(autoconf.info)Option Checking

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14.5 Controlling Checking of `configure' Options

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'.

     By default, disable warnings related to any unrecognized
     `--with-PACKAGE' or `--enable-FEATURE' options.  This is implied

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

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