FIR: temporary implementation of kotlin.FunctionX resolve

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/impl/FirLibrarySymbolProviderImpl.kt

@@ -6,12 +6,14 @@
 package org.jetbrains.kotlin.fir.resolve.impl
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.builtins.functions.FunctionClassDescriptor
 import org.jetbrains.kotlin.descriptors.SourceElement
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.deserialization.FirTypeDeserializer
 import org.jetbrains.kotlin.fir.resolve.FirSymbolProvider
 import org.jetbrains.kotlin.fir.symbols.ConeSymbol
 import org.jetbrains.kotlin.fir.symbols.LibraryClassSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.builtins.BuiltInsBinaryVersion
 import org.jetbrains.kotlin.metadata.deserialization.NameResolverImpl
@@ -92,8 +94,20 @@ class FirLibrarySymbolProviderImpl(val session: FirSession) : FirSymbolProvider
 
     private val allPackageFragments = loadBuiltIns().groupBy { it.fqName }
 
+    private val fictitiousFunctionSymbols = mutableMapOf<Int, ConeSymbol>()
+
     override fun getSymbolByFqName(classId: ClassId): ConeSymbol? {
-        return allPackageFragments[classId.packageFqName]?.firstNotNullResult { it.getSymbolByFqName(classId, this) }
+        return allPackageFragments[classId.packageFqName]?.firstNotNullResult {
+            it.getSymbolByFqName(classId, this)
+        } ?: with(classId) {
+            val className = relativeClassName.asString()
+            val kind = FunctionClassDescriptor.Kind.byClassNamePrefix(packageFqName, className) ?: return@with null
+            val prefix = kind.classNamePrefix
+            val arity = className.substring(prefix.length).toIntOrNull() ?: return null
+            fictitiousFunctionSymbols.getOrPut(arity) {
+                FirClassSymbol(classId)
+            }
+        }
     }
 
 }

compiler/testData/fir/resolve/stdlib/functionX.kt

@@ -0,0 +1,5 @@
+import kotlin.jvm.functions.Function0
+
+val x: Function0<Int> = { 42 }
+
+val y: Function1<String, String> = { it }

compiler/testData/fir/resolve/stdlib/functionX.txt

@@ -0,0 +1,5 @@
+FILE: functionX.kt
+    public? final? property x(val): R|kotlin/jvm/functions/Function0<kotlin/Int>| = STUB
+        public? get(): R|kotlin/jvm/functions/Function0<kotlin/Int>|
+    public? final? property y(val): R|kotlin/Function1<kotlin/String, kotlin/String>| = STUB
+        public? get(): R|kotlin/Function1<kotlin/String, kotlin/String>|

compiler/tests/org/jetbrains/kotlin/fir/FirResolveTestCaseGenerated.java

@@ -31,8 +31,7 @@ public class FirResolveTestCaseGenerated extends AbstractFirResolveTestCase {
 
     @TestMetadata("companion.kt")
     public void testCompanion() throws Exception {
-        String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/fir/resolve/companion.kt");
-        doTest(fileName);
+        runTest("compiler/testData/fir/resolve/companion.kt");
     }
 
     @TestMetadata("derivedClass.kt")

compiler/tests/org/jetbrains/kotlin/fir/FirResolveTestCaseWithStdlibGenerated.java

@@ -34,6 +34,11 @@ public class FirResolveTestCaseWithStdlibGenerated extends AbstractFirResolveTes
         runTest("compiler/testData/fir/resolve/stdlib/concurrent.kt");
     }
 
+    @TestMetadata("functionX.kt")
+    public void testFunctionX() throws Exception {
+        runTest("compiler/testData/fir/resolve/stdlib/functionX.kt");
+    }
+
     @TestMetadata("reflectionClass.kt")
     public void testReflectionClass() throws Exception {
         runTest("compiler/testData/fir/resolve/stdlib/reflectionClass.kt");