Add test for soon to be deprecated 'class object' syntax

compiler/testData/diagnostics/tests/classObjects/deprecatedClassObjectSyntax.kt

@@ -0,0 +1,28 @@
+trait G
+
+class A {
+    class object A {
+
+    }
+}
+
+trait B {
+    class object : G {
+
+    }
+}
+
+fun main() {
+    A
+    A.A
+    g(B.Default)
+    g(B)
+
+    A.ext()
+    A.A.ext()
+}
+
+fun g(g: G) { <!UNUSED_EXPRESSION!>g<!> }
+
+fun A.A.ext() {
+}

compiler/testData/diagnostics/tests/classObjects/deprecatedClassObjectSyntax.txt

@@ -0,0 +1,38 @@
+package
+
+internal fun g(/*0*/ g: G): kotlin.Unit
+internal fun main(): kotlin.Unit
+internal fun A.A.ext(): kotlin.Unit
+
+internal final class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    internal default object A {
+        private constructor A()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+internal trait B {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    internal default object Default : G {
+        private constructor Default()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+internal trait G {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}