HackStudio: Add C++ Language Server

The language server keeps track of the content of currently edited
files by receiving updates about edit actions.

Also, C++ autocompletion is no longer tied to HackStudio itself and
moved to be part of the language server.

13 files changed, 421 insertions, 13 deletions

diff --git a/DevTools/HackStudio/CMakeLists.txt b/DevTools/HackStudio/CMakeLists.txt
index c279dcddfb..b8f35978b7 100644
--- a/DevTools/HackStudio/CMakeLists.txt
+++ b/DevTools/HackStudio/CMakeLists.txt
@@ -1,7 +1,9 @@
+add_subdirectory(LanguageServers)
+add_subdirectory(LanguageClients)
+
 set(SOURCES
     AutoCompleteBox.cpp
     CodeDocument.cpp
-    CppAutoComplete.cpp
     CursorTool.cpp
     Debugger/BacktraceModel.cpp
     Debugger/DebugInfoWidget.cpp
@@ -33,3 +35,4 @@ set(SOURCES
 
 serenity_bin(HackStudio)
 target_link_libraries(HackStudio LibWeb LibMarkdown LibGUI LibGfx LibCore LibVT LibDebug LibX86 LibDiff LibShell)
+add_dependencies(HackStudio CppLanguageServer)
diff --git a/DevTools/HackStudio/LanguageClients/CMakeLists.txt b/DevTools/HackStudio/LanguageClients/CMakeLists.txt
new file mode 100644
index 0000000000..cdeb442a1d
--- /dev/null
+++ b/DevTools/HackStudio/LanguageClients/CMakeLists.txt
@@ -0,0 +1 @@
+add_subdirectory(Cpp)
diff --git a/DevTools/HackStudio/LanguageClients/Cpp/CMakeLists.txt b/DevTools/HackStudio/LanguageClients/Cpp/CMakeLists.txt
new file mode 100644
index 0000000000..f669bba3ed
--- /dev/null
+++ b/DevTools/HackStudio/LanguageClients/Cpp/CMakeLists.txt
@@ -0,0 +1,4 @@
+ set(GENERATED_SOURCES 
+    ../../LanguageServers/Cpp/CppLanguageServerEndpoint.h
+    ../../LanguageServers/Cpp/CppLanguageClientEndpoint.h
+ ) 
diff --git a/DevTools/HackStudio/LanguageClients/Cpp/ServerConnection.h b/DevTools/HackStudio/LanguageClients/Cpp/ServerConnection.h
new file mode 100644
index 0000000000..9b916f42e4
--- /dev/null
+++ b/DevTools/HackStudio/LanguageClients/Cpp/ServerConnection.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/LanguageServers/Cpp/CppLanguageClientEndpoint.h>
+#include <DevTools/HackStudio/LanguageServers/Cpp/CppLanguageServerEndpoint.h>
+#include <LibIPC/ServerConnection.h>
+
+namespace LanguageClients {
+namespace Cpp {
+
+class ServerConnection : public IPC::ServerConnection<CppLanguageClientEndpoint, CppLanguageServerEndpoint>
+    , public CppLanguageClientEndpoint {
+    C_OBJECT(ServerConnection)
+public:
+    virtual void handshake() override
+    {
+        auto response = send_sync<Messages::CppLanguageServer::Greet>(m_project_path.string());
+        set_my_client_id(response->client_id());
+    }
+
+private:
+    ServerConnection(const String& project_path)
+        : IPC::ServerConnection<CppLanguageClientEndpoint, CppLanguageServerEndpoint>(*this, "/tmp/portal/language/cpp")
+        , m_project_path(project_path)
+    {
+    }
+
+    virtual void handle(const Messages::CppLanguageClient::Dummy&) override { }
+
+    LexicalPath m_project_path;
+};
+
+}
+}
diff --git a/DevTools/HackStudio/LanguageServers/CMakeLists.txt b/DevTools/HackStudio/LanguageServers/CMakeLists.txt
new file mode 100644
index 0000000000..cdeb442a1d
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/CMakeLists.txt
@@ -0,0 +1 @@
+add_subdirectory(Cpp)
diff --git a/DevTools/HackStudio/CppAutoComplete.cpp b/DevTools/HackStudio/LanguageServers/Cpp/AutoComplete.cpp
index dfd56cccdf..1ebdd9a8d6 100644
--- a/DevTools/HackStudio/CppAutoComplete.cpp
+++ b/DevTools/HackStudio/LanguageServers/Cpp/AutoComplete.cpp
@@ -24,17 +24,18 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "CppAutoComplete.h"
+#include "AutoComplete.h"
 #include <AK/HashTable.h>
 #include <LibCpp/Lexer.h>
 
 // #define DEBUG_AUTOCOMPLETE
 
-namespace HackStudio {
-Vector<String> CppAutoComplete::get_suggestions(const String& code, GUI::TextPosition autocomplete_position)
+namespace LanguageServers::Cpp {
+
+Vector<String> AutoComplete::get_suggestions(const String& code, GUI::TextPosition autocomplete_position)
 {
     auto lines = code.split('\n', true);
-    Cpp::Lexer lexer(code);
+    Lexer lexer(code);
     auto tokens = lexer.lex();
 
     auto index_of_target_token = token_in_position(tokens, autocomplete_position);
@@ -52,12 +53,12 @@ Vector<String> CppAutoComplete::get_suggestions(const String& code, GUI::TextPos
     return suggestions;
 }
 
-String CppAutoComplete::text_of_token(const Vector<String> lines, const Cpp::Token& token)
+String AutoComplete::text_of_token(const Vector<String> lines, const Cpp::Token& token)
 {
     return lines[token.m_start.line].substring(token.m_start.column, token.m_end.column - token.m_start.column + 1);
 }
 
-Optional<size_t> CppAutoComplete::token_in_position(const Vector<Cpp::Token>& tokens, GUI::TextPosition position)
+Optional<size_t> AutoComplete::token_in_position(const Vector<Cpp::Token>& tokens, GUI::TextPosition position)
 {
     for (size_t token_index = 0; token_index < tokens.size(); ++token_index) {
         auto& token = tokens[token_index];
@@ -70,7 +71,7 @@ Optional<size_t> CppAutoComplete::token_in_position(const Vector<Cpp::Token>& to
     return {};
 }
 
-Vector<String> CppAutoComplete::identifier_prefixes(const Vector<String> lines, const Vector<Cpp::Token>& tokens, size_t target_token_index)
+Vector<String> AutoComplete::identifier_prefixes(const Vector<String> lines, const Vector<Cpp::Token>& tokens, size_t target_token_index)
 {
     auto partial_input = text_of_token(lines, tokens[target_token_index]);
     Vector<String> suggestions;
@@ -89,4 +90,5 @@ Vector<String> CppAutoComplete::identifier_prefixes(const Vector<String> lines,
     }
     return suggestions;
 }
-};
+
+}
diff --git a/DevTools/HackStudio/CppAutoComplete.h b/DevTools/HackStudio/LanguageServers/Cpp/AutoComplete.h
index 6ab5a4c03a..ad0104f5e1 100644
--- a/DevTools/HackStudio/CppAutoComplete.h
+++ b/DevTools/HackStudio/LanguageServers/Cpp/AutoComplete.h
@@ -31,10 +31,13 @@
 #include <LibCpp/Lexer.h>
 #include <LibGUI/TextPosition.h>
 
-namespace HackStudio {
-class CppAutoComplete {
+namespace LanguageServers::Cpp {
+
+using namespace ::Cpp;
+
+class AutoComplete {
 public:
-    CppAutoComplete() = delete;
+    AutoComplete() = delete;
 
     static Vector<String> get_suggestions(const String& code, GUI::TextPosition autocomplete_position);
 
@@ -43,4 +46,5 @@ private:
     static String text_of_token(const Vector<String> lines, const Cpp::Token&);
     static Vector<String> identifier_prefixes(const Vector<String> lines, const Vector<Cpp::Token>&, size_t target_token_index);
 };
-};
+
+}
diff --git a/DevTools/HackStudio/LanguageServers/Cpp/CMakeLists.txt b/DevTools/HackStudio/LanguageServers/Cpp/CMakeLists.txt
new file mode 100644
index 0000000000..65d146295b
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/Cpp/CMakeLists.txt
@@ -0,0 +1,16 @@
+compile_ipc(CppLanguageServer.ipc CppLanguageServerEndpoint.h)
+compile_ipc(CppLanguageClient.ipc CppLanguageClientEndpoint.h)
+
+set(SOURCES
+    ClientConnection.cpp
+    main.cpp
+    CppLanguageServerEndpoint.h
+    CppLanguageClientEndpoint.h
+    AutoComplete.cpp
+)
+
+serenity_bin(CppLanguageServer)
+
+# We link with LibGUI because we use GUI::TextDocument to update 
+# the content of files according to the edit actions we receive over IPC.
+target_link_libraries(CppLanguageServer LibIPC LibCpp LibGUI)
diff --git a/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.cpp b/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.cpp
new file mode 100644
index 0000000000..21b820a814
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.cpp
@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ClientConnection.h"
+#include "AutoComplete.h"
+#include <AK/HashMap.h>
+#include <LibCore/File.h>
+#include <LibGUI/TextDocument.h>
+
+// #define DEBUG_CPP_LANGUAGE_SERVER
+// #define DEBUG_FILE_CONTENT
+
+namespace LanguageServers::Cpp {
+
+static HashMap<int, RefPtr<ClientConnection>> s_connections;
+
+ClientConnection::ClientConnection(NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+    : IPC::ClientConnection<CppLanguageClientEndpoint, CppLanguageServerEndpoint>(*this, move(socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+}
+
+void ClientConnection::die()
+{
+    s_connections.remove(client_id());
+    exit(0);
+}
+
+OwnPtr<Messages::CppLanguageServer::GreetResponse> ClientConnection::handle(const Messages::CppLanguageServer::Greet& message)
+{
+    m_project_root = LexicalPath(message.project_root());
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbg() << "project_root: " << m_project_root.string();
+#endif
+    return make<Messages::CppLanguageServer::GreetResponse>(client_id());
+}
+
+class DefaultDocumentClient final : public GUI::TextDocument::Client {
+public:
+    virtual ~DefaultDocumentClient() override = default;
+    virtual void document_did_append_line() override {};
+    virtual void document_did_insert_line(size_t) override {};
+    virtual void document_did_remove_line(size_t) override {};
+    virtual void document_did_remove_all_lines() override {};
+    virtual void document_did_change() override {};
+    virtual void document_did_set_text() override {};
+    virtual void document_did_set_cursor(const GUI::TextPosition&) override {};
+
+    virtual bool is_automatic_indentation_enabled() const override { return true; }
+    virtual int soft_tab_width() const { return 4; }
+};
+
+static DefaultDocumentClient s_default_document_client;
+
+void ClientConnection::handle(const Messages::CppLanguageServer::FileOpened& message)
+{
+    LexicalPath file_path(String::format("%s/%s", m_project_root.string().characters(), message.file_name().characters()));
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbg() << "FileOpened: " << file_path.string();
+#endif
+
+    auto file = Core::File::construct(file_path.string());
+    if (!file->open(Core::IODevice::ReadOnly)) {
+        errno = file->error();
+        perror("open");
+        dbg() << "Failed to open project file: " << file_path.string();
+        return;
+    }
+    auto content = file->read_all();
+    StringView content_view(content);
+    auto document = GUI::TextDocument::create(&s_default_document_client);
+    document->set_text(content_view);
+    m_open_files.set(message.file_name(), document);
+#ifdef DEBUG_FILE_CONTENT
+    dbg() << document->text();
+#endif
+}
+
+void ClientConnection::handle(const Messages::CppLanguageServer::FileEditInsertText& message)
+{
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbg() << "InsertText for file: " << message.file_name();
+    dbg() << "Text: " << message.text();
+    dbg() << "[" << message.start_line() << ":" << message.start_column() << "]";
+#endif
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbg() << "file " << message.file_name() << " has not been opened";
+        return;
+    }
+    GUI::TextPosition start_position { (size_t)message.start_line(), (size_t)message.start_column() };
+    document->insert_at(start_position, message.text(), &s_default_document_client);
+#ifdef DEBUG_FILE_CONTENT
+    dbg() << document->text();
+#endif
+}
+
+void ClientConnection::handle(const Messages::CppLanguageServer::FileEditRemoveText& message)
+{
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbg() << "RemoveText for file: " << message.file_name();
+    dbg() << "[" << message.start_line() << ":" << message.start_column() << " - " << message.end_line() << ":" << message.end_column() << "]";
+#endif
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbg() << "file " << message.file_name() << " has not been opened";
+        return;
+    }
+    GUI::TextPosition start_position { (size_t)message.start_line(), (size_t)message.start_column() };
+    GUI::TextRange range {
+        GUI::TextPosition { (size_t)message.start_line(),
+            (size_t)message.start_column() },
+        GUI::TextPosition { (size_t)message.end_line(),
+            (size_t)message.end_column() }
+    };
+
+    document->remove(range);
+#ifdef DEBUG_FILE_CONTENT
+    dbg() << document->text();
+#endif
+}
+
+// FIXME: The work we do here could be taxing and block the client for a significant time.
+//        Would should turn this to an async IPC endpoint and report the reuslts back in a separate Server->Client message.
+OwnPtr<Messages::CppLanguageServer::AutoCompleteSuggestionsResponse> ClientConnection::handle(const Messages::CppLanguageServer::AutoCompleteSuggestions& message)
+{
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbg() << "AutoCompleteSuggestions for: " << message.file_name() << " " << message.cursor_line() << ":" << message.cursor_column();
+#endif
+
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbg() << "file " << message.file_name() << " has not been opened";
+        return nullptr;
+    }
+
+    Vector<String> suggestions = AutoComplete::get_suggestions(document->text(), { (size_t)message.cursor_line(), (size_t)message.cursor_column() });
+    return make<Messages::CppLanguageServer::AutoCompleteSuggestionsResponse>(suggestions);
+}
+
+RefPtr<GUI::TextDocument> ClientConnection::document_for(const String& file_name)
+{
+    auto document_optional = m_open_files.get(file_name);
+    if (!document_optional.has_value())
+        return nullptr;
+
+    return document_optional.value();
+}
+
+void ClientConnection::handle(const Messages::CppLanguageServer::SetFileContent& message)
+{
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbg() << "file " << message.file_name() << " has not been opened";
+        return;
+    }
+    auto content = message.content();
+    document->set_text(content.view());
+}
+
+}
diff --git a/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.h b/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.h
new file mode 100644
index 0000000000..428cfe7893
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.h
@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/LanguageServers/Cpp/CppLanguageClientEndpoint.h>
+#include <DevTools/HackStudio/LanguageServers/Cpp/CppLanguageServerEndpoint.h>
+#include <LibGUI/TextDocument.h>
+#include <LibIPC/ClientConnection.h>
+
+namespace LanguageServers::Cpp {
+
+class ClientConnection final
+    : public IPC::ClientConnection<CppLanguageClientEndpoint, CppLanguageServerEndpoint>
+    , public CppLanguageServerEndpoint {
+    C_OBJECT(ClientConnection);
+
+public:
+    explicit ClientConnection(NonnullRefPtr<Core::LocalSocket>, int client_id);
+    ~ClientConnection() override;
+
+    virtual void die() override;
+
+private:
+    virtual OwnPtr<Messages::CppLanguageServer::GreetResponse> handle(const Messages::CppLanguageServer::Greet&) override;
+    virtual void handle(const Messages::CppLanguageServer::FileOpened&) override;
+    virtual void handle(const Messages::CppLanguageServer::FileEditInsertText&) override;
+    virtual void handle(const Messages::CppLanguageServer::FileEditRemoveText&) override;
+    virtual void handle(const Messages::CppLanguageServer::SetFileContent&) override;
+    virtual OwnPtr<Messages::CppLanguageServer::AutoCompleteSuggestionsResponse> handle(const Messages::CppLanguageServer::AutoCompleteSuggestions&) override;
+
+    RefPtr<GUI::TextDocument> document_for(const String& file_name);
+
+    LexicalPath m_project_root;
+    HashMap<String, NonnullRefPtr<GUI::TextDocument>> m_open_files;
+};
+
+}
diff --git a/DevTools/HackStudio/LanguageServers/Cpp/CppLanguageClient.ipc b/DevTools/HackStudio/LanguageServers/Cpp/CppLanguageClient.ipc
new file mode 100644
index 0000000000..47ae7f6fb6
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/Cpp/CppLanguageClient.ipc
@@ -0,0 +1,4 @@
+endpoint CppLanguageClient = 8002
+{
+    Dummy() =|
+}
diff --git a/DevTools/HackStudio/LanguageServers/Cpp/CppLanguageServer.ipc b/DevTools/HackStudio/LanguageServers/Cpp/CppLanguageServer.ipc
new file mode 100644
index 0000000000..7265cc6f2e
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/Cpp/CppLanguageServer.ipc
@@ -0,0 +1,11 @@
+endpoint CppLanguageServer = 8001
+{
+    Greet(String project_root) => (i32 client_id)
+
+    FileOpened(String file_name) =|
+    FileEditInsertText(String file_name, String text, i32 start_line, i32 start_column) =|
+    FileEditRemoveText(String file_name, i32 start_line, i32 start_column, i32 end_line, i32 end_column) =|
+    SetFileContent(String file_name, String content) =|
+
+    AutoCompleteSuggestions(String file_name, i32 cursor_line, i32 cursor_column) => (Vector<String> suggestions)
+}
diff --git a/DevTools/HackStudio/LanguageServers/Cpp/main.cpp b/DevTools/HackStudio/LanguageServers/Cpp/main.cpp
new file mode 100644
index 0000000000..9d9ac3ee98
--- /dev/null
+++ b/DevTools/HackStudio/LanguageServers/Cpp/main.cpp
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibCore/LocalServer.h>
+#include <LibIPC/ClientConnection.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int main(int, char**)
+{
+    Core::EventLoop event_loop;
+    if (pledge("stdio unix rpath", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    auto socket = Core::LocalSocket::take_over_accepted_socket_from_system_server();
+    IPC::new_client_connection<LanguageServers::Cpp::ClientConnection>(socket.release_nonnull(), 1);
+    if (pledge("stdio rpath", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+    return event_loop.exec();
+}