[Analysis API] optimize composite scope

Do not create KtCompositeScope for empty or single scopes

analysis/analysis-api-fe10/build.gradle.kts

@@ -41,6 +41,7 @@ tasks.withType<org.jetbrains.kotlin.gradle.dsl.KotlinCompile<*>> {
     kotlinOptions {
         freeCompilerArgs += "-opt-in=kotlin.RequiresOptIn"
         freeCompilerArgs += "-Xcontext-receivers"
+        freeCompilerArgs += "-opt-in=org.jetbrains.kotlin.analysis.api.KtAnalysisApiInternals"
     }
 }
 

analysis/analysis-api-fe10/src/org/jetbrains/kotlin/analysis/api/descriptors/components/KtFe10ScopeProvider.kt

@@ -181,7 +181,7 @@ internal class KtFe10ScopeProvider(
     }
 
     override fun getCompositeScope(subScopes: List<KtScope>): KtScope {
-        return KtCompositeScope(subScopes, token)
+        return KtCompositeScope.create(subScopes, token)
     }
 
     override fun getTypeScope(type: KtType): KtTypeScope {
@@ -201,12 +201,12 @@ internal class KtFe10ScopeProvider(
         val scopeKind = KtScopeKind.LocalScope(0) // TODO
         val lexicalScope = positionInFakeFile.getResolutionScope(bindingContext)
         if (lexicalScope != null) {
-            val compositeScope = KtCompositeScope(listOf(KtFe10ScopeLexical(lexicalScope, analysisContext)), token)
+            val compositeScope = KtCompositeScope.create(listOf(KtFe10ScopeLexical(lexicalScope, analysisContext)), token)
             return KtScopeContext(listOf(KtScopeWithKind(compositeScope, scopeKind, token)), collectImplicitReceivers(lexicalScope), token)
         }
 
         val fileScope = analysisContext.resolveSession.fileScopeProvider.getFileResolutionScope(originalFile)
-        val compositeScope = KtCompositeScope(listOf(KtFe10ScopeLexical(fileScope, analysisContext)), token)
+        val compositeScope = KtCompositeScope.create(listOf(KtFe10ScopeLexical(fileScope, analysisContext)), token)
         return KtScopeContext(listOf(KtScopeWithKind(compositeScope, scopeKind, token)), collectImplicitReceivers(fileScope), token)
     }
 

analysis/analysis-api-fir/build.gradle.kts

@@ -95,4 +95,5 @@ compileKotlin.dependsOn(generateCode)
 
 tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
     kotlinOptions.freeCompilerArgs += "-Xcontext-receivers"
+    kotlinOptions.freeCompilerArgs += "-opt-in=org.jetbrains.kotlin.analysis.api.KtAnalysisApiInternals"
 }

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/components/KtFirScopeProvider.kt

@@ -156,7 +156,7 @@ internal class KtFirScopeProvider(
 
 
     override fun getCompositeScope(subScopes: List<KtScope>): KtScope {
-        return KtCompositeScope(subScopes, token)
+        return KtCompositeScope.create(subScopes, token)
     }
 
     override fun getTypeScope(type: KtType): KtTypeScope? = getFirTypeScope(type)?.let { convertToKtTypeScope(it) }

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/components/KtFirScopeSubstitution.kt

@@ -24,7 +24,7 @@ internal class KtFirScopeSubstitution(
     override fun getDeclarationScope(scope: KtTypeScope): KtScope {
         return when (scope) {
             is KtFirDelegatingTypeScope -> KtFirDelegatingNamesAwareScope(scope.firScope, analysisSession.firSymbolBuilder)
-            is KtCompositeTypeScope -> KtCompositeScope(scope.subScopes.map(::getDeclarationScope), token)
+            is KtCompositeTypeScope -> KtCompositeScope.create(scope.subScopes.map(::getDeclarationScope), token)
             else -> unexpectedElementError<KtTypeScope>(scope)
         }
     }

analysis/analysis-api-impl-base/build.gradle.kts

@@ -35,6 +35,7 @@ sourceSets {
 
 tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
     kotlinOptions.freeCompilerArgs += "-Xcontext-receivers"
+    kotlinOptions.freeCompilerArgs += "-opt-in=org.jetbrains.kotlin.analysis.api.KtAnalysisApiInternals"
 }
 
 testsJar()

analysis/analysis-api-impl-base/src/org/jetbrains/kotlin/analysis/api/impl/base/scopes/KtCompositeScope.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.analysis.api.impl.base.scopes
 
+import org.jetbrains.kotlin.analysis.api.KtAnalysisApiInternals
 import org.jetbrains.kotlin.analysis.api.lifetime.KtLifetimeToken
 import org.jetbrains.kotlin.analysis.api.lifetime.withValidityAssertion
 import org.jetbrains.kotlin.analysis.api.scopes.KtScope
@@ -12,10 +13,18 @@ import org.jetbrains.kotlin.analysis.api.scopes.KtScopeNameFilter
 import org.jetbrains.kotlin.analysis.api.symbols.*
 import org.jetbrains.kotlin.name.Name
 
-class KtCompositeScope(
+@KtAnalysisApiInternals
+class KtCompositeScope private constructor(
     private val subScopes: List<KtScope>,
-    override val token: KtLifetimeToken
+    override val token: KtLifetimeToken,
 ) : KtScope {
+
+    init {
+        require(subScopes.size > 1) {
+            "Required `subScopes.size > 1` but `subScopes.size = ${subScopes.size}`"
+        }
+    }
+
     override fun getAllPossibleNames(): Set<Name> = withValidityAssertion {
         buildSet {
             subScopes.flatMapTo(this) { it.getAllPossibleNames() }
@@ -81,4 +90,13 @@ class KtCompositeScope(
     override fun mayContainName(name: Name): Boolean = withValidityAssertion {
         subScopes.any { it.mayContainName(name) }
     }
+
+    companion object {
+        fun create(subScopes: List<KtScope>, token: KtLifetimeToken): KtScope =
+            when (subScopes.size) {
+                0 -> KtEmptyScope(token)
+                1 -> subScopes.single()
+                else -> KtCompositeScope(subScopes, token)
+            }
+    }
 }