"Eliminate argument of 'when'": do not suggest if 'when' is used as expression and it has no 'else' branch (#2898)

#KT-35526 Fixed

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

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.idea.intentions.branchedTransformations.intentions
 import com.intellij.codeInsight.intention.LowPriorityAction
 import com.intellij.openapi.editor.Editor
 import org.jetbrains.kotlin.idea.KotlinBundle
+import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.intentions.SelfTargetingIntention
 import org.jetbrains.kotlin.idea.intentions.branchedTransformations.toExpression
 import org.jetbrains.kotlin.idea.util.CommentSaver
@@ -16,6 +17,8 @@ import org.jetbrains.kotlin.psi.KtPsiFactory
 import org.jetbrains.kotlin.psi.KtWhenExpression
 import org.jetbrains.kotlin.psi.buildExpression
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.resolve.bindingContextUtil.isUsedAsExpression
+import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 
 class EliminateWhenSubjectIntention :
     SelfTargetingIntention<KtWhenExpression>(KtWhenExpression::class.java, KotlinBundle.lazyMessage("eliminate.argument.of.when")),
@@ -23,7 +26,10 @@ class EliminateWhenSubjectIntention :
     override fun isApplicableTo(element: KtWhenExpression, caretOffset: Int): Boolean {
         if (element.subjectExpression !is KtNameReferenceExpression) return false
         val lBrace = element.openBrace ?: return false
-        return caretOffset <= lBrace.startOffset
+        if (caretOffset > lBrace.startOffset) return false
+        val lastEntry = element.entries.lastOrNull()
+        if (lastEntry?.isElse != true && element.isUsedAsExpression(element.analyze(BodyResolveMode.PARTIAL_WITH_CFA))) return false
+        return true
     }
 
     override fun applyTo(element: KtWhenExpression, editor: Editor?) {

idea/testData/intentions/branched/when/eliminateSubject/withoutElse.kt

@@ -0,0 +1,11 @@
+enum class Type {
+    HYDRO,
+    PYRO
+}
+
+fun select(t: Type) {
+    <caret>when (t) {
+        Type.HYDRO -> 1
+        Type.PYRO -> 42
+    }
+}

idea/testData/intentions/branched/when/eliminateSubject/withoutElse.kt.after

@@ -0,0 +1,11 @@
+enum class Type {
+    HYDRO,
+    PYRO
+}
+
+fun select(t: Type) {
+    when {
+        t == Type.HYDRO -> 1
+        t == Type.PYRO -> 42
+    }
+}

idea/testData/intentions/branched/when/eliminateSubject/withoutElseUsedAsExpression.kt

@@ -0,0 +1,12 @@
+// IS_APPLICABLE: false
+enum class Type {
+    HYDRO,
+    PYRO
+}
+
+fun select(t: Type): Int {
+    return <caret>when (t) {
+        Type.HYDRO -> 1
+        Type.PYRO -> 42
+    }
+}

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

@@ -3267,6 +3267,16 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                 public void testWhenWithoutSubject() throws Exception {
                     runTest("idea/testData/intentions/branched/when/eliminateSubject/whenWithoutSubject.kt");
                 }
+
+                @TestMetadata("withoutElse.kt")
+                public void testWithoutElse() throws Exception {
+                    runTest("idea/testData/intentions/branched/when/eliminateSubject/withoutElse.kt");
+                }
+
+                @TestMetadata("withoutElseUsedAsExpression.kt")
+                public void testWithoutElseUsedAsExpression() throws Exception {
+                    runTest("idea/testData/intentions/branched/when/eliminateSubject/withoutElseUsedAsExpression.kt");
+                }
             }
 
             @TestMetadata("idea/testData/intentions/branched/when/flatten")