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

[kadir çetinkaya via cfe-commits]

================
@@ -0,0 +1,199 @@
+//===------------------ ProjectModules.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
+//
+//===----------------------------------------------------------------------===//
+
+#include "ProjectModules.h"
+
+#include "support/Logger.h"
+
+#include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
+#include "clang/Tooling/DependencyScanning/DependencyScanningTool.h"
+
+namespace clang::clangd {
+namespace {
+/// 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(vector<PathRef>)` member
+/// function. See the comments of `globalScan` to see the details.
+///
+/// The ModuleDependencyScanner can get the directly required module names for a
+/// specific source file. Also the ModuleDependencyScanner can get the source
+/// file declaring the primary module interface for 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
+/// interfere with each other.
+class ModuleDependencyScanner {
+public:
+  ModuleDependencyScanner(
+      std::shared_ptr<const clang::tooling::CompilationDatabase> 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.
+  std::optional<ModuleDependencyInfo> scan(PathRef FilePath);
+
+  /// Scanning every source file in the current project to get the
+  /// <module-name> to <module-unit-source> map.
+  /// 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 the end users)
+  /// to provide the map.
+  void globalScan();
+
+  /// 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.
+  ///
+  /// TODO: We should handle the case that there are multiple source files
+  /// declaring the same module.
+  PathRef getSourceForModuleName(llvm::StringRef ModuleName) const;
+
+  /// Return the direct required modules. Indirect required modules are not
+  /// included.
+  std::vector<std::string> getRequiredModules(PathRef File);
+
+private:
+  std::shared_ptr<const clang::tooling::CompilationDatabase> 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.
+  llvm::StringMap<std::string> ModuleNameToSource;
+};
+
+std::optional<ModuleDependencyScanner::ModuleDependencyInfo>
+ModuleDependencyScanner::scan(PathRef FilePath) {
+  auto Candidates = CDB->getCompileCommands(FilePath);
+  if (Candidates.empty())
+    return std::nullopt;
+
+  // Choose the first candidates as the compile commands as the file.
+  // Following the same logic with
+  // DirectoryBasedGlobalCompilationDatabase::getCompileCommand.
+  tooling::CompileCommand Cmd = std::move(Candidates.front());
----------------
kadircet wrote:

can you also inject `-resource-dir` via `CompilerInvocation::GetResourcesPath` ? i think it's worth calling it once during constructor of `ModuleDependencyScanner` and storing as a member.

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