configuration.ccl

[NOTE: The configuration.ccl is still relatively new, and not all features listed below may be fully implemented or functional.]

A configuration.ccl file defines capabilities which a thorn either provides or requires, or may use if available. Unlike implementations, only one thorn providing a particular capability may be compiled into a configuration at one time. Thus this mechanism may be used to, for example: provide access to external libraries; provide access to functions which other thorns must call, but are too complex for function aliasing; or to split a thorn into several thorns, all of which require some common (not aliased) functions.

A configuration options file can contain any number of the following sections:

• PROVIDES <Capability>
  {
    SCRIPT <Configuration script>
    LANG <Language>
    [OPTIONS [<option>[,<option>]...]]
  }
  

  Informs the CST that this thorn provides a given capability, and that this capability has a given detection script which may be used to configure it (e.g. running an autoconf script or detecting an external library's location). The script should output configuration information on its standard output -- the syntax is described below in Section E2.5.1. The script may also indicate the failure to detect a capability by returning a non-zero exit code; this will stop the build after the CST stage.

  Scripts can be in any language. If an interpreter is needed to run the script, for example Perl, this should be indicated by the LANG option.

  The specified options are checked for in the original configuration and any options passed on the command line (including an `options' file) at compile time when the thorn is added, or if the CST is rerun. These options need be set only once, and will be remembered between builds.

• REQUIRES  <Capability>
  

  Informs the CST that this thorn requires a certain capability to be present. If no thorn providing the capability is in the ThornList, the build will stop after the CST stage.

  OPTIONAL <Capability>
  {
    DEFINE <macro>
  }
  

  Informs the CST that this thorn may use a certain capability if a thorn providing it is in the ThornList. If present, the preprocessor macro macro will be defined and given the value ``1''.