[clangd] Set minimum gRPC version to 1.27

[kbobyrev]

Summary

gRPC 1.26 and earlier are affected by bugs preventing remote index from working:

• https://github.com/grpc/grpc/issues/21280
• https://github.com/grpc/grpc/issues/21213

This patch sets minimum version of gRPC to 1.27 when it is installed manually
or via APT on Debian-like Linux distributions or via Homebrew on macOS.

Related Debian bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=965217

[kbobyrev]

Check gRPC version for system-installed APT package on Debian-like Linux
distros.

[kbobyrev]

Aww, this might be problematic. Ubuntu has quite old gRPC versions (which are OK though). The newest is 1.26.0 and it's on Groovy (20.10, unreleased yet).

[kbobyrev]

Maybe wait for Debian packages to get updated and then whitelist 1.26.0-4 but fail with anything lower than that.

[kbobyrev]

This patch is not ready for review yet; planned changes: check if the version is between 1.25.0 and 1.26.0-4 and bail out in such cases.

[kbobyrev]

Rebase on top of master.

[kbobyrev]

Add macOS version check.

[kbobyrev]

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=965217 is not going anywhere, I think we should just add this check and not check for the correct patch on Debian (and macOS is different anyway).

[kbobyrev]

Need to exclude everything between 1.26.0 and 1.27.0, not set this as the minimum (Ubuntu packages are outdated).

[kbobyrev]

There are more revisions that are buggy, can't test them all :(

clang-tools-extra/clangd/index/remote/README.md

 # Clangd remote index
 
 Clangd uses a global index for project-wide code completion, navigation and
 other features.  For large projects, building this can take many hours and
 keeping it loaded uses a lot of memory.
 
 To relieve that burden, we're building remote index — a global index
 served on a different machine and shared between developers. This directory
 contains code that is used as Proof of Concept for the upcoming remote index
 feature.
 
 ## Building
 
-This feature uses gRPC and Protobuf libraries, so you will need to install them.
-There are two ways of doing that.
+This feature uses gRPC (known to work with versions starting from 1.27.0) and
+Protobuf libraries, so you will need to install them. There are two ways of
+doing that.
 
 However you install dependencies, to enable this feature and build remote index
 tools you will need to set this CMake flag — `-DCLANGD_ENABLE_REMOTE=On`.
 
 ### System-installed libraries
 
 On Debian-like systems gRPC and Protobuf can be installed from apt:
 

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)
   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})
+  find_package(gRPC 1.27 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()
   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 $PATH for Clangd remote index build")
   endif()
   # On macOS the libraries are typically installed via Homebrew and are not on
   # the system path.
   if (${APPLE})
+    # FIXME(kirillbobyrev): Check gRPC version for macOS, too.
     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)
       execute_process(COMMAND ${HOMEBREW} --prefix grpc
         OUTPUT_VARIABLE GRPC_HOMEBREW_PATH
         RESULT_VARIABLE GRPC_HOMEBREW_RETURN_CODE
         OUTPUT_STRIP_TRAILING_WHITESPACE)
       execute_process(COMMAND ${HOMEBREW} --prefix protobuf
         OUTPUT_VARIABLE PROTOBUF_HOMEBREW_PATH
         RESULT_VARIABLE PROTOBUF_HOMEBREW_RETURN_CODE
         OUTPUT_STRIP_TRAILING_WHITESPACE)
       # If either library is not installed via Homebrew, fall back to the
       # system path.
       if (GRPC_HOMEBREW_RETURN_CODE EQUAL "0")
         include_directories(${GRPC_HOMEBREW_PATH}/include)
         link_directories(${GRPC_HOMEBREW_PATH}/lib)
       endif()
       if (PROTOBUF_HOMEBREW_RETURN_CODE EQUAL "0")
         include_directories(${PROTOBUF_HOMEBREW_PATH}/include)
         link_directories(${PROTOBUF_HOMEBREW_PATH}/lib)
       endif()
     endif()
+  elseif(CMAKE_HOST_SYSTEM_NAME STREQUAL "Linux")
+    # Try to figure out gRPC version using APT for Debian-like Linux
+    # distributions.
+    find_program(APT apt)
+    if (NOT APT-NOTFOUND)
+      execute_process(COMMAND ${APT} policy libgrpc++-dev
+        OUTPUT_VARIABLE APT_GRPC_POLICY
+        RESULT_VARIABLE APT_GRPC_POLICY_RETURN_CODE)
+      if (APT_GRPC_POLICY_RETURN_CODE EQUAL "0")
+        # Parse MAJOR.MINOR gRPC version.
+        string(REGEX MATCH "Installed: ([0-9]+\\.[0-9]+)"
+          gRPC_VERSION ${APT_GRPC_POLICY})
+        if (CMAKE_MATCH_1 VERSION_LESS "1.27")
+          message(FATAL_ERROR "gRPC version rerquied: >=1.27, found: ${CMAKE_MATCH_1}")
+        endif()
+        message(STATUS "Using gRPC ${gRPC_VERSION}")
+      endif()
+    endif()
   endif()
 endif()
 
 # Proto headers are generated in ${CMAKE_CURRENT_BINARY_DIR}.
 # Libraries that use these headers should adjust the include path.
 # FIXME(kirillbobyrev): Allow optional generation of gRPC code and give callers
 # control over it via additional parameters.
 function(generate_grpc_protos LibraryName ProtoFile)