Also document default implementations of protocols.

Sources/SwiftDoc/Interface.swift

@@ -155,4 +155,8 @@ public final class Interface {
     public func conditionalCounterparts(of symbol: Symbol) -> [Symbol] {
         return symbolsGroupedByIdentifier[symbol.id]?.filter { $0 != symbol }.sorted() ?? []
     }
+
+    public func defaultImplementations(of symbol: Symbol) -> [Symbol] {
+        return relationshipsByObject[symbol.id]?.filter { $0.predicate == .defaultImplementationOf }.map { $0.subject }.sorted() ?? []
+    }
 }

Sources/swift-doc/Supporting Types/Components/Members.swift

@@ -17,6 +17,7 @@ struct Members: Component {
     var properties: [Symbol]
     var methods: [Symbol]
     var genericallyConstrainedMembers: [[GenericRequirement] : [Symbol]]
+    let defaultImplementations: [Symbol]
 
     init(of symbol: Symbol, in module: Module, baseURL: String, symbolFilter: (Symbol) -> Bool) {
         self.symbol = symbol
@@ -33,6 +34,7 @@ struct Members: Component {
         self.properties = members.filter { $0.api is Variable }
         self.methods = members.filter { $0.api is Function }
         self.genericallyConstrainedMembers = Dictionary(grouping: members) { $0.`extension`?.genericRequirements ?? [] }.filter { !$0.key.isEmpty }
+        self.defaultImplementations = module.interface.defaultImplementations(of: symbol).filter(symbolFilter)
     }
 
     var sections: [(title: String, members: [Symbol])] {
@@ -41,14 +43,15 @@ struct Members: Component {
             ("Initializers", initializers),
             ("Enumeration Cases", cases),
             ("Properties", properties),
-            ("Methods", methods)
+            ("Methods", methods),
+            ("Default Implementations", defaultImplementations),
         ].filter { !$0.members.isEmpty }
     }
 
     // MARK: - Component
 
     var fragment: Fragment {
-        guard !members.isEmpty else { return Fragment { "" } }
+        guard !members.isEmpty || !defaultImplementations.isEmpty else { return Fragment { "" } }
 
         return Fragment {
             ForEach(in: sections) { section -> BlockConvertible in

Tests/SwiftDocTests/InterfaceTypeTests.swift

@@ -240,4 +240,30 @@ final class InterfaceTypeTests: XCTestCase {
         XCTAssertEqual(module.interface.symbols[6].name, "InternalProperties")
         XCTAssertEqual(module.interface.symbols[7].name, "internal_prop")
     }
+
+    func testDefaultImplementationsOfProtocols() throws {
+        let source = #"""
+        public protocol SomeProtocol {
+            func someMethod()
+        }
+
+        public extension SomeProtocol {
+            func someMethod() { }
+
+            func someOtherMethod() { }
+        }
+        """#
+
+
+        let url = try temporaryFile(contents: source)
+        let sourceFile = try SourceFile(file: url, relativeTo: url.deletingLastPathComponent())
+        let module = Module(name: "Module", sourceFiles: [sourceFile])
+
+        let protocolSymbol = module.interface.symbols[0]
+        XCTAssertEqual(protocolSymbol.name, "SomeProtocol")
+        let defaultImplementations = module.interface.defaultImplementations(of: protocolSymbol)
+        XCTAssertEqual(defaultImplementations.count, 2)
+        XCTAssertEqual(defaultImplementations[0].name, "someMethod()")
+        XCTAssertEqual(defaultImplementations[1].name, "someOtherMethod()")
+    }
 }