Completion after "this@" includes immediate this too

#KT-6836 Fixed

idea/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt

@@ -294,7 +294,7 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
                     // if "this" is parsed correctly in the current context - insert it and all this@xxx items
                     "this" -> {
                         if (expression != null) {
-                            collector.addElements(thisExpressionItems(bindingContext!!, expression).map { it.factory() })
+                            collector.addElements(thisExpressionItems(bindingContext!!, expression, prefix).map { it.factory() })
                         }
                     }
 

idea/src/org/jetbrains/kotlin/idea/completion/CompletionUtils.kt

@@ -212,22 +212,27 @@ fun shouldCompleteThisItems(prefixMatcher: PrefixMatcher): Boolean {
 
 data class ThisItemInfo(val factory: () -> LookupElement, val type: FuzzyType)
 
-fun thisExpressionItems(bindingContext: BindingContext, position: JetExpression): Collection<ThisItemInfo> {
+fun thisExpressionItems(bindingContext: BindingContext, position: JetExpression, prefix: String): Collection<ThisItemInfo> {
     val scope = bindingContext[BindingContext.RESOLUTION_SCOPE, position] ?: return listOf()
 
     val result = ArrayList<ThisItemInfo>()
     for ((i, receiver) in scope.getImplicitReceiversWithInstance().withIndex()) {
         val thisType = receiver.getType()
         val fuzzyType = FuzzyType(thisType, listOf())
-        val label = if (i == 0) null else (thisQualifierName(receiver) ?: continue)
 
-        fun createLookupElement(): LookupElement {
+        fun createLookupElement(label: String?): LookupElement {
             var element = createKeywordWithLabelElement("this", label)
             element = element.withTypeText(DescriptorRenderer.SHORT_NAMES_IN_TYPES.renderType(thisType))
             return element
         }
 
-        result.add(ThisItemInfo({ createLookupElement() }, fuzzyType))
+        if (i == 0) {
+            result.add(ThisItemInfo({ createLookupElement(null) }, fuzzyType))
+            if (!prefix.startsWith("this@")) continue // if prefix does not start with "this@" do not include immediate this in the form with label
+        }
+
+        val label = thisQualifierName(receiver) ?: continue
+        result.add(ThisItemInfo({ createLookupElement(label) }, fuzzyType))
     }
     return result
 }

idea/src/org/jetbrains/kotlin/idea/completion/smart/SmartCompletion.kt

@@ -185,7 +185,7 @@ class SmartCompletion(
 
     private fun MutableCollection<LookupElement>.addThisItems(place: JetExpression, expectedInfos: Collection<ExpectedInfo>) {
         if (shouldCompleteThisItems(prefixMatcher)) {
-            val items = thisExpressionItems(bindingContext, place)
+            val items = thisExpressionItems(bindingContext, place, prefixMatcher.getPrefix())
             for ((factory, type) in items) {
                 val classifier = { (expectedInfo: ExpectedInfo) -> type.classifyExpectedInfo(expectedInfo) }
                 addLookupElements(null, expectedInfos, classifier) {

idea/testData/completion/keywords/QualifiedThis.kt

@@ -7,7 +7,7 @@ class Outer {
 }
 
 // ABSENT: this
-// ABSENT: "this@foo"
+// EXIST: { lookupString: "this@foo", itemText: "this", tailText: "@foo", typeText: "String", attributes: "bold" }
 // EXIST: { lookupString: "this@Inner", itemText: "this", tailText: "@Inner", typeText: "Outer.Inner", attributes: "bold" }
 // EXIST: { lookupString: "this@Outer", itemText: "this", tailText: "@Outer", typeText: "Outer", attributes: "bold" }
-// NUMBER: 2
+// NUMBER: 3

idea/testData/completion/keywords/QualifiedThisInAccessor.kt

@@ -0,0 +1,5 @@
+val String.foo: Int
+    get() = this@<caret>.length()
+
+// EXIST: "this@foo"
+// NUMBER: 1

idea/testData/completion/smart/this/QualifiedThis.kt

@@ -7,7 +7,7 @@ class Outer {
 }
 
 // ABSENT: this
-// ABSENT: "this@foo"
+// EXIST: { lookupString: "this@foo", itemText: "this", tailText: "@foo", typeText: "String", attributes: "bold" }
 // EXIST: { lookupString: "this@Inner", itemText: "this", tailText: "@Inner", typeText: "Outer.Inner", attributes: "bold" }
 // EXIST: { lookupString: "this@Outer", itemText: "this", tailText: "@Outer", typeText: "Outer", attributes: "bold" }
-// NUMBER: 2
+// NUMBER: 3

idea/tests/org/jetbrains/kotlin/completion/KeywordCompletionTestGenerated.java

@@ -330,6 +330,12 @@ public class KeywordCompletionTestGenerated extends AbstractKeywordCompletionTes
         doTest(fileName);
     }
 
+    @TestMetadata("QualifiedThisInAccessor.kt")
+    public void testQualifiedThisInAccessor() throws Exception {
+        String fileName = JetTestUtils.navigationMetadata("idea/testData/completion/keywords/QualifiedThisInAccessor.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("Return1.kt")
     public void testReturn1() throws Exception {
         String fileName = JetTestUtils.navigationMetadata("idea/testData/completion/keywords/Return1.kt");