[FIR2IR] Add primitive signature composer & use it for external classes

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt

@@ -354,6 +354,14 @@ class Fir2IrClassifierStorage(
         if (firClass is FirAnonymousObject || firClass is FirRegularClass && firClass.visibility == Visibilities.LOCAL) {
             return createIrClass(firClass).symbol
         }
+        val signature = signatureComposer.composeSignature(firClass)
+        symbolTable.referenceClassIfAny(signature)?.let { irClassSymbol ->
+            val irClass = irClassSymbol.owner
+            classCache[firClass as FirRegularClass] = irClass
+            processClassHeader(firClass, irClass)
+            declarationStorage.preCacheBuiltinClassMembers(firClass, irClass)
+            return irClassSymbol
+        }
         // TODO: remove all this code and change to unbound symbol creation
         val classId = firClassSymbol.classId
         val parentId = classId.outerClassId

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrComponents.kt

@@ -18,4 +18,5 @@ interface Fir2IrComponents {
     val classifierStorage: Fir2IrClassifierStorage
     val declarationStorage: Fir2IrDeclarationStorage
     val typeConverter: Fir2IrTypeConverter
+    val signatureComposer: Fir2IrSignatureComposer
 }

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrComponentsStorage.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.fir.backend
 
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.resolve.ScopeSession
+import org.jetbrains.kotlin.fir.signaturer.FirBasedSignatureComposer
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.util.SymbolTable
 
@@ -19,4 +20,6 @@ class Fir2IrComponentsStorage(
     override lateinit var classifierStorage: Fir2IrClassifierStorage
     override lateinit var declarationStorage: Fir2IrDeclarationStorage
     override lateinit var typeConverter: Fir2IrTypeConverter
+
+    override val signatureComposer = FirBasedSignatureComposer()
 }

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrSignatureComposer.kt

@@ -0,0 +1,13 @@
+/*
+ * 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.backend
+
+import org.jetbrains.kotlin.fir.declarations.FirDeclaration
+import org.jetbrains.kotlin.ir.util.IdSignature
+
+interface Fir2IrSignatureComposer {
+    fun composeSignature(declaration: FirDeclaration): IdSignature
+}

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt

@@ -0,0 +1,45 @@
+/*
+ * 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.signaturer
+
+import org.jetbrains.kotlin.descriptors.Visibilities
+import org.jetbrains.kotlin.fir.FirElement
+import org.jetbrains.kotlin.fir.backend.Fir2IrSignatureComposer
+import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.render
+import org.jetbrains.kotlin.fir.visitors.FirVisitorVoid
+import org.jetbrains.kotlin.ir.util.IdSignature
+
+class FirBasedSignatureComposer : Fir2IrSignatureComposer {
+
+    class SignatureBuilder : FirVisitorVoid() {
+        var hashId: Long? = null
+        var mask = 0L
+
+        private fun setExpected(f: Boolean) {
+            mask = mask or IdSignature.Flags.IS_EXPECT.encode(f)
+        }
+
+        override fun visitElement(element: FirElement) {
+            TODO("Not yet implemented")
+        }
+
+        override fun visitRegularClass(regularClass: FirRegularClass) {
+            setExpected(regularClass.isExpect)
+            //platformSpecificClass(descriptor)
+        }
+    }
+
+    override fun composeSignature(declaration: FirDeclaration): IdSignature {
+        val builder = SignatureBuilder()
+        declaration.accept(builder)
+        if (declaration is FirRegularClass && declaration.visibility != Visibilities.LOCAL) {
+            val classId = declaration.classId
+            return IdSignature.PublicSignature(classId.packageFqName, classId.relativeClassName, builder.hashId, builder.mask)
+        }
+        throw AssertionError("Unsupported FIR declaration in signature composer: ${declaration.render()}")
+    }
+}