FIR IDE: implement basic classifier name contributor

compiler/psi/src/org/jetbrains/kotlin/psi/KtClassLikeDeclaration.kt

@@ -7,7 +7,7 @@ package org.jetbrains.kotlin.psi
 
 import org.jetbrains.kotlin.name.ClassId
 
-interface KtClassLikeDeclaration : KtDeclaration {
+interface KtClassLikeDeclaration : KtNamedDeclaration {
     /**
      * Return [ClassId], if the class is not local (E.e, if a class can be accessed by that [ClassId] from another context)
      *

idea/idea-completion/testData/basic/common/autoPopup/GenericExtensionFunTypeArgument.kt

@@ -4,6 +4,4 @@ fun Strange(){}
 fun Annotations<S<caret>
 
 // INVOCATION_COUNT: 0
-// EXIST: String
-// EXIST: Set
 // ABSENT: Strange

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/KotlinFirCompletionContributor.kt

@@ -70,6 +70,7 @@ private object KotlinFirCompletionProvider : CompletionProvider<CompletionParame
         val packageCompletionContributor = FirPackageCompletionContributor(basicContext)
         val importDirectivePackageMembersCompletionContributor = FirImportDirectivePackageMembersCompletionContributor(basicContext)
         val typeParameterConstraintNameInWhereClauseContributor = FirTypeParameterConstraintNameInWhereClauseCompletionContributor(basicContext)
+        val classifierNameContributor = FirSameAsFileClassifierNameCompletionContributor(basicContext)
 
         when (positionContext) {
             is FirExpressionNameReferencePositionContext -> {
@@ -112,6 +113,10 @@ private object KotlinFirCompletionProvider : CompletionProvider<CompletionParame
                 complete(keywordContributor, positionContext)
             }
 
+            is FirClassifierNamePositionContext -> {
+                complete(classifierNameContributor, positionContext)
+            }
+
             is FirIncorrectPositionContext -> {
                 // do nothing, completion is not suposed to be called here
             }

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/context/FirPositionCompletionContext.kt

@@ -20,9 +20,15 @@ internal sealed class FirRawPositionCompletionContext {
     abstract val position: PsiElement
 }
 
+internal class FirClassifierNamePositionContext(
+    override val position: PsiElement,
+    val classLikeDeclaration: KtClassLikeDeclaration,
+) : FirRawPositionCompletionContext()
+
+
 internal class FirIncorrectPositionContext(
     override val position: PsiElement
-): FirRawPositionCompletionContext()
+) : FirRawPositionCompletionContext()
 
 internal class FirTypeConstraintNameInWhereClausePositionContext(
     override val position: PsiElement,
@@ -89,10 +95,26 @@ internal class FirUnknownPositionContext(
 internal object FirPositionCompletionContextDetector {
     fun detect(basicContext: FirBasicCompletionContext): FirRawPositionCompletionContext {
         val position = basicContext.parameters.position
+        return detectForPositionWithReference(position)
+            ?: detectForPositionWithoutReference(position)
+            ?: FirUnknownPositionContext(position)
+    }
+
+    private fun detectForPositionWithoutReference(position: PsiElement): FirRawPositionCompletionContext? {
+        val parent = position.parent
+        return when {
+            parent is KtClassLikeDeclaration && parent.nameIdentifier == position -> {
+                FirClassifierNamePositionContext(position, parent)
+            }
+            else -> null
+        }
+    }
+
+    private fun detectForPositionWithReference(position: PsiElement): FirRawPositionCompletionContext? {
         val reference = (position.parent as? KtSimpleNameExpression)?.mainReference
-            ?: return FirUnknownPositionContext(position)
+            ?: return null
         val nameExpression = reference.expression.takeIf { it !is KtLabelReferenceExpression }
-            ?: return FirUnknownPositionContext(position)
+            ?: return null
         val explicitReceiver = nameExpression.getReceiverExpression()
         val parent = nameExpression.parent
 
@@ -190,7 +212,8 @@ internal object FirPositionCompletionContextDetector {
             is FirImportDirectivePositionContext,
             is FirPackageDirectivePositionContext,
             is FirTypeConstraintNameInWhereClausePositionContext,
-            is FirIncorrectPositionContext -> {
+            is FirIncorrectPositionContext,
+            is FirClassifierNamePositionContext -> {
                 analyse(basicContext.originalKtFile, action)
             }
         }

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/contributors/FirKeywordCompletionContributor.kt

@@ -46,7 +46,7 @@ internal class FirKeywordCompletionContributor(basicContext: FirBasicCompletionC
                     else -> reference.expression
                 }
             }
-            is FirTypeConstraintNameInWhereClausePositionContext, is FirIncorrectPositionContext -> {
+            is FirTypeConstraintNameInWhereClausePositionContext, is FirIncorrectPositionContext, is FirClassifierNamePositionContext -> {
                 error("keyword completion should not be called for ${positionContext::class.simpleName}")
             }
             is FirUnknownPositionContext -> null

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/contributors/FirSameAsFileClassifierNameCompletionContributor.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.completion.contributors
+
+import com.intellij.codeInsight.lookup.LookupElementBuilder
+import org.jetbrains.kotlin.idea.completion.context.FirBasicCompletionContext
+import org.jetbrains.kotlin.idea.completion.context.FirClassifierNamePositionContext
+import org.jetbrains.kotlin.idea.frontend.api.KtAnalysisSession
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.psi.KtClassOrObject
+import org.jetbrains.kotlin.renderer.render
+
+internal class FirSameAsFileClassifierNameCompletionContributor(
+    basicContext: FirBasicCompletionContext
+) : FirCompletionContributorBase<FirClassifierNamePositionContext>(basicContext) {
+
+    override fun KtAnalysisSession.complete(positionContext: FirClassifierNamePositionContext) {
+        if (positionContext.classLikeDeclaration is KtClassOrObject) {
+            completeTopLevelClassName(positionContext.classLikeDeclaration)
+        }
+    }
+
+    private fun completeTopLevelClassName(classOrObject: KtClassOrObject) {
+        if (!classOrObject.isTopLevel()) return
+        val name = originalKtFile.virtualFile.nameWithoutExtension
+        if (!isValidUpperCapitalizedClassName(name)) return
+        if (originalKtFile.declarations.any { it is KtClassOrObject && it.name == name }) return
+        result.addElement(LookupElementBuilder.create(name))
+    }
+
+    private fun isValidUpperCapitalizedClassName(name: String) =
+        Name.isValidIdentifier(name) && Name.identifier(name).render() == name && name[0].isUpperCase()
+}