1 files changed, 32 insertions, 0 deletions
diff --git a/tool/mkconfig.rb b/tool/mkconfig.rb
index c3d3230d34..ec39e5f8bd 100755
--- a/tool/mkconfig.rb
+++ b/tool/mkconfig.rb
@@ -310,6 +310,38 @@ print <<EOS
     RbConfig::expand(val)
   end
 
+  # :nodoc:
+  # call-seq:
+  #
+  #   RbConfig.fire_update!(key, val)               -> string
+  #   RbConfig.fire_update!(key, val, mkconf, conf) -> string
+  #
+  # updates +key+ in +mkconf+ with +val+, and all values depending on
+  # the +key+ in +mkconf+.
+  #
+  #   RbConfig::MAKEFILE_CONFIG.values_at("CC", "LDSHARED") # => ["gcc", "$(CC) -shared"]
+  #   RbConfig::CONFIG.values_at("CC", "LDSHARED")          # => ["gcc", "gcc -shared"]
+  #   RbConfig.fire_update!("CC", "gcc-8")                  # => ["CC", "LDSHARED"]
+  #   RbConfig::MAKEFILE_CONFIG.values_at("CC", "LDSHARED") # => ["gcc-8", "$(CC) -shared"]
+  #   RbConfig::CONFIG.values_at("CC", "LDSHARED")          # => ["gcc-8", "gcc-8 -shared"]
+  #
+  # returns updated keys list, or +nil+ if nothing changed.
+  def RbConfig.fire_update!(key, val, mkconf = MAKEFILE_CONFIG, conf = CONFIG)
+    return if (old = mkconf[key]) == val
+    mkconf[key] = val
+    keys = [key]
+    deps = []
+    begin
+      re = Regexp.new("\\\\$\\\\((?:%1$s)\\\\)|\\\\$\\\\{(?:%1$s)\\\\}" % keys.join('|'))
+      deps |= keys
+      keys.clear
+      mkconf.each {|k,v| keys << k if re =~ v}
+    end until keys.empty?
+    deps.each {|k| conf[k] = mkconf[k].dup}
+    deps.each {|k| expand(conf[k])}
+    deps
+  end
+
   # call-seq:
   #
   #   RbConfig.ruby -> path