Regression - private subclasses showing

Sources/SwiftDoc/Interface.swift

@@ -15,10 +15,12 @@ public final class Interface {
         self.topLevelSymbols = symbols.filter { $0.api is Type || $0.id.pathComponents.isEmpty }
 
         self.relationships = {
+            let symbols = symbols.filter { $0.isPublic }
             let extensionsByExtendedType: [String: [Extension]] = Dictionary(grouping: symbols.flatMap { $0.context.compactMap { $0 as? Extension } }, by: { $0.extendedType })
 
             var relationships: Set<Relationship> = []
             for symbol in symbols {
+
                 let lastDeclarationScope = symbol.context.last(where: { $0 is Extension || $0 is Symbol })
 
                 if let container = lastDeclarationScope as? Symbol {

Tests/SwiftDocTests/InterfaceTypeTests.swift

@@ -0,0 +1,41 @@
+import XCTest
+
+import SwiftDoc
+import SwiftSemantics
+import struct SwiftSemantics.Protocol
+import SwiftSyntax
+
+final class InterfaceTypeTests: XCTestCase {
+
+    func testPrivateInheritance() throws {
+        let source = #"""
+        public class A { }
+
+        class B : A { }
+
+        public class C : A { }
+        """#
+
+        let url = try temporaryFile(contents: source)
+        let sourceFile = try SourceFile(file: url, relativeTo: url.deletingLastPathComponent())
+        let module = Module(name: "Module", sourceFiles: [sourceFile])
+
+        // `class A`
+        let classA = sourceFile.symbols[0]
+        XCTAssert(classA.api is Class)
+
+         // `class B`
+        let classB = sourceFile.symbols[1]
+        XCTAssert(classB.api is Class)
+
+        // `class C`
+        let classC = sourceFile.symbols[2]
+        XCTAssert(classC.api is Class)
+
+        // Class B does not exist in subclasses because it's not public
+        // Class C exists in subclasses because it's public
+        let subclasses = module.interface.typesInheriting(from: classA)
+        XCTAssertEqual(subclasses.count, 1)
+        XCTAssertEqual(subclasses[0].id, classC.id)
+    }
+}