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<h5 class="subsubsection">6.3.8.2 The Front End <samp><span class="file">config-lang.in</span></samp> File</h5>

<p>Each language subdirectory contains a <samp><span class="file">config-lang.in</span></samp> file. 
This file is a shell script that may define some variables describing
the language:

     <dl>
<dt><code>language</code><dd>This definition must be present, and gives the name of the language
for some purposes such as arguments to <samp><span class="option">--enable-languages</span></samp>. 
<br><dt><code>lang_requires</code><dd>If defined, this variable lists (space-separated) language front ends
other than C that this front end requires to be enabled (with the
names given being their <code>language</code> settings).  For example, the
Java front end depends on the C++ front end, so sets
&lsquo;<samp><span class="samp">lang_requires=c++</span></samp>&rsquo;. 
<br><dt><code>subdir_requires</code><dd>If defined, this variable lists (space-separated) front end directories
other than C that this front end requires to be present.  For example,
the Objective-C++ front end uses source files from the C++ and
Objective-C front ends, so sets &lsquo;<samp><span class="samp">subdir_requires="cp objc"</span></samp>&rsquo;. 
<br><dt><code>target_libs</code><dd>If defined, this variable lists (space-separated) targets in the top
level <samp><span class="file">Makefile</span></samp> to build the runtime libraries for this
language, such as <code>target-libobjc</code>. 
<br><dt><code>lang_dirs</code><dd>If defined, this variable lists (space-separated) top level
directories (parallel to <samp><span class="file">gcc</span></samp>), apart from the runtime libraries,
that should not be configured if this front end is not built. 
<br><dt><code>build_by_default</code><dd>If defined to &lsquo;<samp><span class="samp">no</span></samp>&rsquo;, this language front end is not built unless
enabled in a <samp><span class="option">--enable-languages</span></samp> argument.  Otherwise, front
ends are built by default, subject to any special logic in
<samp><span class="file">configure.ac</span></samp> (as is present to disable the Ada front end if the
Ada compiler is not already installed). 
<br><dt><code>boot_language</code><dd>If defined to &lsquo;<samp><span class="samp">yes</span></samp>&rsquo;, this front end is built in stage1 of the
bootstrap.  This is only relevant to front ends written in their own
languages. 
<br><dt><code>compilers</code><dd>If defined, a space-separated list of compiler executables that will
be run by the driver.  The names here will each end
with &lsquo;<samp><span class="samp">\$(exeext)</span></samp>&rsquo;. 
<br><dt><code>outputs</code><dd>If defined, a space-separated list of files that should be generated
by <samp><span class="file">configure</span></samp> substituting values in them.  This mechanism can
be used to create a file <samp><var>language</var><span class="file">/Makefile</span></samp> from
<samp><var>language</var><span class="file">/Makefile.in</span></samp>, but this is deprecated, building
everything from the single <samp><span class="file">gcc/Makefile</span></samp> is preferred. 
<br><dt><code>gtfiles</code><dd>If defined, a space-separated list of files that should be scanned by
<samp><span class="file">gengtype.c</span></samp> to generate the garbage collection tables and routines for
this language.  This excludes the files that are common to all front
ends.  See <a href="Type-Information.html#Type-Information">Type Information</a>.

 </dl>

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