##### 6.3.8.1 The Front End `language` Directory

A front end `language` directory contains the source files of that front end (but not of any runtime libraries, which should be outside the `gcc` directory). This includes documentation, and possibly some subsidiary programs built alongside the front end. Certain files are special and other parts of the compiler depend on their names:

`config-lang.in`
  This file is required in all language subdirectories. See The Front End `config-lang.in` File, for details of its contents
`Make-lang.in`
  This file is required in all language subdirectories. See The Front End `Make-lang.in` File, for details of its contents.
`lang.opt`
  This file registers the set of switches that the front end accepts on the command line, and their `--help` text. See Options.
`lang-specs.h`
  This file provides entries for `default_compilers` in `gcc.c` which override the default of giving an error that a compiler for that language is not installed.
`language-tree.def`
  This file, which need not exist, defines any language-specific tree codes.