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

[Chuanqi Xu via cfe-commits]

================
@@ -0,0 +1,90 @@
+//===-------------- ModuleDependencyScanner.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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULEDEPENDENCYSCANNER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULEDEPENDENCYSCANNER_H
+
+#include "GlobalCompilationDatabase.h"
+#include "support/Path.h"
+#include "support/ThreadsafeFS.h"
+
+#include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
+#include "clang/Tooling/DependencyScanning/DependencyScanningTool.h"
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringMap.h"
+
+namespace clang {
+namespace clangd {
+
+/// A scanner to query the dependency information for C++20 Modules.
+///
+/// The scanner can scan a single file with `scan(PathRef)` member function
+/// or scan the whole project with `globalScan(PathRef)` member function. See
+/// the comments of `globalScan` to see the details.
+class ModuleDependencyScanner {
+public:
+  ModuleDependencyScanner(const GlobalCompilationDatabase &CDB,
+                          const ThreadsafeFS &TFS)
+      : CDB(CDB), TFS(TFS),
+        Service(tooling::dependencies::ScanningMode::CanonicalPreprocessing,
+                tooling::dependencies::ScanningOutputFormat::P1689) {}
+
+  // The scanned modules dependency information for a specific source file.
+  struct ModuleDependencyInfo {
+    // The name of the module if the file is a module unit.
+    std::optional<std::string> ModuleName;
+    // A list of names for the modules that the file directly depends.
+    std::vector<std::string> RequiredModules;
+  };
+
+  /// Scanning the single file specified by \param FilePath.
+  /// NOTE: This is only used by unittests for external uses.
+  std::optional<ModuleDependencyInfo> scan(PathRef FilePath);
+
+  /// Scanning every source file in the current project to get the
+  /// <module-name> to <module-unit-source> map.
+  /// It looks unefficiency to scan the whole project especially for
+  /// every version of every file!
+  /// TODO: We should find an efficient method to get the <module-name>
+  /// to <module-unit-source> map. We can make it either by providing
+  /// a global module dependency scanner to monitor every file. Or we
+  /// can simply require the build systems (or even if the end users)
+  /// to provide the map.
+  void globalScan(const std::vector<std::string> &AllFiles);
+  bool isGlobalScanned() const { return GlobalScanned; }
+
+  /// Get the source file from the module name. Note that the language
+  /// guarantees all the module names are unique in a valid program.
+  /// This function should only be called after globalScan.
+  /// FIXME: Maybe we should handle the corner cases.
----------------
ChuanqiXu9 wrote:

Done by expanding the FIXME.

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