Inline Variable: Show error message on attempt to inline unused declaration

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

@@ -71,6 +71,11 @@ class KotlinInlineValHandler : InlineActionHandler() {
             (it.element as? KtExpression)?.getQualifiedExpressionForSelectorOrThis()
         }
 
+        if (referenceExpressions.isEmpty()) {
+            val kind = if (declaration.isLocal) "Variable" else "Property"
+            return showErrorHint(project, editor, "$kind '$name' is never used")
+        }
+
         val assignments = Sets.newHashSet<PsiElement>()
         referenceExpressions.forEach { expression ->
             val parent = expression.parent
@@ -120,6 +125,8 @@ class KotlinInlineValHandler : InlineActionHandler() {
             assignments.forEach { it.delete() }
             declaration.delete()
 
+            if (inlinedExpressions.isEmpty()) return@executeWriteCommand
+
             typeArgumentsForCall?.let { addTypeArguments(it, inlinedExpressions) }
 
             parametersForFunctionLiteral?.let { addFunctionLiteralParameterTypes(it, inlinedExpressions) }

idea/testData/refactoring/inline/noUsages.kt

@@ -0,0 +1,4 @@
+// ERROR: Variable 'a' is never used
+fun foo() {
+    val <caret>a = 1 + 2
+}

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

@@ -83,6 +83,12 @@ public class InlineTestGenerated extends AbstractInlineTest {
         doTest(fileName);
     }
 
+    @TestMetadata("noUsages.kt")
+    public void testNoUsages() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/inline/noUsages.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("Parameter.kt")
     public void testParameter() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/inline/Parameter.kt");