Fix a doc anchor is not encoded correctly

Sources/SwiftDocC/Infrastructure/NodeURLGenerator.swift

@@ -171,7 +171,7 @@ public struct NodeURLGenerator {
             )
         } else {
             let url = baseURL.appendingPathComponent(safePath, isDirectory: false)
-            return url.withFragment(reference.url.fragment)
+            return url.withFragment(reference.url.fragment?.removingPercentEncoding)
         }
     }
 

Sources/SwiftDocC/Model/Rendering/RenderContentCompiler.swift

@@ -46,7 +46,11 @@ struct RenderContentCompiler: MarkupVisitor {
     }
 
     mutating func visitHeading(_ heading: Heading) -> [RenderContent] {
-        return [RenderBlockContent.heading(.init(level: heading.level, text: heading.plainText, anchor: urlReadableFragment(heading.plainText)))]
+        let fragment = urlReadableFragment(heading.plainText)
+        var components = URLComponents()
+        components.fragment = fragment
+        let anchor = components.url?.fragment ?? fragment
+        return [RenderBlockContent.heading(.init(level: heading.level, text: heading.plainText, anchor: anchor))]
     }
 
     mutating func visitListItem(_ listItem: ListItem) -> [RenderContent] {

Tests/SwiftDocCTests/Infrastructure/NodeURLGeneratorTests.swift

@@ -77,6 +77,19 @@ class NodeURLGeneratorTests: XCTestCase {
         XCTAssertEqual(generator.urlForReference(classIdentifier).absoluteString, "file:///path/to/bundle/_testbundle-ctlj/products/documentation.builtbundle/com.example.testbundle/data/folder/_privateclass/_privatesubclass")
     }
 
+    func testsafeURLWithEncodableFragment() throws {
+        // This is a realist DerivedData folder.
+        let baseURL = URL(string: "file:///path/to/bundle/_testbundle-ctlj/products/documentation.builtbundle/com.example.testbundle/data/")!
+        let generator = NodeURLGenerator(baseURL: baseURL)
+
+        let basicIdentifier = ResolvedTopicReference(bundleIdentifier: "com.example.testbundle",
+                                                     path: "/folder/class/symbol",
+                                                     fragment: "テスト", // Non-ASCII; E3 83 86 E3 82 B9 E3 83 88 in UTF-8
+                                                     sourceLanguage: .swift)
+
+        XCTAssertEqual(generator.urlForReference(basicIdentifier).absoluteString, "file:///path/to/bundle/_testbundle-ctlj/products/documentation.builtbundle/com.example.testbundle/data/folder/class/symbol#%E3%83%86%E3%82%B9%E3%83%88")
+    }
+
     var inputLongPaths = [
         // Paths within the limits
         "/path/to/symbol.json",

Tests/SwiftDocCTests/Model/RenderContentMetadataTests.swift

@@ -297,4 +297,26 @@ class RenderContentMetadataTests: XCTestCase {
             default: XCTFail("Unexpected element")
         }
     }
+
+    func testHeadingAnchorShouldBeEncoded() throws {
+        let (bundle, context) = try testBundleAndContext(named: "TestBundle")
+        var renderContentCompiler = RenderContentCompiler(context: context, bundle: bundle, identifier: ResolvedTopicReference(bundleIdentifier: bundle.identifier, path: "/path", fragment: nil, sourceLanguage: .swift))
+
+        let source = """
+        ## テスト
+
+        Note that テスト consists of Non-ASCII characters of E3 83 86 E3 82 B9 E3 83 88 in UTF-8.
+        """
+        let document = Document(parsing: source)
+
+        let result = try XCTUnwrap(renderContentCompiler.visit(document.child(at: 0)!))
+        let element = try XCTUnwrap(result.first as? RenderBlockContent)
+        switch element {
+        case .heading(let heading):
+            XCTAssertEqual(heading.level, 2)
+            XCTAssertEqual(heading.text, "テスト")
+            XCTAssertEqual(heading.anchor, "%E3%83%86%E3%82%B9%E3%83%88")
+        default: XCTFail("Unexpected element")
+        }
+    }
 }