Inline variable: fix it works correctly for 'when' subject variable

#KT-29870 Fixed

idea/src/org/jetbrains/kotlin/idea/refactoring/inline/KotlinInlineCallableProcessor.kt

@@ -40,7 +40,8 @@ class KotlinInlineCallableProcessor(
     private val reference: KtSimpleNameReference?,
     private val inlineThisOnly: Boolean,
     private val deleteAfter: Boolean,
-    private val statementToDelete: KtBinaryExpression? = null
+    private val statementToDelete: KtBinaryExpression? = null,
+    private val postAction: (KtCallableDeclaration) -> Unit = {}
 ) : BaseRefactoringProcessor(project) {
 
     private val kind = when (declaration) {
@@ -82,6 +83,7 @@ class KotlinInlineCallableProcessor(
                         )
                     }
                 }
+                postAction(declaration)
             }
         )
     }

idea/src/org/jetbrains/kotlin/idea/refactoring/inline/KotlinInlineValDialog.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.idea.refactoring.KotlinRefactoringSettings
 import org.jetbrains.kotlin.idea.references.KtSimpleNameReference
 import org.jetbrains.kotlin.psi.KtBinaryExpression
 import org.jetbrains.kotlin.psi.KtProperty
+import org.jetbrains.kotlin.psi.KtWhenExpression
 
 class KotlinInlineValDialog(
     property: KtProperty,
@@ -66,12 +67,20 @@ class KotlinInlineValDialog(
     override fun isInlineThis() = KotlinRefactoringSettings.instance.INLINE_LOCAL_THIS
 
     public override fun doAction() {
+        val isWhenSubjectVariable = (callable.parent as? KtWhenExpression)?.subjectVariable == callable
+        val deleteAfter = !isInlineThisOnly && !isKeepTheDeclaration
         invokeRefactoring(
             KotlinInlineCallableProcessor(
                 project, replacementStrategy, callable, reference,
                 inlineThisOnly = isInlineThisOnly,
-                deleteAfter = !isInlineThisOnly && !isKeepTheDeclaration,
-                statementToDelete = assignmentToDelete
+                deleteAfter = deleteAfter && !isWhenSubjectVariable,
+                statementToDelete = assignmentToDelete,
+                postAction = { declaration ->
+                    if (deleteAfter && isWhenSubjectVariable) {
+                        val property = declaration as? KtProperty
+                        property?.initializer?.let { property.replace(it) }
+                    }
+                }
             )
         )
 

idea/testData/inspectionsLocal/unnecessaryVariable/whenSubject.kt

@@ -0,0 +1,7 @@
+fun test(value: Any): String {
+    return when (val <caret>v = value) {
+        is String -> "$v is String"
+        is Int -> "$v is Int"
+        else -> "$v"
+    }
+}

idea/testData/inspectionsLocal/unnecessaryVariable/whenSubject.kt.after

@@ -0,0 +1,7 @@
+fun test(value: Any): String {
+    return when (value) {
+        is String -> "$value is String"
+        is Int -> "$value is Int"
+        else -> "$value"
+    }
+}

idea/testData/refactoring/inline/inlineVariableOrProperty/whenSubject.kt

@@ -0,0 +1,7 @@
+fun test(s: String) {
+    when (val x = s.length) {
+        1 -> println("one")
+        2 -> println("two")
+        else -> println(x<caret>)
+    }
+}

idea/testData/refactoring/inline/inlineVariableOrProperty/whenSubject.kt.after

@@ -0,0 +1,7 @@
+fun test(s: String) {
+    when (s.length) {
+        1 -> println("one")
+        2 -> println("two")
+        else -> println(s.length)
+    }
+}

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

@@ -12924,6 +12924,11 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
         public void testVarCopy() throws Exception {
             runTest("idea/testData/inspectionsLocal/unnecessaryVariable/varCopy.kt");
         }
+
+        @TestMetadata("whenSubject.kt")
+        public void testWhenSubject() throws Exception {
+            runTest("idea/testData/inspectionsLocal/unnecessaryVariable/whenSubject.kt");
+        }
     }
 
     @TestMetadata("idea/testData/inspectionsLocal/unsafeCastFromDynamic")

idea/tests/org/jetbrains/kotlin/idea/refactoring/inline/InlineTestGenerated.java

@@ -620,6 +620,11 @@ public class InlineTestGenerated extends AbstractInlineTest {
             runTest("idea/testData/refactoring/inline/inlineVariableOrProperty/varWithInc.kt");
         }
 
+        @TestMetadata("whenSubject.kt")
+        public void testWhenSubject() throws Exception {
+            runTest("idea/testData/refactoring/inline/inlineVariableOrProperty/whenSubject.kt");
+        }
+
         @TestMetadata("idea/testData/refactoring/inline/inlineVariableOrProperty/addParenthesis")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)