[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 +1,90 @@
+//===-------------- 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.
+  PathRef getSourceForModuleName(StringRef ModuleName) const;
+
+  /// Return the direct required modules. Indirect required modules are not
+  /// included.
+  std::vector<std::string> getRequiredModules(PathRef File);
+
+private:
+  const GlobalCompilationDatabase &CDB;
+  const ThreadsafeFS &TFS;
+
+  // Whether the scanner has scanned the project globally.
+  bool GlobalScanned = false;
+
+  clang::tooling::dependencies::DependencyScanningService Service;
+
+  // TODO: Add a scanning cache.
+
+  // Map module name to source file path.
----------------
sam-mccall wrote:

somewhere (either here or on the public interface), please describe how this works for modules that are defined by multiple source files

(AIUI these "module names" may also include the partition, and the "source file" is only the module interface, not implementation units. This is fine and I think it's ok to say "module name" and "source file", just we should spell it out somewhere)

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