Generate compile_commands.json by default

[driazati]

This is low overhead (it only affects the make-generation step, not the actual build) and makes developer tooling like clangd work much better, so we should have it on by default instead of off (which is CMake's default). If necessary, it can be disabled with

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=0 ...

or adding this to config.cmake

set(CMAKE_EXPORT_COMPILE_COMMANDS OFF)

If CMake is run from a subproject, this does nothing and leaves it to the parent to configure. For example, this does not generate compile_commands.json by default:

cmake_minimum_required(VERSION 2.0 FATAL_ERROR)
project(test)
add_subdirectory(tvm)
add_executable(test test.cpp)

cc @areusch

[junrushao]

Yeah usually we need compile_commands.json by default, so I'm in favor of doing so. Not a cmake expert, just curious, is it better to put this in CMakeList.txt or config.cmake? What if TVM is used as a CMake submodule by other projects?

[driazati]

I think it's better in CMakeLists.txt since everyone will get it automatically rather than having to update any cmake configs they use, but the point about avoiding messing with parent projects is good. It looks like that can be detected so it can avoid setting anything in that case, I will follow up with a fix soon

[junrushao]

Thank you @driazati for the explanation!!

[areusch]

thanks, this makes sense. one question for you