[FIR2IR] Introduce & use FirBuiltInsPackageFragment

Without this commit, JVM name mapping logic in BE does not work for FIR,
because FIR cannot use old BuiltInsPackageFragmentImpl descriptor.
In this commit we add our own implementation thus fixing
a pack of FIR black box tests.

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrDeclarationStorage.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.fir.backend
 
 import org.jetbrains.kotlin.KtNodeTypes
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns.*
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.SourceElement
@@ -14,6 +15,7 @@ import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertyGetter
 import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertySetter
+import org.jetbrains.kotlin.fir.descriptors.FirBuiltInsPackageFragment
 import org.jetbrains.kotlin.fir.descriptors.FirModuleDescriptor
 import org.jetbrains.kotlin.fir.descriptors.FirPackageFragmentDescriptor
 import org.jetbrains.kotlin.fir.expressions.impl.FirExpressionStub
@@ -54,6 +56,8 @@ class Fir2IrDeclarationStorage(
 
     private val fragmentCache = mutableMapOf<FqName, IrExternalPackageFragment>()
 
+    private val builtInsFragmentCache = mutableMapOf<FqName, IrExternalPackageFragment>()
+
     private val fileCache = mutableMapOf<FirFile, IrFile>()
 
     private val functionCache = mutableMapOf<FirFunction<*>, IrSimpleFunction>()
@@ -110,9 +114,19 @@ class Fir2IrDeclarationStorage(
     private fun ConeKotlinType.toIrType(typeContext: ConversionTypeContext = ConversionTypeContext.DEFAULT): IrType =
         with(typeConverter) { toIrType(typeContext) }
 
+    private fun getIrExternalOrBuiltInsPackageFragment(fqName: FqName): IrExternalPackageFragment {
+        val isBuiltIn = fqName in BUILT_INS_PACKAGE_FQ_NAMES
+        return if (isBuiltIn) getIrBuiltInsPackageFragment(fqName) else getIrExternalPackageFragment(fqName)
+    }
+
+    private fun getIrBuiltInsPackageFragment(fqName: FqName): IrExternalPackageFragment {
+        return builtInsFragmentCache.getOrPut(fqName) {
+            return symbolTable.declareExternalPackageFragment(FirBuiltInsPackageFragment(fqName, moduleDescriptor))
+        }
+    }
+
     private fun getIrExternalPackageFragment(fqName: FqName): IrExternalPackageFragment {
         return fragmentCache.getOrPut(fqName) {
-            // TODO: module descriptor is wrong here
             return symbolTable.declareExternalPackageFragment(FirPackageFragmentDescriptor(fqName, moduleDescriptor))
         }
     }
@@ -187,10 +201,12 @@ class Fir2IrDeclarationStorage(
                 else -> throw AssertionError("Unexpected: $firBasedSymbol")
             }
 
-            if (containerFile != null) {
-                fileCache[containerFile]
-            } else {
-                getIrExternalPackageFragment(packageFqName)
+            when {
+                containerFile != null -> fileCache[containerFile]
+                firBasedSymbol is FirCallableSymbol -> getIrExternalPackageFragment(packageFqName)
+                // TODO: All classes from BUILT_INS_PACKAGE_FQ_NAMES are considered built-ins now,
+                // which is not exact and can lead to some problems
+                else -> getIrExternalOrBuiltInsPackageFragment(packageFqName)
             }
         }
     }

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/descriptors/FirBuiltInsPackageFragment.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2010-2020 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.fir.descriptors
+
+import org.jetbrains.kotlin.builtins.BuiltInsPackageFragment
+import org.jetbrains.kotlin.descriptors.ModuleDescriptor
+import org.jetbrains.kotlin.name.FqName
+
+class FirBuiltInsPackageFragment(
+    fqName: FqName,
+    moduleDescriptor: ModuleDescriptor
+) : FirPackageFragmentDescriptor(fqName, moduleDescriptor), BuiltInsPackageFragment {
+    override val isFallback: Boolean
+        get() = false
+}

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/descriptors/FirPackageFragmentDescriptor.kt

@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
 
-class FirPackageFragmentDescriptor(override val fqName: FqName, val moduleDescriptor: ModuleDescriptor) : PackageFragmentDescriptor {
+open class FirPackageFragmentDescriptor(override val fqName: FqName, val moduleDescriptor: ModuleDescriptor) : PackageFragmentDescriptor {
     override fun getContainingDeclaration(): ModuleDescriptor {
         return moduleDescriptor
     }