Workaround issues with empty titles for some unnamed C symbols (#1100)

* Workaround issues with empty titles for some unnamed C symbols

rdar://139305015

* Extract workaround to private function

* Add another named inner container to new test data

Author: d-ronnqvist

Sources/SwiftDocC/Infrastructure/Symbol Graph/SymbolGraphLoader.swift

@@ -76,6 +76,8 @@ struct SymbolGraphLoader {
                     symbolGraph = try SymbolGraphConcurrentDecoder.decode(data)
                 }
 
+                Self.applyWorkaroundFor139305015(to: &symbolGraph)
+                
                 symbolGraphTransformer?(&symbolGraph)
 
                 let (moduleName, isMainSymbolGraph) = Self.moduleNameFor(symbolGraph, at: symbolGraphURL)
@@ -362,6 +364,62 @@ struct SymbolGraphLoader {
         }
         return (moduleName, isMainSymbolGraph)
     }
+    
+    private static func applyWorkaroundFor139305015(to symbolGraph: inout SymbolGraph) {
+        guard symbolGraph.symbols.values.mapFirst(where: { SourceLanguage(id: $0.identifier.interfaceLanguage) }) == .objectiveC else {
+            return
+        }
+        
+        // Clang emits anonymous structs and unions differently than anonymous enums (rdar://139305015).
+        //
+        // The anonymous structs, with empty names, causes issues in a few different places for DocC:
+        // - The IndexingRecords (one of the `--emit-digest` files) throws an error about the empty name.
+        // - The NavigatorIndex.Builder may throw an error about the empty name.
+        // - Their pages can't be navigated to because their URL path end with a leading slash.
+        //   The corresponding static hosting 'index.html' copy also overrides the container's index.html file because
+        //   its file path has two slashes, for example "/documentation/ModuleName/ContainerName//index.html".
+        //
+        // To avoid all those issues without handling empty names throughout the code,
+        // we fill in titles and navigator titles for these symbols using the same format as Clang uses for anonymous enums.
+        
+        let relationshipsByTarget = [String: [SymbolGraph.Relationship]](grouping: symbolGraph.relationships, by: \.target)
+        
+        for (usr, symbol) in symbolGraph.symbols {
+            guard symbol.names.title.isEmpty,
+                  symbol.names.navigator?.map(\.spelling).joined().isEmpty == true,
+                  symbol.pathComponents.last?.isEmpty == true
+            else {
+                continue
+            }
+            
+            // This symbol has an empty title and an empty navigator title.
+            var modified = symbol
+            let fallbackTitle = "\(symbol.kind.identifier.identifier) (unnamed)"
+            modified.names.title = fallbackTitle
+            // Clang uses a single `identifier` fragment for anonymous enums.
+            modified.names.navigator = [.init(kind: .identifier, spelling: fallbackTitle, preciseIdentifier: nil)]
+            // Don't update `modified.names.subHeading`. Clang _doesn't_ use "enum (unnamed)" for the `Symbol/Names/subHeading` so we don't add it here either.
+            
+            // Clang uses the "enum (unnamed)" in the path components of anonymous enums so we follow that format for anonymous structs.
+            modified.pathComponents[modified.pathComponents.count - 1] = fallbackTitle
+            symbolGraph.symbols[usr] = modified
+            
+            // Also update all the members whose path components start with the container's path components so that they're consistent.
+            if let relationships = relationshipsByTarget[usr] {
+                let containerPathComponents = modified.pathComponents
+                
+                for memberRelationship in relationships where memberRelationship.kind == .memberOf {
+                    guard var modifiedMember = symbolGraph.symbols.removeValue(forKey: memberRelationship.source) else { continue }
+                    // Only update the member's path components if it starts with the original container's components.
+                    guard modifiedMember.pathComponents.starts(with: symbol.pathComponents) else { continue }
+                    
+                    modifiedMember.pathComponents.replaceSubrange(containerPathComponents.indices, with: containerPathComponents)
+                    
+                    symbolGraph.symbols[memberRelationship.source] = modifiedMember
+                }
+            }
+        }
+    }
 }
 
 extension SymbolGraph.SemanticVersion {

Sources/SwiftDocCTestUtilities/SymbolGraphCreation.swift

@@ -104,7 +104,7 @@ extension XCTestCase {
 
         return SymbolGraph.Symbol(
             identifier: SymbolGraph.Symbol.Identifier(precise: id, interfaceLanguage: language.id),
-            names: makeSymbolNames(name: pathComponents.first!),
+            names: makeSymbolNames(name: pathComponents.last!),
             pathComponents: pathComponents,
             docComment: docComment.map {
                 makeLineList(

Tests/SwiftDocCTests/Model/SemaToRenderNodeTests.swift

@@ -3605,4 +3605,45 @@ Document
 
         XCTAssertEqual(expectedContent, renderContent)
     }
+    
+    func testSymbolWithEmptyName() throws {
+        // Symbols _should_ have names, but due to bugs there's cases when anonymous C structs don't.
+        let catalog = Folder(name: "unit-test.docc", content: [
+            JSONFile(name: "ModuleName.symbols.json", content: makeSymbolGraph(
+                moduleName: "ModuleName",
+                symbols: [
+                    makeSymbol(id: "some-container",      language: .objectiveC, kind: .class,  pathComponents: ["SomeContainer"]),
+                    makeSymbol(id: "some-unnamed-struct", language: .objectiveC, kind: .struct, pathComponents: ["SomeContainer", ""]),
+                    makeSymbol(id: "some-inner-member",   language: .objectiveC, kind: .var,    pathComponents: ["SomeContainer", "", "someMember"]),
+                    
+                    makeSymbol(id: "some-named-struct",   language: .objectiveC, kind: .struct, pathComponents: ["SomeContainer", "NamedInnerContainer"]),
+                ],
+                relationships: [
+                    .init(source: "some-unnamed-struct", target: "some-container",      kind: .memberOf, targetFallback: nil),
+                    .init(source: "some-inner-member",   target: "some-unnamed-struct", kind: .memberOf, targetFallback: nil),
+                    
+                    .init(source: "some-named-struct",   target: "some-container",      kind: .memberOf, targetFallback: nil),
+                ]
+            ))
+        ])
+        
+        let (bundle, context) = try loadBundle(catalog: catalog)
+        
+        XCTAssertEqual(context.knownPages.map(\.path).sorted(), [
+            "/documentation/ModuleName",
+            "/documentation/ModuleName/SomeContainer",
+            "/documentation/ModuleName/SomeContainer/NamedInnerContainer",
+            "/documentation/ModuleName/SomeContainer/struct_(unnamed)",
+            "/documentation/ModuleName/SomeContainer/struct_(unnamed)/someMember"
+        ], "The reference paths shouldn't have any empty components")
+        
+        let unnamedStructReference = try XCTUnwrap(context.soleRootModuleReference).appendingPath("SomeContainer/struct_(unnamed)")
+        let node = try context.entity(with: unnamedStructReference)
+        
+        let converter = DocumentationNodeConverter(bundle: bundle, context: context)
+        let renderNode = try converter.convert(node)
+        
+        XCTAssertEqual(renderNode.metadata.title, "struct (unnamed)")
+        XCTAssertEqual(renderNode.metadata.navigatorTitle?.map(\.text).joined(), "struct (unnamed)")
+    }
 }