Lift assignment out: do not suggest if other assignments available

So #KT-18709 Fixed

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

@@ -20,6 +20,7 @@ import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.intentions.branches
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.psiUtil.anyDescendantOfType
 import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.lastBlockStatementOrThis
 import org.jetbrains.kotlin.types.typeUtil.isNothing
@@ -51,7 +52,8 @@ object BranchedFoldingUtils {
             a1.left?.text == a2.left?.text && a1.operationToken == a2.operationToken
 
     internal fun getFoldableAssignmentNumber(expression: KtExpression?): Int {
-        val assignments = mutableListOf<KtBinaryExpression>()
+        expression ?: return -1
+        val assignments = linkedSetOf<KtBinaryExpression>()
         fun collectAssignmentsAndCheck(e: KtExpression?): Boolean = when (e) {
             is KtWhenExpression -> {
                 val entries = e.entries
@@ -79,9 +81,17 @@ object BranchedFoldingUtils {
             else -> false
         }
         if (!collectAssignmentsAndCheck(expression)) return -1
-        if (assignments.isEmpty()) return 0
+        val firstAssignment = assignments.firstOrNull()
-        val firstAssignment = assignments.first()
+        if (firstAssignment != null && assignments.any { !BranchedFoldingUtils.checkAssignmentsMatch(it, firstAssignment) }) {
-        if (assignments.any { !BranchedFoldingUtils.checkAssignmentsMatch(it, firstAssignment) }) return -1
+            return -1
+        }
+        if (expression.anyDescendantOfType<KtBinaryExpression>(
+                predicate = {
+                    it.operationToken in KtTokens.ALL_ASSIGNMENTS && it !in assignments
+                }
+        )) {
+            return -1
+        }
         return assignments.size
     }
 

idea/testData/inspectionsLocal/liftOut/ifToAssignment/multipleAssignments.kt

@@ -0,0 +1,12 @@
+// PROBLEM: none
+
+fun foo(x: Boolean): String {
+    var s = ""
+    <caret>if (x) {
+        s += "a"
+        s += "b"
+    } else {
+        s += "c"
+    }
+    return s
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -442,6 +442,12 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("multipleAssignments.kt")
+            public void testMultipleAssignments() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/liftOut/ifToAssignment/multipleAssignments.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("simpleIf.kt")
             public void testSimpleIf() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/liftOut/ifToAssignment/simpleIf.kt");