[clang-tools-extra] [clangd] [C++20] [Modules] Introduce initial support for C++20 Modules (PR #66462)

[Chuanqi Xu via cfe-commits]

================
@@ -0,0 +1,71 @@
+//===----------------- ModulesBuilder.h --------------------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Experimental support for C++20 Modules.
+//
+// Currently we simplify the implementations by preventing reusing module files
+// across different versions and different source files. But this is clearly a
+// waste of time and space in the end of the day.
+//
+// FIXME: Supporting reusing module files across different versions and
+// different source files.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULES_BUILDER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULES_BUILDER_H
+
+#include "GlobalCompilationDatabase.h"
+#include "ProjectModules.h"
+
+#include "support/Path.h"
+#include "support/ThreadsafeFS.h"
+
+#include "llvm/ADT/SmallString.h"
+
+#include <memory>
+
+namespace clang {
+namespace clangd {
+
+class PrerequisiteModules;
+
+/// This class handles building module files for a given source file.
+///
+/// In the future, we want the class to manage the module files acorss
+/// different versions and different source files.
+class ModulesBuilder {
+public:
+  ModulesBuilder() = delete;
+
+  ModulesBuilder(const GlobalCompilationDatabase &CDB) : CDB(CDB) {}
+
+  ModulesBuilder(const ModulesBuilder &) = delete;
+  ModulesBuilder(ModulesBuilder &&) = delete;
+
+  ModulesBuilder &operator=(const ModulesBuilder &) = delete;
+  ModulesBuilder &operator=(ModulesBuilder &&) = delete;
----------------
ChuanqiXu9 wrote:

Primarily a conservative design. Since this is owned by the ClangdLSPServer, and it looks like we won't copy or move the server. Then it is safe to mark it as non-copyable and non-movable. It may be easy to convert a non-moveable and non-copyable to the opposite. But it is not the case vice versa. 

https://github.com/llvm/llvm-project/pull/66462