File: autoconf.info,  Node: Option Checking,  Next: Site Details,  Prev: Pretty Help Strings,  Up: Site Configuration

15.5 Controlling Checking of ‘configure’ Options
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The ‘configure’ script checks its command-line options against a list of
known options, like ‘--help’ or ‘--config-cache’.  An unknown option
ordinarily indicates a mistake by the user and ‘configure’ halts with an
error.  However, by default unknown ‘--with-PACKAGE’ and
‘--enable-FEATURE’ options elicit only a warning, to support configuring
entire source trees.

   Source trees often contain multiple packages with a top-level
‘configure’ script that uses the ‘AC_CONFIG_SUBDIRS’ macro (*note
Subdirectories::).  Because the packages generally support different
‘--with-PACKAGE’ and ‘--enable-FEATURE’ options, the GNU Coding
Standards say they must accept unrecognized options without halting.
Even a warning message is undesirable here, so ‘AC_CONFIG_SUBDIRS’
automatically disables the warnings.

   This default behavior may be modified in two ways.  First, the
installer can invoke ‘configure --disable-option-checking’ to disable
these warnings, or invoke ‘configure --enable-option-checking=fatal’
options to turn them into fatal errors, respectively.  Second, the
maintainer can use ‘AC_DISABLE_OPTION_CHECKING’.

 -- Macro: AC_DISABLE_OPTION_CHECKING

     By default, disable warnings related to any unrecognized
     ‘--with-PACKAGE’ or ‘--enable-FEATURE’ options.  This is implied by
     ‘AC_CONFIG_SUBDIRS’.

     The installer can override this behavior by passing
     ‘--enable-option-checking’ (enable warnings) or
     ‘--enable-option-checking=fatal’ (enable errors) to ‘configure’.