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

[Sam McCall via cfe-commits]

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@@ -0,0 +1,278 @@
+//===----------------- PrerequisiteModules.cpp -----------------------*-
+//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
+//
+//===----------------------------------------------------------------------===//
+
+#include "PrerequisiteModules.h"
+#include "ProjectModules.h"
+#include "support/Logger.h"
+
+#include "clang/Frontend/FrontendAction.h"
+#include "clang/Frontend/FrontendActions.h"
+#include "clang/Serialization/ASTReader.h"
+
+namespace clang {
+namespace clangd {
+
+namespace {
+llvm::SmallString<128> getAbsolutePath(const tooling::CompileCommand &Cmd) {
+  llvm::SmallString<128> AbsolutePath;
+  if (llvm::sys::path::is_absolute(Cmd.Filename)) {
+    AbsolutePath = Cmd.Filename;
+  } else {
+    AbsolutePath = Cmd.Directory;
+    llvm::sys::path::append(AbsolutePath, Cmd.Filename);
+    llvm::sys::path::remove_dots(AbsolutePath, true);
+  }
+  return AbsolutePath;
+}
+} // namespace
+
+PrerequisiteModules::PrerequisiteModules(PathRef MainFile,
+                                         const GlobalCompilationDatabase &CDB) {
+  std::optional<ProjectInfo> PI = CDB.getProjectInfo(MainFile);
+  if (!PI)
+    return;
+
+  llvm::SmallString<128> Result(PI->SourceRoot);
+  llvm::sys::path::append(Result, ".cache");
+  llvm::sys::path::append(Result, "clangd");
+  llvm::sys::path::append(Result, "module_files");
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sam-mccall wrote:

nit: just `modules` I think

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