Fix public extensions exposing nested code of all access levels

Sources/SwiftDoc/Symbol.swift

@@ -43,7 +43,11 @@ public final class Symbol {
 
         if let `extension` = `extension`,
             `extension`.modifiers.contains(where: { $0.name == "public" }) {
-            return true
+
+            let isNotLimitedAccessModifier = { (modifier: Modifier) in
+                modifier.name != "internal" && modifier.name != "fileprivate" && modifier.name != "private"
+            }
+            return api.modifiers.allSatisfy(isNotLimitedAccessModifier)
         }
 
         if let symbol = context.compactMap({ $0 as? Symbol }).last,

Tests/SwiftDocTests/InterfaceTypeTests.swift

@@ -69,4 +69,68 @@ final class InterfaceTypeTests: XCTestCase {
             XCTAssertEqual(symbol.api.name, "A")
         }
     }
+
+    func testFunctionsInPublicExtension() throws {
+        let source = #"""
+        public extension Int {
+            func a() {}
+            public func b() {}
+            internal func c() {}
+            fileprivate func d() {}
+            private func e() {}
+        }
+        """#
+
+        let url = try temporaryFile(contents: source)
+        let sourceFile = try SourceFile(file: url, relativeTo: url.deletingLastPathComponent())
+        let module = Module(name: "Module", sourceFiles: [sourceFile])
+
+        XCTAssertEqual(sourceFile.symbols.count, 5)
+        XCTAssertTrue(sourceFile.symbols[0].isPublic, "Function `a()` should BE marked as public - its visibility is specified by extension")
+        XCTAssertTrue(sourceFile.symbols[1].isPublic, "Function `b()` should BE marked as public - its visibility is public")
+        XCTAssertFalse(sourceFile.symbols[2].isPublic, "Function `c()` should NOT be marked as public - its visibility is internal")
+        XCTAssertFalse(sourceFile.symbols[3].isPublic, "Function `d()` should NOT be marked as public - its visibility is fileprivate")
+        XCTAssertFalse(sourceFile.symbols[4].isPublic, "Function `e()` should NOT be marked as public - its visibility is private")
+
+        XCTAssertEqual(module.interface.symbols.count, 2)
+        XCTAssertEqual(module.interface.symbols[0].name, "a()", "Function `a()` should be in documented interface")
+        XCTAssertEqual(module.interface.symbols[1].name, "b()", "Function `b()` should be in documented interface")
+    }
+
+    func testNestedPropertiesInPublicExtension() throws {
+        let source = #"""
+        public class RootController {}
+
+        public extension RootController {
+            class ControllerExtension {
+                public var public_properties: ExtendedProperties = ExtendedProperties()
+                internal var internal_properties: InternalProperties = InternalProperties()
+            }
+        }
+
+        public extension RootController.ControllerExtension {
+            struct ExtendedProperties {
+                public var public_prop: Int = 1
+            }
+        }
+
+        internal extension RootController.ControllerExtension {
+            struct InternalProperties {
+                internal var internal_prop: String = "FOO"
+            }
+        }
+        """#
+
+
+        let url = try temporaryFile(contents: source)
+        let sourceFile = try SourceFile(file: url, relativeTo: url.deletingLastPathComponent())
+        let module = Module(name: "Module", sourceFiles: [sourceFile])
+
+        XCTAssertEqual(module.interface.symbols.count, 5)
+        XCTAssertEqual(module.interface.symbols[0].name, "RootController")
+        XCTAssertEqual(module.interface.symbols[1].name, "ControllerExtension")
+        XCTAssertEqual(module.interface.symbols[2].name, "public_properties")
+        XCTAssertEqual(module.interface.symbols[3].name, "ExtendedProperties")
+        XCTAssertEqual(module.interface.symbols[4].name, "public_prop")
+    }
 }