Introduce 'when' subject: consider equality right-hand side as subject candidate

idea/src/org/jetbrains/jet/plugin/codeInsight/codeTransformations/branchedTransformations/WhenUtils.java

@@ -28,9 +28,14 @@ public class WhenUtils {
 
         if (condition instanceof JetBinaryExpression) {
             JetBinaryExpression binaryExpression = (JetBinaryExpression) condition;
+            JetExpression lhs = binaryExpression.getLeft();
+
             IElementType op = binaryExpression.getOperationToken();
-            if (op == JetTokens.EQEQ || op == JetTokens.IN_KEYWORD || op == JetTokens.NOT_IN) {
-                return ((JetBinaryExpression) condition).getLeft();
+            if (op == JetTokens.IN_KEYWORD || op == JetTokens.NOT_IN) {
+                return lhs;
+            }
+            if (op == JetTokens.EQEQ) {
+                return lhs instanceof JetSimpleNameExpression ? lhs : binaryExpression.getRight();
             }
         }
 
@@ -144,6 +149,7 @@ public class WhenUtils {
                 else if (conditionExpression instanceof JetBinaryExpression) {
                     JetBinaryExpression binaryExpression = (JetBinaryExpression) conditionExpression;
 
+                    JetExpression lhs = binaryExpression.getLeft();
                     JetExpression rhs = binaryExpression.getRight();
 
                     IElementType op = binaryExpression.getOperationToken();
@@ -154,7 +160,11 @@ public class WhenUtils {
                         builder.range(rhs, true);
                     }
                     else if (op == JetTokens.EQEQ) {
-                        builder.condition(rhs);
+                        if (JetPsiMatcher.checkElementMatch(subject, lhs)) {
+                            builder.condition(rhs);
+                        } else {
+                            builder.condition(lhs);
+                        }
                     }
                     else assert false : TRANSFORM_WITHOUT_CHECK;
                 }

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithMultipleConditionTypes.kt

@@ -5,6 +5,7 @@ fun test(n: Int): String {
         n in 10..100 -> "average"
         n in 100..1000 -> "big"
         n == 1000000 -> "million"
+        2000000 == n -> "two millions"
         n !in -100..-10 -> "good"
         n is Int -> "unknown"
         else -> "unknown"

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithMultipleConditionTypes.kt.after

@@ -5,6 +5,7 @@ fun test(n: Int): String {
         in 10..100 -> "average"
         in 100..1000 -> "big"
         1000000 -> "million"
+        2000000 -> "two millions"
         !in -100..-10 -> "good"
         is Int -> "unknown"
         else -> "unknown"

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithSwappedEqualityTests.kt

@@ -0,0 +1,8 @@
+fun test(n: Int): String {
+    return <caret>when {
+        n == 0 -> "zero"
+        1 == n -> "one"
+        n == 2 -> "two"
+        else -> "unknown"
+    }
+}

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithSwappedEqualityTests.kt.after

@@ -0,0 +1,8 @@
+fun test(n: Int): String {
+    return <caret>when (n) {
+        0 -> "zero"
+        1 -> "one"
+        2 -> "two"
+        else -> "unknown"
+    }
+}

idea/tests/org/jetbrains/jet/plugin/codeInsight/codeTransformations/CodeTransformationsTestGenerated.java

@@ -585,6 +585,11 @@ public class CodeTransformationsTestGenerated extends AbstractCodeTransformation
             doTestIntroduceWhenSubject("idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithSubject.kt");
         }
         
+        @TestMetadata("whenWithSwappedEqualityTests.kt")
+        public void testWhenWithSwappedEqualityTests() throws Exception {
+            doTestIntroduceWhenSubject("idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithSwappedEqualityTests.kt");
+        }
+        
         @TestMetadata("whenWithUnmatchedCandidateSubjects.kt")
         public void testWhenWithUnmatchedCandidateSubjects() throws Exception {
             doTestIntroduceWhenSubject("idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithUnmatchedCandidateSubjects.kt");