KT-7844 Completion for top level classes should propose the file name

#KT-7844 Fixed

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/BasicCompletionSession.kt

@@ -21,6 +21,7 @@ import com.intellij.codeInsight.completion.CompletionResultSet
 import com.intellij.codeInsight.completion.CompletionSorter
 import com.intellij.codeInsight.completion.CompletionType
 import com.intellij.codeInsight.lookup.LookupElement
+import com.intellij.codeInsight.lookup.LookupElementBuilder
 import com.intellij.codeInsight.template.TemplateManager
 import com.intellij.patterns.PatternCondition
 import com.intellij.patterns.StandardPatterns
@@ -43,6 +44,7 @@ import org.jetbrains.kotlin.psi.psiUtil.getNonStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.parents
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.renderer.render
 import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindExclude
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindFilter
@@ -63,6 +65,8 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
 
         PARAMETER_NAME(descriptorKindFilter = null),
 
+        TOP_LEVEL_CLASS_NAME(descriptorKindFilter = null),
+
         SUPER_QUALIFIER(descriptorKindFilter = DescriptorKindFilter.NON_SINGLETON_CLASSIFIERS)
     }
 
@@ -94,11 +98,16 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
 
     private fun detectCompletionKind(): CompletionKind {
         if (nameExpression == null) {
-            val parameter = position.getParent() as? KtParameter
+            return when  {
-            return if (parameter != null && position == parameter.getNameIdentifier())
+                (position.parent as? KtParameter)?.nameIdentifier == position ->
-                CompletionKind.PARAMETER_NAME
+                    CompletionKind.PARAMETER_NAME
-            else
+
-                CompletionKind.KEYWORDS_ONLY
+                (position.parent as? KtClassOrObject)?.nameIdentifier == position && position.parent.parent is KtFile ->
+                    CompletionKind.TOP_LEVEL_CLASS_NAME
+
+                else ->
+                    CompletionKind.KEYWORDS_ONLY
+            }
         }
 
         if (NamedArgumentCompletion.isOnlyNamedArgumentExpected(nameExpression)) {
@@ -155,6 +164,11 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
             return
         }
 
+        if (completionKind == CompletionKind.TOP_LEVEL_CLASS_NAME) {
+            completeTopLevelClassName()
+            return
+        }
+
         // if we are typing parameter name, restart completion each time we type an upper case letter because new suggestions will appear (previous words can be used as user prefix)
         if (parameterNameAndTypeCompletion != null) {
             val prefixPattern = StandardPatterns.string().with(object : PatternCondition<String>("Prefix ends with uppercase letter") {
@@ -344,6 +358,16 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
                 .forEach { collector.addElement(it) }
     }
 
+    private fun completeTopLevelClassName() {
+        val name = parameters.originalFile.virtualFile.nameWithoutExtension
+        if (!(Name.isValidIdentifier(name) && Name.identifier(name).render() == name && name[0].isUpperCase())) return
+        if ((parameters.originalFile as KtFile).declarations.any { it is KtClassOrObject && it.name == name }) return
+
+        val lookupElement = LookupElementBuilder.create(name)
+        lookupElement.putUserData(KotlinCompletionCharFilter.SUPPRESS_ITEM_SELECTION_BY_CHARS_ON_TYPING, Unit)
+        collector.addElement(lookupElement)
+    }
+
     override fun createSorter(): CompletionSorter {
         var sorter = super.createSorter()
 

idea/idea-completion/testData/basic/common/TopLevelClassName-3.kt

@@ -0,0 +1,3 @@
+class <caret>
+
+// NUMBER: 0

idea/idea-completion/testData/basic/common/TopLevelClassName1.kt

@@ -0,0 +1,3 @@
+class <caret>
+
+// EXIST: { lookupString: "TopLevelClassName1", itemText: "TopLevelClassName1"  }

idea/idea-completion/testData/basic/common/TopLevelClassName4.kt

@@ -0,0 +1,5 @@
+class A {
+    class <caret>
+}
+
+// NUMBER: 0

idea/idea-completion/testData/basic/common/TopLevelClassName5.kt

@@ -0,0 +1,6 @@
+class <caret>
+
+class TopLevelClassName5 {
+}
+
+// NUMBER: 0

idea/idea-completion/testData/basic/common/topLevelClassName2.kt

@@ -0,0 +1,3 @@
+class <caret>
+
+// NUMBER: 0

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JSBasicCompletionTestGenerated.java

@@ -691,6 +691,36 @@ public class JSBasicCompletionTestGenerated extends AbstractJSBasicCompletionTes
             doTest(fileName);
         }
 
+        @TestMetadata("TopLevelClassName1.kt")
+        public void testTopLevelClassName1() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName1.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("topLevelClassName2.kt")
+        public void testTopLevelClassName2() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/topLevelClassName2.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("TopLevelClassName4.kt")
+        public void testTopLevelClassName4() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName4.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("TopLevelClassName5.kt")
+        public void testTopLevelClassName5() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName5.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("TopLevelClassName-3.kt")
+        public void testTopLevelClassName_3() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName-3.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("TypeArgCompletionBug.kt")
         public void testTypeArgCompletionBug() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TypeArgCompletionBug.kt");

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JvmBasicCompletionTestGenerated.java

@@ -691,6 +691,36 @@ public class JvmBasicCompletionTestGenerated extends AbstractJvmBasicCompletionT
             doTest(fileName);
         }
 
+        @TestMetadata("TopLevelClassName1.kt")
+        public void testTopLevelClassName1() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName1.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("topLevelClassName2.kt")
+        public void testTopLevelClassName2() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/topLevelClassName2.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("TopLevelClassName4.kt")
+        public void testTopLevelClassName4() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName4.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("TopLevelClassName5.kt")
+        public void testTopLevelClassName5() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName5.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("TopLevelClassName-3.kt")
+        public void testTopLevelClassName_3() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TopLevelClassName-3.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("TypeArgCompletionBug.kt")
         public void testTypeArgCompletionBug() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/TypeArgCompletionBug.kt");