[clangd] Add feature modules registry

[ArcsinX]

This patch adds feature modules registry, as discussed with @kadircet in discourse.
Feature modules, which added into the feature module set from registry entries, can't expose public API, but still can be used via FeatureModule interface.

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clangd

Author: Aleksandr Platonov (ArcsinX)

Changes

This patch adds feature modules registry, as discussed with @kadircet in discourse.
Feature modules. which added into the feature module set from registry entries, can't expose public API, but still can be used via FeatureModule interface.

---

Full diff: https://github.com/llvm/llvm-project/pull/153756.diff

3 Files Affected:

• (modified) clang-tools-extra/clangd/FeatureModule.cpp (+2)
• (modified) clang-tools-extra/clangd/FeatureModule.h (+14-3)
• (modified) clang-tools-extra/clangd/tool/ClangdMain.cpp (+7)

diff --git a/clang-tools-extra/clangd/FeatureModule.cpp b/clang-tools-extra/clangd/FeatureModule.cpp
index 872cea1443789..47aff0b513f0d 100644
--- a/clang-tools-extra/clangd/FeatureModule.cpp
+++ b/clang-tools-extra/clangd/FeatureModule.cpp
@@ -9,6 +9,8 @@
 #include "FeatureModule.h"
 #include "support/Logger.h"
 
+LLVM_INSTANTIATE_REGISTRY(clang::clangd::FeatureModuleRegistry)
+
 namespace clang {
 namespace clangd {
 
diff --git a/clang-tools-extra/clangd/FeatureModule.h b/clang-tools-extra/clangd/FeatureModule.h
index 7b6883507be3f..3697a68ed4454 100644
--- a/clang-tools-extra/clangd/FeatureModule.h
+++ b/clang-tools-extra/clangd/FeatureModule.h
@@ -15,6 +15,7 @@
 #include "llvm/ADT/FunctionExtras.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/JSON.h"
+#include "llvm/Support/Registry.h"
 #include <memory>
 #include <optional>
 #include <type_traits>
@@ -143,9 +144,14 @@ class FeatureModule {
 
 /// A FeatureModuleSet is a collection of feature modules installed in clangd.
 ///
-/// Modules can be looked up by type, or used via the FeatureModule interface.
-/// This allows individual modules to expose a public API.
-/// For this reason, there can be only one feature module of each type.
+/// Modules added with explicit type specification can be looked up by type, or
+/// used via the FeatureModule interface. This allows individual modules to
+/// expose a public API. For this reason, there can be only one feature module
+/// of each type.
+///
+/// Modules added using a base class pointer can be used only via the
+/// FeatureModule interface and can't be looked up by type, thus custom public
+/// API (if provided by the module) can't be used.
 ///
 /// The set owns the modules. It is itself owned by main, not ClangdServer.
 class FeatureModuleSet {
@@ -172,6 +178,9 @@ class FeatureModuleSet {
   const_iterator begin() const { return const_iterator(Modules.begin()); }
   const_iterator end() const { return const_iterator(Modules.end()); }
 
+  void add(std::unique_ptr<FeatureModule> M) {
+    Modules.push_back(std::move(M));
+  }
   template <typename Mod> bool add(std::unique_ptr<Mod> M) {
     return addImpl(&ID<Mod>::Key, std::move(M), LLVM_PRETTY_FUNCTION);
   }
@@ -185,6 +194,8 @@ class FeatureModuleSet {
 
 template <typename Mod> int FeatureModuleSet::ID<Mod>::Key;
 
+typedef llvm::Registry<FeatureModule> FeatureModuleRegistry;
+
 } // namespace clangd
 } // namespace clang
 #endif
diff --git a/clang-tools-extra/clangd/tool/ClangdMain.cpp b/clang-tools-extra/clangd/tool/ClangdMain.cpp
index f287439f10cab..87c9f701d95ea 100644
--- a/clang-tools-extra/clangd/tool/ClangdMain.cpp
+++ b/clang-tools-extra/clangd/tool/ClangdMain.cpp
@@ -1017,6 +1017,13 @@ clangd accepts flags on the commandline, and in the CLANGD_FLAGS environment var
                : static_cast<int>(ErrorResultCode::CheckFailed);
   }
 
+  FeatureModuleSet ModuleSet;
+  for (FeatureModuleRegistry::entry E : FeatureModuleRegistry::entries()) {
+    vlog("Adding feature module '{0}' ({1})", E.getName(), E.getDesc());
+    ModuleSet.add(E.instantiate());
+  }
+  Opts.FeatureModules = &ModuleSet;
+
   // Initialize and run ClangdLSPServer.
   // Change stdin to binary to not lose \r\n on windows.
   llvm::sys::ChangeStdinToBinary();

[kadircet]

thanks!