dnl CF_FIND_LINKAGE version: 22 updated: 2020/12/31 20:19:42
dnl ---------------
dnl Find a library (specifically the linkage used in the code fragment),
dnl searching for it if it is not already in the library path.
dnl See also CF_ADD_SEARCHPATH.
dnl
dnl Parameters (4-on are optional):
dnl     $1 = headers for library entrypoint
dnl     $2 = code fragment for library entrypoint
dnl     $3 = the library name without the "-l" option or ".so" suffix.
dnl     $4 = action to perform if successful (default: update CPPFLAGS, etc)
dnl     $5 = action to perform if not successful
dnl     $6 = module name, if not the same as the library name
dnl     $7 = extra libraries
dnl
dnl Sets these variables:
dnl     $cf_cv_find_linkage_$3 - yes/no according to whether linkage is found
dnl     $cf_cv_header_path_$3 - include-directory if needed
dnl     $cf_cv_library_path_$3 - library-directory if needed
dnl     $cf_cv_library_file_$3 - library-file if needed, e.g., -l$3
AC_DEFUN([CF_FIND_LINKAGE],[

# If the linkage is not already in the $CPPFLAGS/$LDFLAGS configuration, these
# will be set on completion of the AC_TRY_LINK below.
cf_cv_header_path_$3=
cf_cv_library_path_$3=

CF_MSG_LOG([Starting [FIND_LINKAGE]($3,$6)])

cf_save_LIBS="$LIBS"

AC_TRY_LINK([$1],[$2],[
	cf_cv_find_linkage_$3=yes
	cf_cv_header_path_$3=/usr/include
	cf_cv_library_path_$3=/usr/lib
],[

LIBS="-l$3 $7 $cf_save_LIBS"

AC_TRY_LINK([$1],[$2],[
	cf_cv_find_linkage_$3=yes
	cf_cv_header_path_$3=/usr/include
	cf_cv_library_path_$3=/usr/lib
	cf_cv_library_file_$3="-l$3"
],[
	cf_cv_find_linkage_$3=no
	LIBS="$cf_save_LIBS"

	CF_VERBOSE(find linkage for $3 library)
	CF_MSG_LOG([Searching for headers in [FIND_LINKAGE]($3,$6)])

	cf_save_CPPFLAGS="$CPPFLAGS"
	cf_test_CPPFLAGS="$CPPFLAGS"

	CF_HEADER_PATH(cf_search,ifelse([$6],,[$3],[$6]))
	for cf_cv_header_path_$3 in $cf_search
	do
		if test -d "$cf_cv_header_path_$3" ; then
			CF_VERBOSE(... testing $cf_cv_header_path_$3)
			CPPFLAGS="$cf_save_CPPFLAGS"
			CF_APPEND_TEXT(CPPFLAGS,-I$cf_cv_header_path_$3)
			AC_TRY_COMPILE([$1],[$2],[
				CF_VERBOSE(... found $3 headers in $cf_cv_header_path_$3)
				cf_cv_find_linkage_$3=maybe
				cf_test_CPPFLAGS="$CPPFLAGS"
				break],[
				CPPFLAGS="$cf_save_CPPFLAGS"
				])
		fi
	done

	if test "$cf_cv_find_linkage_$3" = maybe ; then

		CF_MSG_LOG([Searching for $3 library in [FIND_LINKAGE]($3,$6)])

		cf_save_LIBS="$LIBS"
		cf_save_LDFLAGS="$LDFLAGS"

		ifelse([$6],,,[
		CPPFLAGS="$cf_test_CPPFLAGS"
		LIBS="-l$3 $7 $cf_save_LIBS"
		AC_TRY_LINK([$1],[$2],[
			CF_VERBOSE(... found $3 library in system)
			cf_cv_find_linkage_$3=yes])
			CPPFLAGS="$cf_save_CPPFLAGS"
			LIBS="$cf_save_LIBS"
			])

		if test "$cf_cv_find_linkage_$3" != yes ; then
			CF_LIBRARY_PATH(cf_search,$3)
			for cf_cv_library_path_$3 in $cf_search
			do
				if test -d "$cf_cv_library_path_$3" ; then
					CF_VERBOSE(... testing $cf_cv_library_path_$3)
					CPPFLAGS="$cf_test_CPPFLAGS"
					LIBS="-l$3 $7 $cf_save_LIBS"
					LDFLAGS="$cf_save_LDFLAGS -L$cf_cv_library_path_$3"
					AC_TRY_LINK([$1],[$2],[
					CF_VERBOSE(... found $3 library in $cf_cv_library_path_$3)
					cf_cv_find_linkage_$3=yes
					cf_cv_library_file_$3="-l$3"
					break],[
					CPPFLAGS="$cf_save_CPPFLAGS"
					LIBS="$cf_save_LIBS"
					LDFLAGS="$cf_save_LDFLAGS"
					])
				fi
			done
			CPPFLAGS="$cf_save_CPPFLAGS"
			LDFLAGS="$cf_save_LDFLAGS"
		fi

	else
		cf_cv_find_linkage_$3=no
	fi
	],$7)
])

LIBS="$cf_save_LIBS"

if test "$cf_cv_find_linkage_$3" = yes ; then
ifelse([$4],,[
	CF_ADD_INCDIR($cf_cv_header_path_$3)
	CF_ADD_LIBDIR($cf_cv_library_path_$3)
	CF_ADD_LIB($3)
],[$4])
else
ifelse([$5],,AC_MSG_WARN(Cannot find $3 library),[$5])
fi
])dnl
