chore: Set up code completion request handling in LSP server

packages/cxx-gen-lsp/src/gen_requests_h.ts

@@ -19,7 +19,7 @@
 // SOFTWARE.
 
 import * as path from "node:path";
-import { MetaModel, toCppType, Request, Notification, isRequest } from "./MetaModel.js";
+import { MetaModel, toCppType, Request, Notification, isRequest, Property, Structure } from "./MetaModel.js";
 import { writeFileSync } from "node:fs";
 import { copyrightHeader } from "./copyrightHeader.js";
 
@@ -96,9 +96,27 @@ export function gen_requests_h({ model, outputDirectory }: { model: MetaModel; o
       emit();
       emit(`  auto id(std::variant<long, std::string> id) -> ${responseTypeName}&;`);
       emit();
-      emit(`  [[nodiscard]] auto result() const -> ${resultType};`);
-      emit();
-      emit(`  auto result(${resultType} result) -> ${responseTypeName}&;`);
+
+      const structure: Structure = {
+        name: responseTypeName,
+        properties: [{ name: "result", type: request.result, optional: false }],
+      };
+
+      structure.properties.forEach((property) => {
+        const propertyName = property.name;
+        const returnType = toCppType(property.type);
+        emit();
+        emit(`    [[nodiscard ]]auto ${propertyName}() const -> ${returnType};`);
+        if (property.type.kind === "or") {
+          emit();
+          emit(`template <typename T>`);
+          emit(`[[nodiscard]] auto ${propertyName}() -> T {`);
+          emit(`  auto& value = (*repr_)["${propertyName}"];`);
+          emit(`  return T(value);`);
+          emit(`}`);
+        }
+      });
+
       emit(`};`);
     }
   });

src/lsp/cxx/lsp/cxx_document.cc

@@ -202,6 +202,12 @@ void CxxDocument::cancel() {
 
 auto CxxDocument::fileName() const -> const std::string& { return d->fileName; }
 
+void CxxDocument::requestCodeCompletion(std::uint32_t line,
+                                        std::uint32_t column) {
+  auto& unit = d->unit;
+  unit.preprocessor()->requestCodeCompletionAt(line, column);
+}
+
 void CxxDocument::parse(std::string source) {
   d->configure();
 

src/lsp/cxx/lsp/cxx_document.h

@@ -39,6 +39,8 @@ class CxxDocument {
 
   [[nodiscard]] auto fileName() const -> const std::string&;
 
+  void requestCodeCompletion(std::uint32_t line, std::uint32_t column);
+
   void parse(std::string source);
 
   [[nodiscard]] auto version() const -> long;

src/lsp/cxx/lsp/lsp_server.cc

@@ -364,6 +364,11 @@ void Server::operator()(InitializeRequest request) {
     capabilities.textDocumentSync(TextDocumentSyncKind::kIncremental);
     capabilities.documentSymbolProvider(true);
 
+    auto completionOptions =
+        capabilities.completionProvider<CompletionOptions>();
+
+    completionOptions.triggerCharacters({":", ".", ">"});
+
     sendToClient(response);
   });
 }
@@ -478,6 +483,37 @@ void Server::operator()(DocumentSymbolRequest request) {
   });
 }
 
+void Server::operator()(CompletionRequest request) {
+  logTrace(std::format("Did receive CompletionRequest"));
+
+  auto textDocument = request.params().textDocument();
+  auto uri = textDocument.uri();
+  auto id = request.id();
+  auto line = request.params().position().line();
+  auto column = request.params().position().character();
+
+  const auto& text = documentContents_.at(uri);
+  auto value = text.value;
+
+  run([=, this, fileName = pathFromUri(uri)] {
+    withUnsafeJson([&](json storage) {
+      // the version is not relevant for code completion requests as we don't
+      // need to store the document in the cache.
+      auto cxxDocument = std::make_shared<CxxDocument>(cli, std::move(fileName),
+                                                       /*version=*/0);
+
+      // cxx expects 1-based line and column numbers
+      cxxDocument->requestCodeCompletion(line + 1, column + 1);
+      cxxDocument->parse(std::move(value));
+
+      CompletionResponse response(storage);
+      response.id(request.id());
+      auto completionItems = response.result<Vector<CompletionItem>>();
+      sendToClient(response);
+    });
+  });
+}
+
 void Server::operator()(CancelNotification notification) {
   const auto id = notification.params().id();
 

src/lsp/cxx/lsp/lsp_server.h

@@ -58,6 +58,7 @@ class Server {
   void operator()(DidChangeTextDocumentNotification notification);
 
   void operator()(DocumentSymbolRequest request);
+  void operator()(CompletionRequest request);
 
   void operator()(SetTraceNotification notification);