[clangd] Warn developers when trying to link system-installed gRPC statically

[sammccall]

Just hijacking to ask for some extra comments :-)

llvm/cmake/modules/FindGRPC.cmake

0–1

can we move this comment inside the if?
currently it looks like it applies to the whole file.

And mention whether we're going to link static or dynamically, or if it depends on BUILD_SHARED_LIBS

25

similarly, can we add a comment here? mentioning the overall "system-installed GRPC" idea,
and then explicitly saying something like

"We always link dynamically in this mode. While the static libraries are usually installed, the CMake files telling us *which* static libraries to link are not".

26

nit: comma after "linking"

[kbobyrev]

Address post-LGTM comments.

llvm/cmake/modules/FindGRPC.cmake

-# This setup requires gRPC to be built from sources using CMake and installed to
-# ${GRPC_INSTALL_PATH} via -DCMAKE_INSTALL_PREFIX=${GRPC_INSTALL_PATH}.
 # FIXME(kirillbobyrev): Check if gRPC and Protobuf headers can be included at
 # configure time.
 if (GRPC_INSTALL_PATH)
+  # This setup requires gRPC to be built from sources using CMake and installed
+  # to ${GRPC_INSTALL_PATH} via -DCMAKE_INSTALL_PREFIX=${GRPC_INSTALL_PATH}.
+  # gRPC and Protobuf will be linked statically.
   set(protobuf_MODULE_COMPATIBLE TRUE)
   find_package(Protobuf CONFIG REQUIRED HINTS ${GRPC_INSTALL_PATH})
   message(STATUS "Using protobuf ${protobuf_VERSION}")
   find_package(gRPC CONFIG REQUIRED HINTS ${GRPC_INSTALL_PATH})
   message(STATUS "Using gRPC ${gRPC_VERSION}")
 
   include_directories(${Protobuf_INCLUDE_DIRS})
 
   # gRPC CMake CONFIG gives the libraries slightly odd names, make them match
   # the conventional system-installed names.
   set_target_properties(protobuf::libprotobuf PROPERTIES IMPORTED_GLOBAL TRUE)
   add_library(protobuf ALIAS protobuf::libprotobuf)
   set_target_properties(gRPC::grpc++ PROPERTIES IMPORTED_GLOBAL TRUE)
   add_library(grpc++ ALIAS gRPC::grpc++)
 
   set(GRPC_CPP_PLUGIN $<TARGET_FILE:gRPC::grpc_cpp_plugin>)
   set(PROTOC ${Protobuf_PROTOC_EXECUTABLE})
 else()
+  # This setup requires system-installed gRPC and Protobuf.
+  # We always link dynamically in this mode. While the static libraries are
+  # usually installed, the CMake files telling us *which* static libraries to
+  # link are not.
+  if (NOT BUILD_SHARED_LIBS)
+    message(NOTICE "gRPC and Protobuf will be linked dynamically. If you want static linking, build gRPC from sources.")
+  endif()
   find_program(GRPC_CPP_PLUGIN grpc_cpp_plugin)
   find_program(PROTOC protoc)
   if (GRPC_CPP_PLUGIN-NOTFOUND OR PROTOC-NOTFOUND)
-    message(FATAL_ERROR "gRPC C++ Plugin and Protoc must be on $PATH for Clangd remote index build")
+    message(FATAL_ERROR "gRPC C++ Plugin and Protoc must be on $PATH for Clangd remote index build.")
   endif()
   # On macOS the libraries are typically installed via Homebrew and are not on
   # the system path.
   if (${APPLE})
     find_program(HOMEBREW brew)
     # If Homebrew is not found, the user might have installed libraries
     # manually. Fall back to the system path.
     if (NOT HOMEBREW-NOTFOUND)