[clangd] Introduce Modules

Modules can be used to augment clangd's behaviours in various features.

Differential Revision: https://reviews.llvm.org/D96244

clang-tools-extra/clangd/ClangdServer.cpp

@@ -127,7 +127,7 @@ ClangdServer::Options::operator TUScheduler::Options() const {
 ClangdServer::ClangdServer(const GlobalCompilationDatabase &CDB,
                            const ThreadsafeFS &TFS, const Options &Opts,
                            Callbacks *Callbacks)
-    : CDB(CDB), TFS(TFS),
+    : CDB(CDB), TFS(TFS), Modules(Opts.Modules),
       DynamicIdx(Opts.BuildDynamicSymbolIndex ? new FileIndex() : nullptr),
       ClangTidyProvider(Opts.ClangTidyProvider),
       WorkspaceRoot(Opts.WorkspaceRoot),

clang-tools-extra/clangd/ClangdServer.h

@@ -14,6 +14,7 @@
 #include "ConfigProvider.h"
 #include "GlobalCompilationDatabase.h"
 #include "Hover.h"
+#include "Module.h"
 #include "Protocol.h"
 #include "SemanticHighlighting.h"
 #include "TUScheduler.h"
@@ -142,6 +143,8 @@ public:
     /// Enable preview of FoldingRanges feature.
     bool FoldingRanges = false;
 
+    ModuleSet *Modules = nullptr;
+
     explicit operator TUScheduler::Options() const;
   };
   // Sensible default options for use in tests.
@@ -336,6 +339,7 @@ private:
 
   const GlobalCompilationDatabase &CDB;
   const ThreadsafeFS &TFS;
+  ModuleSet *Modules = nullptr;
 
   Path ResourceDir;
   // The index used to look up symbols. This could be:

clang-tools-extra/clangd/Headers.cpp

@@ -36,7 +36,7 @@ public:
                           CharSourceRange /*FilenameRange*/,
                           const FileEntry *File, llvm::StringRef /*SearchPath*/,
                           llvm::StringRef /*RelativePath*/,
-                          const Module * /*Imported*/,
+                          const clang::Module * /*Imported*/,
                           SrcMgr::CharacteristicKind FileKind) override {
     auto MainFID = SM.getMainFileID();
     // If an include is part of the preamble patch, translate #line directives.

clang-tools-extra/clangd/Module.h

@@ -0,0 +1,52 @@
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULE_H
+
+#include "llvm/ADT/StringRef.h"
+#include <memory>
+#include <vector>
+
+namespace clang {
+namespace clangd {
+
+/// A Module contributes a vertical feature to clangd.
+///
+/// FIXME: Extend this with LSP bindings to support reading/updating
+/// capabilities and implementing LSP endpoints.
+///
+/// The lifetime of a module is roughly:
+///  - modules are created before the LSP server, in ClangdMain.cpp
+///  - these modules are then passed to ClangdLSPServer and ClangdServer
+///    FIXME: LSP bindings should be registered at ClangdLSPServer
+///    initialization.
+///  - module hooks can be called at this point.
+///    FIXME: We should make some server facilities like TUScheduler and index
+///    available to those modules after ClangdServer is initalized.
+///  - ClangdServer will not be destroyed until all the requests are done.
+///    FIXME: Block server shutdown until all the modules are idle.
+///  - modules will be destroyed after ClangdLSPServer is destroyed.
+///
+/// Conventionally, standard modules live in the `clangd` namespace, and other
+/// exposed details live in a sub-namespace.
+class Module {
+public:
+  virtual ~Module() = default;
+};
+
+class ModuleSet {
+  std::vector<std::unique_ptr<Module>> Modules;
+
+public:
+  explicit ModuleSet(std::vector<std::unique_ptr<Module>> Modules)
+      : Modules(std::move(Modules)) {}
+
+  using iterator = llvm::pointee_iterator<decltype(Modules)::iterator>;
+  using const_iterator =
+      llvm::pointee_iterator<decltype(Modules)::const_iterator>;
+  iterator begin() { return iterator(Modules.begin()); }
+  iterator end() { return iterator(Modules.end()); }
+  const_iterator begin() const { return const_iterator(Modules.begin()); }
+  const_iterator end() const { return const_iterator(Modules.end()); }
+};
+} // namespace clangd
+} // namespace clang
+#endif

clang-tools-extra/clangd/unittests/ParsedASTTests.cpp

@@ -373,7 +373,7 @@ TEST(ParsedASTTest, ReplayPreambleForTidyCheckers) {
     void InclusionDirective(SourceLocation HashLoc, const Token &IncludeTok,
                             StringRef FileName, bool IsAngled,
                             CharSourceRange FilenameRange, const FileEntry *,
-                            StringRef, StringRef, const Module *,
+                            StringRef, StringRef, const clang::Module *,
                             SrcMgr::CharacteristicKind) override {
       Includes.emplace_back(SM, HashLoc, IncludeTok, FileName, IsAngled,
                             FilenameRange);