Fix inheritance from protected members of interfaces

#KT-3029 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/AsmUtil.java

@@ -32,12 +32,12 @@ import org.jetbrains.kotlin.codegen.intrinsics.IntrinsicMethods;
 import org.jetbrains.kotlin.codegen.state.GenerationState;
 import org.jetbrains.kotlin.codegen.state.JetTypeMapper;
 import org.jetbrains.kotlin.descriptors.*;
+import org.jetbrains.kotlin.jvm.RuntimeAssertionInfo;
 import org.jetbrains.kotlin.lexer.JetTokens;
 import org.jetbrains.kotlin.load.java.JavaVisibilities;
 import org.jetbrains.kotlin.load.java.JvmAbi;
 import org.jetbrains.kotlin.load.java.JvmAnnotationNames;
 import org.jetbrains.kotlin.load.java.descriptors.JavaCallableMemberDescriptor;
-import org.jetbrains.kotlin.jvm.RuntimeAssertionInfo;
 import org.jetbrains.kotlin.name.FqName;
 import org.jetbrains.kotlin.resolve.DescriptorUtils;
 import org.jetbrains.kotlin.resolve.annotations.AnnotationsPackage;
@@ -330,13 +330,21 @@ public class AsmUtil {
             PropertyDescriptor property = ((PropertyAccessorDescriptor) memberDescriptor).getCorrespondingProperty();
             if (property instanceof SyntheticJavaPropertyDescriptor) {
                 FunctionDescriptor method = memberDescriptor == property.getGetter()
-                                                ? ((SyntheticJavaPropertyDescriptor) property).getGetMethod()
-                                                : ((SyntheticJavaPropertyDescriptor) property).getSetMethod();
-                assert method != null : "No setMethod in SyntheticJavaPropertyDescriptor";
+                                            ? ((SyntheticJavaPropertyDescriptor) property).getGetMethod()
+                                            : ((SyntheticJavaPropertyDescriptor) property).getSetMethod();
+                assert method != null : "No get/set method in SyntheticJavaPropertyDescriptor: " + property;
                 return getVisibilityAccessFlag(method);
             }
         }
 
+        if (memberDescriptor instanceof CallableDescriptor && memberVisibility == Visibilities.PROTECTED) {
+            for (CallableDescriptor overridden : DescriptorUtils.getAllOverriddenDescriptors((CallableDescriptor) memberDescriptor)) {
+                if (isInterface(overridden.getContainingDeclaration())) {
+                    return ACC_PUBLIC;
+                }
+            }
+        }
+
         if (!Visibilities.isPrivate(memberVisibility)) {
             return null;
         }

compiler/testData/codegen/box/traits/inheritProtectedInterfaceMembers.kt

@@ -0,0 +1,30 @@
+interface A {
+    protected fun foo()
+
+    protected fun fooImpl() { }
+
+    protected var bar: Int
+
+    public var baz: String
+        public get() = ""
+        protected set(value) {}
+
+    fun test(): String {
+        foo()
+        fooImpl()
+        bar = bar + 1
+        baz = baz + "1"
+        return "OK"
+    }
+}
+
+class B : A {
+    protected override fun foo() {}
+
+    protected override var bar: Int = 42
+
+    override var baz: String = ""
+        protected set
+}
+
+fun box() = B().test()

compiler/testData/codegen/box/traits/protectedClassInInterface.kt

@@ -0,0 +1,11 @@
+interface Foo {
+    protected class Bar {
+        fun box() = "OK"
+    }
+}
+
+class Baz : Foo {
+    fun box() = Foo.Bar().box()
+}
+
+fun box() = Baz().box()

compiler/testData/codegen/box/traits/protectedFunDiamond.kt

@@ -0,0 +1,15 @@
+interface A {
+    protected fun foo(): String
+
+    fun box() = foo()
+}
+
+interface B : A
+
+interface C : A {
+    protected override fun foo() = "OK"
+}
+
+class D : B, C
+
+fun box() = D().box()

compiler/tests/org/jetbrains/kotlin/codegen/generated/BlackBoxCodegenTestGenerated.java

@@ -7420,6 +7420,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("inheritProtectedInterfaceMembers.kt")
+        public void testInheritProtectedInterfaceMembers() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/traits/inheritProtectedInterfaceMembers.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("inheritedFun.kt")
         public void testInheritedFun() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/traits/inheritedFun.kt");
@@ -7516,6 +7522,18 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("protectedClassInInterface.kt")
+        public void testProtectedClassInInterface() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/traits/protectedClassInInterface.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("protectedFunDiamond.kt")
+        public void testProtectedFunDiamond() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/traits/protectedFunDiamond.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("traitImplDelegationWithCovariantOverride.kt")
         public void testTraitImplDelegationWithCovariantOverride() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/traits/traitImplDelegationWithCovariantOverride.kt");