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# ===========================================================================
# https://www.gnu.org/software/autoconf-archive/ax_am_override_var.html
# ===========================================================================
#
# SYNOPSIS
#
# AX_AM_OVERRIDE_VAR([varname1 varname ... ])
# AX_AM_OVERRIDE_FINALIZE
#
# DESCRIPTION
#
# This autoconf macro generalizes the approach given in
# <http://lists.gnu.org/archive/html/automake/2005-09/msg00108.html> which
# moves user specified values for variable 'varname' given at configure
# time into the corresponding AM_${varname} variable and clears out
# 'varname', allowing further manipulation by the configure script so that
# target specific variables can be given specialized versions. 'varname
# may still be specified on the make command line and will be appended as
# usual.
#
# As an example usage, consider a project which might benefit from
# different compiler flags for different components. Typically this is
# done via target specific flags, e.g.
#
# libgtest_la_CXXFLAGS = \
# -I $(top_srcdir)/tests \
# -I $(top_builddir)/tests \
# $(GTEST_CXXFLAGS)
#
# automake will automatically append $(CXXFLAGS) -- provided by the user
# -- to the build rule for libgtest_la. That might be problematic, as
# CXXFLAGS may contain compiler options which are inappropriate for
# libgtest_la.
#
# The approach laid out in the referenced mailing list message is to
# supply a base value for a variable during _configure_ time, during which
# it is possible to amend it for specific targets. The user may
# subsequently specify a value for the variable during _build_ time, which
# make will apply (via the standard automake rules) to all appropriate
# targets.
#
# For example,
#
# AX_AM_OVERRIDE_VAR([CXXFLAGS])
#
# will store the value of CXXFLAGS specified at configure time into the
# AM_CXXFLAGS variable, AC_SUBST it, and clear CXXFLAGS. configure may
# then create a target specific set of flags based upon AM_CXXFLAGS, e.g.
#
# # googletest uses variadic macros, which g++ -pedantic-errors
# # is very unhappy about
# AC_SUBST([GTEST_CXXFLAGS],
# [`AS_ECHO_N(["$AM_CXXFLAGS"]) \
# | sed s/-pedantic-errors/-pedantic/`
# ]
# )
#
# which would be used in a Makefile.am as above. Since CXXFLAGS is
# cleared, the configure time value will not affect the build for
# libgtest_la.
#
# Prior to _any other command_ which may set ${varname}, call
#
# AX_AM_OVERRIDE_VAR([varname])
#
# This will preserve the value (if any) passed to configure in
# AM_${varname} and AC_SUBST([AM_${varname}). You may pass a space
# separated list of variable names, or may call AX_AM_OVERRIDE_VAR
# multiple times for the same effect.
#
# If any subsequent configure commands set ${varname} and you wish to
# capture the resultant value into AM_${varname} in the case where
# ${varname} was _not_ provided at configure time, call
#
# AX_AM_OVERRIDE_FINALIZE
#
# after _all_ commands which might affect any of the variables specified
# in calls to AX_AM_OVERRIDE_VAR. This need be done only once, but
# repeated calls will not cause harm.
#
# There is a bit of trickery required to allow further manipulation of the
# AM_${varname} in a Makefile.am file. If AM_CFLAGS is used as is in a
# Makefile.am, e.g.
#
# libfoo_la_CFLAGS = $(AM_CFLAGS)
#
# then automake will emit code in Makefile.in which sets AM_CFLAGS from
# the configure'd value.
#
# If however, AM_CFLAGS is manipulated (i.e. appended to), you will have
# to explicitly arrange for the configure'd value to be substituted:
#
# AM_CFLAGS = @AM_CFLAGS@
# AM_CFLAGS += -lfoo
#
# or else automake will complain about using += before =.
#
# LICENSE
#
# Copyright (c) 2013 Smithsonian Astrophysical Observatory
# Copyright (c) 2013 Diab Jerius <djerius@cfa.harvard.edu>
#
# Copying and distribution of this file, with or without modification, are
# permitted in any medium without royalty provided the copyright notice
# and this notice are preserved. This file is offered as-is, without any
# warranty.
#serial 2
AC_DEFUN([_AX_AM_OVERRIDE_INITIALIZE],
[
m4_define([_mst_am_override_vars],[])
])
# _AX_AM_OVERRIDE_VAR(varname)
AC_DEFUN([_AX_AM_OVERRIDE_VAR],
[
m4_define([_mst_am_override_vars], m4_defn([_mst_am_override_vars]) $1 )
_mst_am_override_$1_set=false
AS_IF( [test "${$1+set}" = set],
[AC_SUBST([AM_$1],["$$1"])
$1=
_mst_am_override_$1_set=:
]
)
]) # _AX_AM_OVERRIDE_VAR
# _AX_AM_OVERRIDE_FINALIZE(varname)
AC_DEFUN([_AX_AM_OVERRIDE_FINALIZE],
[
AS_IF([$_mst_am_override_$1_set = :],
[],
[AC_SUBST([AM_$1],["$$1"])
$1=
_mst_am_override_$1_set=
]
)
AC_SUBST($1)
]) # _AX_AM_OVERRIDE_FINALIZE
AC_DEFUN([AX_AM_OVERRIDE_VAR],
[
AC_REQUIRE([_AX_AM_OVERRIDE_INITIALIZE])
m4_map_args_w([$1],[_AX_AM_OVERRIDE_VAR(],[)])
])# AX_OVERRIDE_VAR
# AX_AM_OVERRIDE_FINALIZE
AC_DEFUN([AX_AM_OVERRIDE_FINALIZE],
[
AC_REQUIRE([_AX_AM_OVERRIDE_INITIALIZE])
m4_map_args_w(_mst_am_override_vars,[_AX_AM_OVERRIDE_FINALIZE(],[)])
]) # AX_AM_OVERRIDE_FINALIZE
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