListOf<KtBinaryExpression>()
         fun collectAssignmentsAndCheck(e: KtExpression?): Boolean = when (e) {
             is KtWhenExpression -> {
@@ -76,10 +76,11 @@ object BranchedFoldingUtils {
             is KtThrowExpression, is KtReturnExpression -> true
             else -> false
         }
-        if (!collectAssignmentsAndCheck(expression)) return false
-        if (assignments.isEmpty()) return false
+        if (!collectAssignmentsAndCheck(expression)) return -1
+        if (assignments.isEmpty()) return 0
         val firstAssignment = assignments.first()
-        return assignments.all { BranchedFoldingUtils.checkAssignmentsMatch(it, firstAssignment) }
+        if (assignments.any { !BranchedFoldingUtils.checkAssignmentsMatch(it, firstAssignment) }) return -1
+        return assignments.size
     }
 
     private fun getFoldableReturnNumber(branches: List<KtExpression?>) =

idea/testData/inspectionsLocal/liftOut/whenToAssignment/insideLoop.kt

@@ -1,3 +1,5 @@
+// HIGHLIGHT: INFORMATION
+
 fun foo(): Int {
     var res = 0
     loop@ while (true) {

idea/testData/inspectionsLocal/liftOut/whenToAssignment/insideLoop.kt.after

@@ -1,3 +1,5 @@
+// HIGHLIGHT: INFORMATION
+
 fun foo(): Int {
     var res = 0
     loop@ while (true) {

idea/testData/inspectionsLocal/liftOut/whenToAssignment/simpleWhen.kt

@@ -1,3 +1,5 @@
+// HIGHLIGHT: GENERIC_ERROR_OR_WARNING
+
 fun test(n: Int): String {
     var res: String
 

idea/testData/inspectionsLocal/liftOut/whenToAssignment/simpleWhen.kt.after

@@ -1,3 +1,5 @@
+// HIGHLIGHT: GENERIC_ERROR_OR_WARNING
+
 fun test(n: Int): String {
     var res: String