avoid unnecessary creation of empty containers

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyFileScope.kt

@@ -33,13 +33,13 @@ import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValue
 import java.util.ArrayList
 
-class LazyFileScope private(
-        private val scopeChain: List<JetScope>,
+class LazyFileScope private constructor(
+        scopeChain: List<JetScope>,
         private val aliasImportResolver: LazyImportResolver,
         private val allUnderImportResolver: LazyImportResolver,
         containingDeclaration: PackageFragmentDescriptor,
         debugName: String
-) : ChainedScope(containingDeclaration, debugName, *scopeChain.copyToArray()) {
+) : ChainedScope(containingDeclaration, debugName, *scopeChain.toTypedArray()) {
 
     public fun forceResolveAllImports() {
         aliasImportResolver.forceResolveAllContents()

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyImportScope.kt

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.resolve.scopes.DescriptorKindFilter
 import org.jetbrains.kotlin.resolve.scopes.JetScope
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValue
 import org.jetbrains.kotlin.utils.Printer
+import org.jetbrains.kotlin.util.collectionUtils.concat
 import java.util.HashSet
 import java.util.LinkedHashSet
 import kotlin.properties.Delegates
@@ -192,17 +193,18 @@ class LazyImportResolver(
             descriptorsSelector: (JetScope, Name) -> Collection<D>
     ): Collection<D> {
         return resolveSession.getStorageManager().compute {
-            val descriptors = HashSet<D>()
+            var descriptors: Collection<D>? = null
             for (directive in indexedImports.importsForName(name)) {
                 if (directive == directiveUnderResolve) {
                     // This is the recursion in imports analysis
                     throw IllegalStateException("Recursion while resolving many imports: " + directive.getText())
                 }
 
-                descriptors.addAll(descriptorsSelector(getImportScope(directive, lookupMode), name))
+                val descriptorsForImport = descriptorsSelector(getImportScope(directive, lookupMode), name)
+                descriptors = descriptors.concat(descriptorsForImport)
             }
 
-            descriptors
+            descriptors ?: emptySet<D>()
         }
     }
 

compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/WritableScopeImpl.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.utils.Printer
 
 import java.util.*
 import com.intellij.util.SmartList
+import org.jetbrains.kotlin.util.collectionUtils.concatInOrder
 
 // Reads from:
 // 1. Maps
@@ -110,12 +111,8 @@ public class WritableScopeImpl(override val workerScope: JetScope,
 
         val labelsToDescriptors = getLabelsToDescriptors()
         val name = descriptor.getName()
-        var declarationDescriptors = labelsToDescriptors[name]
-        if (declarationDescriptors == null) {
-            declarationDescriptors = ArrayList()
-            labelsToDescriptors.put(name, declarationDescriptors!!)
-        }
-        declarationDescriptors!!.add(descriptor)
+        var declarationDescriptors = labelsToDescriptors.getOrPut(name) { ArrayList() }
+        declarationDescriptors.add(descriptor)
     }
 
     private fun getVariableOrClassDescriptors(): MutableMap<Name, DeclarationDescriptor> {
@@ -125,13 +122,6 @@ public class WritableScopeImpl(override val workerScope: JetScope,
         return variableOrClassDescriptors!!
     }
 
-    private fun getPackageAliases(): MutableMap<Name, PackageViewDescriptor> {
-        if (packageAliases == null) {
-            packageAliases = HashMap()
-        }
-        return packageAliases!!
-    }
-
     override fun addVariableDescriptor(variableDescriptor: VariableDescriptor) {
         addVariableDescriptor(variableDescriptor, false)
     }
@@ -157,17 +147,14 @@ public class WritableScopeImpl(override val workerScope: JetScope,
         checkMayRead()
 
         val propertyGroupsByName = propertyGroups?.get(name) ?: return workerScope.getProperties(name)
-
-        val result = Sets.newLinkedHashSet(propertyGroupsByName)
-        result.addAll(workerScope.getProperties(name))
-        return result
+        return concatInOrder(propertyGroupsByName, workerScope.getProperties(name))
     }
 
     override fun getLocalVariable(name: Name): VariableDescriptor? {
         checkMayRead()
 
-        val descriptor = getVariableOrClassDescriptors()[name]
-        if (descriptor is VariableDescriptor && !getPropertyGroups()[name].contains(descriptor)) {
+        val descriptor = variableOrClassDescriptors?.get(name)
+        if (descriptor is VariableDescriptor && propertyGroups?.get(name)?.contains(descriptor) != true) {
             return descriptor
         }
 
@@ -198,11 +185,8 @@ public class WritableScopeImpl(override val workerScope: JetScope,
     override fun getFunctions(name: Name): Collection<FunctionDescriptor> {
         checkMayRead()
 
-        val functionGroupByName = functionGroups?.get(name) ?: return workerScope.getFunctions(name)
-
-        val result = Sets.newLinkedHashSet(functionGroupByName)
-        result.addAll(workerScope.getFunctions(name))
-        return result
+        val functionGroupByName = functionGroups?.get(name)
+        return concatInOrder(functionGroupByName, workerScope.getFunctions(name))
     }
 
     override fun addClassifierDescriptor(classifierDescriptor: ClassifierDescriptor) {
@@ -238,14 +222,14 @@ public class WritableScopeImpl(override val workerScope: JetScope,
     override fun getClassifier(name: Name): ClassifierDescriptor? {
         checkMayRead()
 
-        return getVariableOrClassDescriptors()[name] as? ClassifierDescriptor
+        return variableOrClassDescriptors?.get(name) as? ClassifierDescriptor
                ?: workerScope.getClassifier(name)
     }
 
     override fun getPackage(name: Name): PackageViewDescriptor? {
         checkMayRead()
 
-        return getPackageAliases().get(name)
+        return packageAliases?.get(name)
                ?: workerScope.getPackage(name)
     }
 

compiler/tests/org/jetbrains/kotlin/jvm/runtime/AbstractJvmRuntimeDescriptorLoaderTest.kt

@@ -161,8 +161,7 @@ public abstract class AbstractJvmRuntimeDescriptorLoaderTest : TestCaseWithTmpdi
 
         // Since runtime package view descriptor doesn't support getAllDescriptors(), we construct a synthetic package view here.
         // It has in its scope descriptors for all the classes and top level members generated by the compiler
-        val actual = SyntheticPackageViewForTest(module, packageScopes, classes)
-        return actual
+        return SyntheticPackageViewForTest(module, packageScopes, classes)
     }
 
     private fun addRuntimeRetentionToKotlinSource(text: String): String {
@@ -188,7 +187,7 @@ public abstract class AbstractJvmRuntimeDescriptorLoaderTest : TestCaseWithTmpdi
             val writableScope = WritableScopeImpl(JetScope.Empty, this, RedeclarationHandler.THROW_EXCEPTION, "runtime descriptor loader test")
             classes.forEach { writableScope.addClassifierDescriptor(it) }
             writableScope.changeLockLevel(WritableScope.LockLevel.READING)
-            scope = ChainedScope(null, "", *(listOf(writableScope) + packageScopes).toTypedArray())
+            scope = ChainedScope(this, "synthetic package view for test", writableScope, *packageScopes.toTypedArray())
         }
 
         override fun getFqName() = LoadDescriptorUtil.TEST_PACKAGE_FQNAME

compiler/tests/org/jetbrains/kotlin/types/JetTypeCheckerTest.java

@@ -625,7 +625,7 @@ public class JetTypeCheckerTest extends JetLiteFixture {
         }
         scopeChain.add(module.getPackage(FqName.ROOT).getMemberScope());
         writableScope.changeLockLevel(WritableScope.LockLevel.BOTH);
-        return new ChainedScope(scope.getContainingDeclaration(), "", scopeChain.toArray(new JetScope[scopeChain.size()]));
+        return new ChainedScope(scope.getContainingDeclaration(), "JetTypeCheckerTest.addImports scope with imports", scopeChain.toArray(new JetScope[scopeChain.size()]));
     }
 
     private JetType makeType(String typeStr) {

core/descriptors/src/org/jetbrains/kotlin/resolve/scopes/ChainedScope.kt

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.resolve.scopes
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.utils.Printer
+import org.jetbrains.kotlin.util.collectionUtils.concat
 import java.util.*
 
 public open class ChainedScope(
@@ -38,15 +39,11 @@ public open class ChainedScope(
         return null
     }
 
-    private inline fun getFromAllScopes<T>(callback: (JetScope) -> Collection<T>): Set<T> {
+    private inline fun getFromAllScopes<T>(callback: (JetScope) -> Collection<T>): Collection<T> {
         if (scopeChain.isEmpty()) return emptySet()
-        var result: MutableSet<T>? = null
+        var result: Collection<T>? = null
         for (scope in scopeChain) {
-            val fromScope = callback(scope)
-            if (result == null) {
-                result = LinkedHashSet<T>()
-            }
-            result.addAll(fromScope)
+            result = result.concat(callback(scope))
         }
         return result ?: emptySet()
     }
@@ -57,13 +54,13 @@ public open class ChainedScope(
     override fun getPackage(name: Name): PackageViewDescriptor?
             = getFirstMatch { it.getPackage(name) }
 
-    override fun getProperties(name: Name): Set<VariableDescriptor>
+    override fun getProperties(name: Name): Collection<VariableDescriptor>
             = getFromAllScopes { it.getProperties(name) }
 
     override fun getLocalVariable(name: Name): VariableDescriptor?
             = getFirstMatch { it.getLocalVariable(name) }
 
-    override fun getFunctions(name: Name): Set<FunctionDescriptor>
+    override fun getFunctions(name: Name): Collection<FunctionDescriptor>
             = getFromAllScopes { it.getFunctions(name) }
 
     override fun getImplicitReceiversHierarchy(): List<ReceiverParameterDescriptor> {

core/descriptors/src/org/jetbrains/kotlin/util/collectionUtils.kt

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.util.collectionUtils
+
+import java.util.*
+
+/**
+ * Concatenates the contents of this collection with the given collection, avoiding allocations if possible.
+ * Can modify `this` if it is a mutable collection.
+ */
+fun <T> Collection<T>?.concat(collection: Collection<T>): Collection<T>? {
+    if (collection.isEmpty()) {
+        return this
+    }
+    if (this == null) {
+        return collection
+    }
+    if (this is LinkedHashSet<*>) {
+        addAll(collection)
+        return this
+    }
+
+    val result = LinkedHashSet(this)
+    result.addAll(collection)
+    return result
+}
+
+fun concatInOrder<T>(c1: Collection<T>?, c2: Collection<T>?): Collection<T> {
+    val result = if (c1 == null || c1.isEmpty())
+        c2
+    else if (c2 == null || c2.isEmpty())
+        c1
+    else {
+        val result = LinkedHashSet<T>()
+        result.addAll(c1)
+        result.addAll(c2)
+        result
+    }
+    return result ?: emptySet()
+}