Fir2Ir: provide fake file-level signatures for toplevel privates

We need to supply signatures for private declarations even when their
containing file is not known. In situations where the FirDeclaration in
question is already known (i.e. where we are never going to serach for
the declaation based on that signature), FirDeclaration itself is
sufficient as a key.

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

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.fir.declarations.utils.visibility
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTag
 import org.jetbrains.kotlin.fir.visitors.FirVisitor
 import org.jetbrains.kotlin.ir.util.IdSignature
+import org.jetbrains.kotlin.name.FqName
 
 // @NoMutableState -- we'll restore this annotation once we get rid of withFileSignature().
 class FirBasedSignatureComposer(override val mangler: FirMangler) : Fir2IrSignatureComposer {
@@ -122,7 +123,7 @@ class FirBasedSignatureComposer(override val mangler: FirMangler) : Fir2IrSignat
             else -> error("Unsupported FIR declaration in signature composer: ${declaration.render()}")
         }
         return if (isTopLevelPrivate(declaration) || forceTopLevelPrivate) {
-            val fileSig = fileSignature ?: return null
+            val fileSig = fileSignature ?: declaration.fakeFileSignature(publicSignature)
             IdSignature.CompositeSignature(fileSig, publicSignature)
         } else
             publicSignature
@@ -181,6 +182,13 @@ class FirBasedSignatureComposer(override val mangler: FirMangler) : Fir2IrSignat
     private fun isTopLevelPrivate(declaration: FirDeclaration): Boolean =
         declaration.symbol.getOwnerLookupTag() == null && declaration is FirMemberDeclaration && declaration.visibility == Visibilities.Private
 
+    // We only need file signatures to distinguish between declarations with the same fqName across different files,
+    // so FirDeclaration itself is an appropriate id.
+    private fun FirDeclaration.fakeFileSignature(commonSignature: IdSignature.CommonSignature) =
+        IdSignature.FileSignature(
+            this, FqName(commonSignature.packageFqName + "." + commonSignature.declarationFqName), "<unknown>"
+        )
+
     private fun FirProperty.getterOrDefault() =
         getter ?: FirDefaultPropertyGetter(
             source = null,

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java

@@ -7415,6 +7415,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
         }
 
+        @Test
+        @TestMetadata("privateSuperType.kt")
+        public void testPrivateSuperType() throws Exception {
+            runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+        }
+
         @Test
         @TestMetadata("propertyReference.kt")
         public void testPropertyReference() throws Exception {

compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt

@@ -0,0 +1,19 @@
+// MODULE: lib
+// FILE: Z.kt
+package z
+
+private interface I {
+     fun k() = "K"
+}
+
+interface G<T>
+
+class Z : I, G<I> {
+    val o = "O"
+}
+
+// MODULE: main(lib)
+// FILE: box.kt
+import z.Z
+
+fun box() = Z().run { o + k() }

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java

@@ -7301,6 +7301,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
         }
 
+        @Test
+        @TestMetadata("privateSuperType.kt")
+        public void testPrivateSuperType() throws Exception {
+            runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+        }
+
         @Test
         @TestMetadata("propertyReference.kt")
         public void testPropertyReference() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java

@@ -7415,6 +7415,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
         }
 
+        @Test
+        @TestMetadata("privateSuperType.kt")
+        public void testPrivateSuperType() throws Exception {
+            runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+        }
+
         @Test
         @TestMetadata("propertyReference.kt")
         public void testPropertyReference() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmIrAgainstOldBoxTestGenerated.java

@@ -397,6 +397,12 @@ public class JvmIrAgainstOldBoxTestGenerated extends AbstractJvmIrAgainstOldBoxT
         runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
     }
 
+    @Test
+    @TestMetadata("privateSuperType.kt")
+    public void testPrivateSuperType() throws Exception {
+        runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+    }
+
     @Test
     @TestMetadata("propertyReference.kt")
     public void testPropertyReference() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmOldAgainstIrBoxTestGenerated.java

@@ -397,6 +397,12 @@ public class JvmOldAgainstIrBoxTestGenerated extends AbstractJvmOldAgainstIrBoxT
         runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
     }
 
+    @Test
+    @TestMetadata("privateSuperType.kt")
+    public void testPrivateSuperType() throws Exception {
+        runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+    }
+
     @Test
     @TestMetadata("propertyReference.kt")
     public void testPropertyReference() throws Exception {

native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java

@@ -5605,6 +5605,12 @@ public class NativeCodegenBoxTestGenerated extends AbstractNativeCodegenBoxTest
                 runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/nestedTypeAliasExpansion.kt");
             }
 
+            @Test
+            @TestMetadata("privateSuperType.kt")
+            public void testPrivateSuperType() throws Exception {
+                runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+            }
+
             @Test
             @TestMetadata("propertyReference.kt")
             public void testPropertyReference() throws Exception {