Revert "[clangd] Add feature modules registry" (#154711)

Reverts #153756

It leads to new build bot failure.
https://lab.llvm.org/buildbot/#/builders/145/builds/9200

```
BUILD FAILED: failed build (failure)

Step 5 (build-unified-tree) failure: build (failure) ...
254.983 [140/55/1504] Building CXX object tools/clang/tools/extra/clangd/tool/CMakeFiles/obj.clangdMain.dir/ClangdMain.cpp.o
FAILED: tools/clang/tools/extra/clangd/tool/CMakeFiles/obj.clangdMain.dir/ClangdMain.cpp.o
ccache /home/buildbots/llvm-external-buildbots/clang.19.1.7/bin/clang++ --gcc-toolchain=/gcc-toolchain/usr -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/tools/clang/tools/extra/clangd/tool -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/tool -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/../include-cleaner/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/tools/clang/tools/extra/clangd/../clang-tidy -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-
 rhel-test/clang-ppc64le-rhel/build/tools/clang/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/tools/clang/tools/extra/clangd -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe  -unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -Wno-nested-anon-types -O3 -DNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -MD -MT tools/clang/tools/extra/clangd/tool/CMakeFiles/obj.clangdMain.dir/ClangdMain.cpp.o -MF tools/clang/tools/extra/clangd/tool/CMakeFiles/obj.clangdMain.dir/ClangdMain.cpp.o.d -o tools/clang/tools/extra/clangd/tool/CMakeFiles/obj.clangdMain.dir/ClangdMain.cpp.o -c /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/tool/ClangdMain.cpp
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/tool/ClangdMain.cpp:10:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/ClangdLSPServer.h:12:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/ClangdServer.h:12:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/CodeComplete.h:18:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/ASTSignals.h:12:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/ParsedAST.h:23:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/CollectMacros.h:12:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/Protocol.h:26:
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/URI.h:14:
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/include/llvm/Support/Registry.h:110:47: error: instantiation of variable 'llvm::Registry<clang::clangd::FeatureModule>::Head' required here, but no definition is available [-Werror,-Wundefined-var-template]
  110 |     static iterator begin() { return iterator(Head); }
      |                                               ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/include/llvm/Support/Registry.h:114:25: note: in instantiation of member function 'llvm::Registry<clang::clangd::FeatureModule>::begin' requested here
  114 |       return make_range(begin(), end());
      |                         ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/clang-tools-extra/clangd/tool/ClangdMain.cpp:1021:64: note: in instantiation of member function 'llvm::Registry<clang::clangd::FeatureModule>::entries' requested here
 1021 |   for (FeatureModuleRegistry::entry E : FeatureModuleRegistry::entries()) {
      |                                                                ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/include/llvm/Support/Registry.h:61:18: note: forward declaration of template entity is here
   61 |     static node *Head;
      |                  ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/include/llvm/Support/Registry.h:110:47: note: add an explicit instantiation declaration to suppress this warning if 'llvm::Registry<clang::clangd::FeatureModule>::Head' is explicitly instantiated in another translation unit
  110 |     static iterator begin() { return iterator(Head); }
      |                                               ^
1 error generated.
```

I need some time to fix this in a correct way

Author: ArcsinX

clang-tools-extra/clangd/FeatureModule.cpp

@@ -22,10 +22,6 @@ FeatureModule::Facilities &FeatureModule::facilities() {
   return *Fac;
 }
 
-void FeatureModuleSet::add(std::unique_ptr<FeatureModule> M) {
-  Modules.push_back(std::move(M));
-}
-
 bool FeatureModuleSet::addImpl(void *Key, std::unique_ptr<FeatureModule> M,
                                const char *Source) {
   if (!Map.try_emplace(Key, M.get()).second) {
@@ -39,5 +35,3 @@ bool FeatureModuleSet::addImpl(void *Key, std::unique_ptr<FeatureModule> M,
 
 } // namespace clangd
 } // namespace clang
-
-LLVM_INSTANTIATE_REGISTRY(clang::clangd::FeatureModuleRegistry)

clang-tools-extra/clangd/FeatureModule.h

@@ -15,7 +15,6 @@
 #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>
@@ -144,14 +143,9 @@ class FeatureModule {
 
 /// A FeatureModuleSet is a collection of feature modules installed in clangd.
 ///
-/// 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.
+/// 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.
 ///
 /// The set owns the modules. It is itself owned by main, not ClangdServer.
 class FeatureModuleSet {
@@ -178,7 +172,6 @@ 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);
   template <typename Mod> bool add(std::unique_ptr<Mod> M) {
     return addImpl(&ID<Mod>::Key, std::move(M), LLVM_PRETTY_FUNCTION);
   }
@@ -192,8 +185,6 @@ class FeatureModuleSet {
 
 template <typename Mod> int FeatureModuleSet::ID<Mod>::Key;
 
-using FeatureModuleRegistry = llvm::Registry<FeatureModule>;
-
 } // namespace clangd
 } // namespace clang
 #endif

clang-tools-extra/clangd/tool/ClangdMain.cpp

@@ -1017,14 +1017,6 @@ 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());
-  }
-  if (ModuleSet.begin() != ModuleSet.end())
-    Opts.FeatureModules = &ModuleSet;
-
   // Initialize and run ClangdLSPServer.
   // Change stdin to binary to not lose \r\n on windows.
   llvm::sys::ChangeStdinToBinary();