Automatically generate c_cpp_properties.json from Makefile with a 99-line Ruby script

Makefile

CC:=gcc
CFLAGS:=\
-I./include\
-DFOO\
-DBAR\
-std=c11

.vscode/c_cpp_properties.json: Makefile
	ruby vscode_cprops_gen.rb .vscode $(CC) $(CFLAGS)

vscode_cprops_gen.rb

# Automatically generate VSCode intellisense settings from your makefile.
#
# Usage: ruby vscode_cprops_gen.rb (output_dir) (compiler) (cflags...)
#
# Makefile sample:
#   .vscode/c_cpp_properties.json: Makefile
#     @ruby vscode_cprops_gen.rb .vscode $(CC) $(CFLAGS)

require 'pathname'
require 'json'

CONFIG_NAME = "Project" # name of the output c/c++ configuration
GENERATE_FLYLINT = true # whether to copy the config into flylint's config

def which(cmd)
  # Thanks stackoverflow: https://stackoverflow.com/questions/2108727/which-in-ruby-checking-if-program-exists-in-path-from-ruby
  exts = ENV['PATHEXT'] ? ENV['PATHEXT'].split(';') : ['']
  ENV['PATH'].split(File::PATH_SEPARATOR).each do |path|
    exts.each do |ext|
      exe = File.join(path, "#{cmd}#{ext}")
      return exe if File.executable?(exe) && !File.directory?(exe)
    end
  end
  nil
end


outdir = Pathname.new(ARGV[0]).cleanpath
compiler_path = Pathname.new(which(ARGV[1])).cleanpath
wd = Pathname.new(Dir.getwd)
workspace_dir = wd.join(outdir).join("..").cleanpath

c_cpp_properties_json = outdir.join "c_cpp_properties.json"
settings_json = outdir.join "settings.json"

include_paths = []
defines = []
c_std = nil
cpp_std = nil

ARGV[2..].each do |arg|
  if arg =~ /^-I/
    ipath = Pathname.new(arg[2..]).cleanpath
    relpath = wd.join(ipath).relative_path_from(workspace_dir)
    include_paths.push "${workspaceFolder}/#{relpath}"
  elsif arg =~ /^-D/
    defines.push arg[2..]
  elsif arg =~ /^-std=/
    if arg.include? "++"
      cpp_std = arg[5..]
    else
      c_std = arg[5..]
    end
  end
end

unless File.exists? c_cpp_properties_json
  default_json = {
    version: 4,
    configurations: []
  }
  File.write c_cpp_properties_json, JSON.pretty_generate(default_json)
end

properties = {
  'name' => CONFIG_NAME,
  'includePath' => include_paths,
  'defines' => defines,
  'compilerPath' => compiler_path,
}
properties['cStandard'] = c_std if c_std
properties['cppStandard'] = cpp_std if cpp_std

json = JSON.parse File.read(c_cpp_properties_json)
did_update = json['configurations'].any? do |cfg|
  if cfg['name'] == CONFIG_NAME
    cfg.merge! properties
  end
end

unless did_update
  json['configurations'].push properties
end

File.write c_cpp_properties_json, JSON.pretty_generate(json)

if GENERATE_FLYLINT
  unless File.exists? settings_json
    File.write settings_json, JSON.pretty_generate({})
  end

  json = JSON.parse File.read(settings_json)
  json["c-cpp-flylint.includePaths"] = include_paths
  json["c-cpp-flylint.defines"] = defines
  json["c-cpp-flylint.standard"] = [c_std, cpp_std].filter { |s| !s.nil? }

  File.write settings_json, JSON.pretty_generate(json)
end