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

[Chuanqi Xu via cfe-commits]

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@@ -0,0 +1,106 @@
+//===-------------- 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.
+///
+/// ModuleDependencyScanner should only be used via ScanningAllProjectModules.
+///
+/// The ModuleDependencyScanner can get the directly required module name for a
+/// specific source file. Also the ModuleDependencyScanner can get the source
+/// file declaring a specific module name.
+///
+/// IMPORTANT NOTE: we assume that every module unit is only declared once in a
+/// source file in the project. But the assumption is not strictly true even
+/// besides the invalid projects. The language specification requires that every
+/// module unit should be unique in a valid program. But a project can contain
+/// multiple programs. Then it is valid that we can have multiple source files
+/// declaring the same module in a project as long as these source files don't
+/// interere with each other.`
+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.
----------------
ChuanqiXu9 wrote:

I just thought it will be better if it has less interfaces. Then currently `scan()` is not directly called outside the class so I add the note. But I see your thoughts about ModuleDependencyScanner to treat it as a self-contained class. I feel it good too. So I'd like to remove the note.

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