cargo_builder.rb

# frozen_string_literal: true

# This class is used by rubygems to build Rust extensions. It is a thin-wrapper
# over the `cargo rustc` command which takes care of building Rust code in a way
# that Ruby can use.
class Gem::Ext::CargoBuilder < Gem::Ext::Builder
  attr_accessor :spec, :runner, :profile

  def initialize(spec)
    require_relative "../command"
    require_relative "cargo_builder/link_flag_converter"

    @spec = spec
    @runner = self.class.method(:run)
    @profile = :release
  end

  def build(_extension, dest_path, results, args = [], lib_dir = nil, cargo_dir = Dir.pwd)
    require "fileutils"
    require "shellwords"

    build_crate(dest_path, results, args, cargo_dir)
    validate_cargo_build!(dest_path)
    rename_cdylib_for_ruby_compatibility(dest_path)
    finalize_directory(dest_path, lib_dir, cargo_dir)
    results
  end

  def build_crate(dest_path, results, args, cargo_dir)
    env = build_env
    cmd = cargo_command(cargo_dir, dest_path, args)
    runner.call cmd, results, "cargo", cargo_dir, env

    results
  end

  def build_env
    build_env = rb_config_env
    build_env["RUBY_STATIC"] = "true" if ruby_static? && ENV.key?("RUBY_STATIC")
    build_env["RUSTFLAGS"] = "#{ENV["RUSTFLAGS"]} --cfg=rb_sys_gem".strip
    build_env
  end

  def cargo_command(cargo_dir, dest_path, args = [])
    manifest = File.join(cargo_dir, "Cargo.toml")
    cargo = ENV.fetch("CARGO", "cargo")

    cmd = []
    cmd += [cargo, "rustc"]
    cmd += ["--target", ENV["CARGO_BUILD_TARGET"]] if ENV["CARGO_BUILD_TARGET"]
    cmd += ["--target-dir", dest_path]
    cmd += ["--manifest-path", manifest]
    cmd += ["--lib"]
    cmd += ["--profile", profile.to_s]
    cmd += ["--locked"] if profile == :release
    cmd += Gem::Command.build_args
    cmd += args
    cmd += ["--"]
    cmd += [*cargo_rustc_args(dest_path)]
    cmd
  end

  private

  def rb_config_env
    result = {}
    RbConfig::CONFIG.each {|k, v| result["RBCONFIG_#{k}"] = v }
    result
  end

  def cargo_rustc_args(dest_dir)
    [
      *linker_args,
      *mkmf_libpath,
      *rustc_dynamic_linker_flags(dest_dir),
      *rustc_lib_flags(dest_dir),
      *platform_specific_rustc_args(dest_dir),
      *debug_flags,
    ]
  end

  def platform_specific_rustc_args(dest_dir, flags = [])
    if mingw_target?
      # On mingw platforms, mkmf adds libruby to the linker flags
      flags += libruby_args(dest_dir)

      # Make sure ALSR is used on mingw
      # see https://github.com/rust-lang/rust/pull/75406/files
      flags += ["-C", "link-arg=-Wl,--dynamicbase"]
      flags += ["-C", "link-arg=-Wl,--disable-auto-image-base"]

      # If the gem is installed on a host with build tools installed, but is
      # run on one that isn't the missing libraries will cause the extension
      # to fail on start.
      flags += ["-C", "link-arg=-static-libgcc"]
    elsif darwin_target?
      # Ventura does not always have this flag enabled
      flags += ["-C", "link-arg=-Wl,-undefined,dynamic_lookup"]
    end

    flags
  end

  # We want to use the same linker that Ruby uses, so that the linker flags from
  # mkmf work properly.
  def linker_args
    # Have to handle CC="cl /nologo" on mswin
    cc_flag = Shellwords.split(makefile_config("CC"))
    linker = cc_flag.shift
    link_args = cc_flag.flat_map {|a| ["-C", "link-arg=#{a}"] }

    ["-C", "linker=#{linker}", *link_args]
  end

  def libruby_args(dest_dir)
    libs = makefile_config(ruby_static? ? "LIBRUBYARG_STATIC" : "LIBRUBYARG_SHARED")
    raw_libs = Shellwords.split(libs)
    raw_libs.flat_map {|l| ldflag_to_link_modifier(l) }
  end

  def ruby_static?
    return true if %w[1 true].include?(ENV["RUBY_STATIC"])

    makefile_config("ENABLE_SHARED") == "no"
  end

  # Ruby expects the dylib to follow a file name convention for loading
  def rename_cdylib_for_ruby_compatibility(dest_path)
    new_path = final_extension_path(dest_path)
    FileUtils.cp(cargo_dylib_path(dest_path), new_path)
    new_path
  end

  def validate_cargo_build!(dir)
    dylib_path = cargo_dylib_path(dir)

    raise DylibNotFoundError, dir unless File.exist?(dylib_path)

    dylib_path
  end

  def final_extension_path(dest_path)
    dylib_path = cargo_dylib_path(dest_path)
    dlext_name = "#{spec.name}.#{makefile_config("DLEXT")}"
    dylib_path.gsub(File.basename(dylib_path), dlext_name)
  end

  def cargo_dylib_path(dest_path)
    prefix = so_ext == "dll" ? "" : "lib"
    path_parts = [dest_path]
    path_parts << ENV["CARGO_BUILD_TARGET"] if ENV["CARGO_BUILD_TARGET"]
    path_parts += [profile_target_directory, "#{prefix}#{cargo_crate_name}.#{so_ext}"]
    File.join(*path_parts)
  end

  def cargo_crate_name
    spec.metadata.fetch("cargo_crate_name", spec.name).tr("-", "_")
  end

  def rustc_dynamic_linker_flags(dest_dir)
    split_flags("DLDFLAGS")
      .map {|arg| maybe_resolve_ldflag_variable(arg, dest_dir) }
      .compact
      .flat_map {|arg| ldflag_to_link_modifier(arg) }
  end

  def rustc_lib_flags(dest_dir)
    split_flags("LIBS").flat_map {|arg| ldflag_to_link_modifier(arg) }
  end

  def split_flags(var)
    Shellwords.split(RbConfig::CONFIG.fetch(var, ""))
  end

  def ldflag_to_link_modifier(arg)
    LinkFlagConverter.convert(arg)
  end

  def msvc_target?
    makefile_config("target_os").include?("msvc")
  end

  def darwin_target?
    makefile_config("target_os").include?("darwin")
  end

  def mingw_target?
    makefile_config("target_os").include?("mingw")
  end

  def win_target?
    target_platform = RbConfig::CONFIG["target_os"]
    !!Gem::WIN_PATTERNS.find {|r| target_platform =~ r }
  end

  # Interpolate substition vars in the arg (i.e. $(DEFFILE))
  def maybe_resolve_ldflag_variable(input_arg, dest_dir)
    var_matches = input_arg.match(/\$\((\w+)\)/)

    return input_arg unless var_matches

    var_name = var_matches[1]

    return input_arg if var_name.nil? || var_name.chomp.empty?

    case var_name
    # On windows, it is assumed that mkmf has setup an exports file for the
    # extension, so we have to to create one ourselves.
    when "DEFFILE"
      write_deffile(dest_dir)
    else
      RbConfig::CONFIG[var_name]
    end
  end

  def write_deffile(dest_dir)
    deffile_path = File.join(dest_dir, "#{spec.name}-#{RbConfig::CONFIG["arch"]}.def")
    export_prefix = makefile_config("EXPORT_PREFIX") || ""

    File.open(deffile_path, "w") do |f|
      f.puts "EXPORTS"
      f.puts "#{export_prefix.strip}Init_#{spec.name}"
    end

    deffile_path
  end

  # We have to basically reimplement RbConfig::CONFIG['SOEXT'] here to support
  # Ruby < 2.5
  #
  # @see https://github.com/ruby/ruby/blob/c87c027f18c005460746a74c07cd80ee355b16e4/configure.ac#L3185
  def so_ext
    return RbConfig::CONFIG["SOEXT"] if RbConfig::CONFIG.key?("SOEXT")

    if win_target?
      "dll"
    elsif darwin_target?
      "dylib"
    else
      "so"
    end
  end

  # Corresponds to $(LIBPATH) in mkmf
  def mkmf_libpath
    ["-L", "native=#{makefile_config("libdir")}"]
  end

  def makefile_config(var_name)
    val = RbConfig::MAKEFILE_CONFIG[var_name]

    return unless val

    RbConfig.expand(val.dup)
  end

  # Good balance between binary size and debugability
  def debug_flags
    return [] if profile == :dev

    ["-C", "debuginfo=1"]
  end

  # Copied from ExtConfBuilder
  def finalize_directory(dest_path, lib_dir, extension_dir)
    require "fileutils"
    require "tempfile"

    ext_path = final_extension_path(dest_path)

    begin
      tmp_dest = Dir.mktmpdir(".gem.", extension_dir)

      # Some versions of `mktmpdir` return absolute paths, which will break make
      # if the paths contain spaces.
      #
      # As such, we convert to a relative path.
      tmp_dest_relative = get_relative_path(tmp_dest.clone, extension_dir)

      full_tmp_dest = File.join(extension_dir, tmp_dest_relative)

      # TODO: remove in RubyGems 4
      if Gem.install_extension_in_lib && lib_dir
        FileUtils.mkdir_p lib_dir
        FileUtils.cp_r ext_path, lib_dir, remove_destination: true
      end

      FileUtils::Entry_.new(full_tmp_dest).traverse do |ent|
        destent = ent.class.new(dest_path, ent.rel)
        destent.exist? || FileUtils.mv(ent.path, destent.path)
      end
    ensure
      FileUtils.rm_rf tmp_dest if tmp_dest
    end
  end

  def get_relative_path(path, base)
    path[0..base.length - 1] = "." if path.start_with?(base)
    path
  end

  def profile_target_directory
    case profile
    when :release then "release"
    when :dev     then "debug"
    else          raise "unknown target directory for profile: #{profile}"
    end
  end

  # Error raised when no cdylib artifact was created
  class DylibNotFoundError < StandardError
    def initialize(dir)
      files = Dir.glob(File.join(dir, "**", "*")).map {|f| "- #{f}" }.join "\n"

      super <<~MSG
        Dynamic library not found for Rust extension (in #{dir})

        Make sure you set "crate-type" in Cargo.toml to "cdylib"

        Found files:
        #{files}
      MSG
    end
  end
end