Make clangd-fuzzer use the normal add_llvm_fuzzer() machinery

[thakis]

Summary

This allows building it even if no fuzzer is enabled. (Sadly, it only builds on Linux at the moment.)

[bkramer]

lg

clang-tools-extra/clangd/CMakeLists.txt

add_clang_library(clangDaemon
   clangToolingCore
   clangToolingInclusions
   clangToolingRefactor
   ${LLVM_PTHREAD_LIB}
   ${CLANGD_ATOMIC_LIB}
   )
 
 add_subdirectory(refactor/tweaks)
-if( LLVM_LIB_FUZZING_ENGINE OR LLVM_USE_SANITIZE_COVERAGE )
+if (LINUX)
+  # FIXME: Make fuzzer not use linux-specific APIs, build it everywhere.
   add_subdirectory(fuzzer)
 endif()
 add_subdirectory(tool)
 add_subdirectory(indexer)
 add_subdirectory(index/dex/dexp)
 
 if (LLVM_INCLUDE_BENCHMARKS)
   add_subdirectory(benchmarks)
 endif()
 if ( CLANGD_BUILD_XPC )
   add_subdirectory(xpc)
 endif ()

clang-tools-extra/clangd/fuzzer/CMakeLists.txt

 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/..)
 
 set(LLVM_LINK_COMPONENTS support)
 
-if(LLVM_USE_SANITIZE_COVERAGE)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=fuzzer")
-endif()
-
-add_clang_executable(clangd-fuzzer
-  EXCLUDE_FROM_ALL
-  ClangdFuzzer.cpp
+# This fuzzer runs on oss-fuzz, so keep it around even if it looks unreferenced.
+add_llvm_fuzzer(clangd-fuzzer
+  clangd-fuzzer.cpp
+  DUMMY_MAIN DummyClangdMain.cpp
   )
 
 target_link_libraries(clangd-fuzzer
   PRIVATE
   clangBasic
   clangDaemon
   clangFormat
   clangFrontend
   clangSema
   clangTooling
   clangToolingCore
-  ${LLVM_LIB_FUZZING_ENGINE}
   )

clang-tools-extra/clangd/fuzzer/DummyClangdMain.cpp

+//===---- DummyClangdMain.cpp - Entry point to sanity check the fuzzer ----===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Implementation of main so we can build and test without linking libFuzzer.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/FuzzMutate/FuzzerCLI.h"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
+int main(int argc, char *argv[]) {
+  return llvm::runFuzzerOnInputs(argc, argv, LLVMFuzzerTestOneInput);
+}