MakeMakefile#depend_rules

# File tmp/rubies/ruby-4.1.0-preview1/lib/mkmf.rb, line 2269
def depend_rules(depend)
  suffixes = []
  depout = []
  cont = implicit = nil
  impconv = proc do
    each_compile_rules {|rule| depout << (rule % implicit[0]) << implicit[1]}
    implicit = nil
  end
  ruleconv = proc do |line|
    if implicit
      if /\A\t/ =~ line
        implicit[1] << line
        next
      else
        impconv[]
      end
    end
    if m = /\A\.(\w+)\.(\w+)(?:\s*:)/.match(line)
      suffixes << m[1] << m[2]
      implicit = [[m[1], m[2]], [m.post_match]]
      next
    elsif RULE_SUBST and /\A(?!\s*\w+\s*=)[$\w][^#]*:/ =~ line
      line.sub!(/\s*\#.*$/, '')
      comment = $&
      line.gsub!(%r"(\s)(?!\.)([^$(){}+=:\s\\,]+)(?=\s|\z)") {$1 + RULE_SUBST % $2}
      line = line.chomp + comment + "\n" if comment
    end
    depout << line
  end
  depend.each_line do |line|
    line.gsub!(/\.o\b/, ".#{$OBJEXT}")
    line.gsub!(/\{\$\(VPATH\)\}/, "") unless $nmake
    line.gsub!(/\$\((?:hdr|top)dir\)\/config.h/, $config_h)
    if $nmake && /\A\s*\$\(RM|COPY\)/ =~ line
      line.gsub!(%r"[-\w\./]{2,}"){$&.tr("/", "\\")}
      line.gsub!(/(\$\((?!RM|COPY)[^:)]+)(?=\))/, '\1:/=\\')
    end
    if /(?:^|[^\\])(?:\\\\)*\\$/ =~ line
      (cont ||= []) << line
      next
    elsif cont
      line = (cont << line).join
      cont = nil
    end
    ruleconv.call(line)
  end
  if cont
    ruleconv.call(cont.join)
  elsif implicit
    impconv.call
  end
  unless suffixes.empty?
    depout.unshift(".SUFFIXES: ." + suffixes.uniq.join(" .") + "\n\n")
  end
  if $extconf_h
    depout.unshift("$(OBJS): $(RUBY_EXTCONF_H)\n\n")
    depout.unshift("$(OBJS): $(hdrdir)/ruby/win32.h\n\n") if $mswin or $mingw
  end
  depout.flatten!
  depout
end