[clangd] Oops, switchSourceHeader still needs to return a URI.

clangd/ClangdLSPServer.h

private:
   void onSignatureHelp(const TextDocumentPositionParams &,
                        Callback<SignatureHelp>);
   void onGoToDeclaration(const TextDocumentPositionParams &,
                          Callback<std::vector<Location>>);
   void onGoToDefinition(const TextDocumentPositionParams &,
                         Callback<std::vector<Location>>);
   void onReference(const ReferenceParams &, Callback<std::vector<Location>>);
   void onSwitchSourceHeader(const TextDocumentIdentifier &,
-                            Callback<llvm::Optional<std::string>>);
+                            Callback<llvm::Optional<URIForFile>>);
   void onDocumentHighlight(const TextDocumentPositionParams &,
                            Callback<std::vector<DocumentHighlight>>);
   void onFileEvent(const DidChangeWatchedFilesParams &);
   void onCommand(const ExecuteCommandParams &, Callback<llvm::json::Value>);
   void onWorkspaceSymbol(const WorkspaceSymbolParams &,
                          Callback<std::vector<SymbolInformation>>);
   void onRename(const RenameParams &, Callback<WorkspaceEdit>);
   void onHover(const TextDocumentPositionParams &,

clangd/ClangdLSPServer.cpp

Server->locateSymbolAt(
             }
             Reply(std::move(Decls));
           },
           std::move(Reply)));
 }
 
 void ClangdLSPServer::onSwitchSourceHeader(
     const TextDocumentIdentifier &Params,
-    Callback<llvm::Optional<std::string>> Reply) {
+    Callback<llvm::Optional<URIForFile>> Reply) {
   if (auto Result = Server->switchSourceHeader(Params.uri.file()))
-    Reply(URI::resolvePath(*Result, Params.uri.file()));
+    Reply(URIForFile::canonicalize(*Result, Params.uri.file()));
   else
     Reply(llvm::None);
 }
 
 void ClangdLSPServer::onDocumentHighlight(
     const TextDocumentPositionParams &Params,
     Callback<std::vector<DocumentHighlight>> Reply) {
   Server->findDocumentHighlights(Params.textDocument.uri.file(),