Fixed bug in MergeWhenIntention

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

@@ -21,6 +21,7 @@ import com.intellij.openapi.util.TextRange
 import com.intellij.psi.PsiWhiteSpace
 import com.intellij.psi.util.PsiTreeUtil
 import org.jetbrains.kotlin.idea.intentions.JetSelfTargetingRangeIntention
+import org.jetbrains.kotlin.idea.intentions.branchedTransformations.isStableVariable
 import org.jetbrains.kotlin.idea.util.psi.patternMatching.matches
 import org.jetbrains.kotlin.idea.util.psi.patternMatching.toRange
 import org.jetbrains.kotlin.psi.*
@@ -30,7 +31,10 @@ public class MergeWhenIntention : JetSelfTargetingRangeIntention<JetWhenExpressi
     override fun applicabilityRange(element: JetWhenExpression): TextRange? {
         val next = PsiTreeUtil.skipSiblingsForward(element, javaClass<PsiWhiteSpace>()) as? JetWhenExpression ?: return null
 
-        if (!element.getSubjectExpression().matches(next.getSubjectExpression())) return null
+        val subject1 = element.getSubjectExpression()
+        val subject2 = next.getSubjectExpression()
+        if (!subject1.matches(subject2)) return null
+        if (subject1 != null && !subject1.isStableVariable()) return null
 
         val entries1 = element.getEntries()
         val entries2 = next.getEntries()

idea/testData/intentions/branched/when/merge/mergeWithVarSubject.kt

@@ -0,0 +1,16 @@
+// IS_APPLICABLE: false
+fun doSomething<T>(a: T) {}
+
+fun test() {
+    var n = 0
+
+    <caret>when (n) {
+        1 -> n = 2
+        2 -> n = 1
+    }
+
+    when (n) {
+        1 -> doSomething("A")
+        2 -> doSomething("B")
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -1921,6 +1921,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("mergeWithVarSubject.kt")
+                public void testMergeWithVarSubject() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/branched/when/merge/mergeWithVarSubject.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("mergeWithoutSubject.kt")
                 public void testMergeWithoutSubject() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/branched/when/merge/mergeWithoutSubject.kt");