Transform 'if' to 'when' with subject if possible

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

@@ -110,7 +110,12 @@ public class IfWhenUtils {
             }
         } while (currIfExpression != null);
 
-        ifExpression.replace(builder.toExpression(ifExpression.getProject()));
+        JetWhenExpression whenExpression = builder.toExpression(ifExpression.getProject());
+        if (WhenUtils.checkIntroduceWhenSubject(whenExpression)) {
+            whenExpression = WhenUtils.introduceWhenSubject(whenExpression);
+        }
+
+        ifExpression.replace(whenExpression);
     }
 
     private static String combineWhenConditions(JetWhenCondition[] conditions, JetExpression subject) {

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

@@ -86,7 +86,8 @@ public class WhenUtils {
         return whenExpression.getSubjectExpression() instanceof JetSimpleNameExpression;
     }
 
-    public static void flattenWhen(@NotNull JetWhenExpression whenExpression) {
+    @NotNull
+    public static JetWhenExpression flattenWhen(@NotNull JetWhenExpression whenExpression) {
         JetExpression subjectExpression = whenExpression.getSubjectExpression();
 
         JetExpression elseBranch = whenExpression.getElseExpression();
@@ -109,10 +110,14 @@ public class WhenUtils {
             builder.entry(entry);
         }
 
-        whenExpression.replace(builder.toExpression(whenExpression.getProject()));
+        JetWhenExpression newWhenExpression = builder.toExpression(whenExpression.getProject());
+        whenExpression.replace(newWhenExpression);
+
+        return newWhenExpression;
     }
 
-    public static void introduceWhenSubject(@NotNull JetWhenExpression whenExpression) {
+    @NotNull
+    public static JetWhenExpression introduceWhenSubject(@NotNull JetWhenExpression whenExpression) {
         JetExpression subject = getWhenSubjectCandidate(whenExpression);
         assertNotNull(subject);
 
@@ -158,9 +163,13 @@ public class WhenUtils {
             builder.branchExpression(branchExpression);
         }
 
-        whenExpression.replace(builder.toExpression(whenExpression.getProject()));
+        JetWhenExpression newWhenExpression = builder.toExpression(whenExpression.getProject());
+        whenExpression.replace(newWhenExpression);
+
+        return newWhenExpression;
     }
 
+    @NotNull
     static String whenConditionToExpressionText(@NotNull JetWhenCondition condition, JetExpression subject) {
         if (condition instanceof JetWhenConditionIsPattern) {
             JetWhenConditionIsPattern patternCondition = (JetWhenConditionIsPattern) condition;
@@ -182,7 +191,8 @@ public class WhenUtils {
         return conditionExpression != null ? conditionExpression.getText() : "";
     }
 
-    public static void eliminateWhenSubject(@NotNull JetWhenExpression whenExpression) {
+    @NotNull
+    public static JetWhenExpression eliminateWhenSubject(@NotNull JetWhenExpression whenExpression) {
         JetExpression subject = whenExpression.getSubjectExpression();
         assertNotNull(subject);
 
@@ -204,6 +214,9 @@ public class WhenUtils {
             builder.branchExpression(branchExpression);
         }
 
-        whenExpression.replace(builder.toExpression(whenExpression.getProject()));
+        JetWhenExpression newWhenExpression = builder.toExpression(whenExpression.getProject());
+        whenExpression.replace(newWhenExpression);
+
+        return newWhenExpression;
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithEqualityTests.kt.after

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

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithIs.kt.after

@@ -1,8 +1,8 @@
 fun test(obj: Any): String {
-    return <caret>when {
-        obj is String -> "string"
-        obj is Int -> "int"
-        obj is Class<*> -> "class"
+    return <caret>when (obj) {
+        is String -> "string"
+        is Int -> "int"
+        is Class<*> -> "class"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithNegativeIs.kt.after

@@ -1,8 +1,8 @@
 fun test(obj: Any): String {
-    return <caret>when {
-        obj !is Iterable<*> -> "not iterable"
-        obj !is Collection<*> -> "not collection"
-        obj !is MutableCollection<*> -> "not mutable collection"
+    return <caret>when (obj) {
+        !is Iterable<*> -> "not iterable"
+        !is Collection<*> -> "not collection"
+        !is MutableCollection<*> -> "not mutable collection"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithNegativeRangeTests.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n !in 0..1000 -> "unknown"
-        n !in 0..100 -> "big"
-        n !in 0..10 -> "average"
+    return <caret>when (n) {
+        !in 0..1000 -> "unknown"
+        !in 0..100 -> "big"
+        !in 0..10 -> "average"
         else -> "small"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithRangeTests.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n in 0..10 -> "small"
-        n in 10..100 -> "average"
-        n in 100..1000 -> "big"
+    return <caret>when (n) {
+        in 0..10 -> "small"
+        in 10..100 -> "average"
+        in 100..1000 -> "big"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithRangeTestsAndMultiConditions.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n in 0..5, n in 5..10 -> "small"
-        n in 10..50, n in 50..100 -> "average"
-        n in 100..500, n in 500..1000 -> "big"
+    return <caret>when (n) {
+        in 0..5, in 5..10 -> "small"
+        in 10..50, in 50..100 -> "average"
+        in 100..500, in 500..1000 -> "big"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithRangeTestsAndUnparenthesizedMultiConditions.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n in 0..5, n in 5..10 -> "small"
-        n in 10..50, n in 50..100 -> "average"
-        n in 100..500, n in 500..1000 -> "big"
+    return <caret>when (n) {
+        in 0..5, in 5..10 -> "small"
+        in 10..50, in 50..100 -> "average"
+        in 100..500, in 500..1000 -> "big"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/whenWithMultipleConditionTypes.kt.after

@@ -1,12 +1,12 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n !is Int -> "???"
-        n in 0..10 -> "small"
-        n in 10..100 -> "average"
-        n in 100..1000 -> "big"
-        n == 1000000 -> "million"
-        n !in -100..-10 -> "good"
-        n is Int -> "unknown"
+    return <caret>when (n) {
+        !is Int -> "???"
+        in 0..10 -> "small"
+        in 10..100 -> "average"
+        in 100..1000 -> "big"
+        1000000 -> "million"
+        !in -100..-10 -> "good"
+        is Int -> "unknown"
         else -> "unknown"
     }
 }