[GHC] #12598: configure script: --enable-unregisterised default printed incorrectly

[GHC]

#12598: configure script: --enable-unregisterised default printed incorrectly
-------------------------------------+-------------------------------------
           Reporter:  mistydemeo     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Build System   |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The help text for the --enable-unregisterised flag to configure renders
 incorrectly. Instead of printing the actual default, it instead prints the
 name of the variable holding the default:

 {{{
   --enable-unregisterised Build an unregisterised compiler (enabled by
 default
                           on platforms without registerised support)
                           [default="$UnregisterisedDefault"]
 }}}

 This happens because the help text is generated via a call to the
 `AC_HELP_STRING` macro:

 {{{#!m4
 AC_HELP_STRING([--enable-unregisterised],
 [Build an unregisterised compiler (enabled by default on platforms without
 registerised support) [default="$UnregisterisedDefault"]])
 }}}

 According to the autoconf documentation, "the second argument of
 `AS_HELP_STRING` is treated as a whitespace separated list of text to be
 reformatted, and is not subject to macro expansion." (https://www.gnu.org
 /savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Pretty-
 Help-Strings.html) - hence why the name of the variable is included in the
 output instead of its value.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12598>
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