[PATCH v3 1/4] AC_CHECK_FUNCS_ONCE: honor current AC_LANG

[Eric Blake]

Previously, AC_CHECK_FUNCS_ONCE collected a list of function names
to check, but ran the checks using the AC_LANG that was active
during the first encounter of the macro.  In practice, this is
usually the C language, and we haven't had actual reports of projects
attempting to use AC_CHECK_FUNCS_ONCE across multiple languages,
rather this was discovered by code inspection.

With this patch, the code now tracks a separate per-language list of
names to check.  Note, however, that it is only possible to check for
a given function name in one language; attempting to add a name again
under AC_CHECK_FUNCS_ONCE while a different language is active is a
no-op (this still makes sense because the side-effect of defining
the CPP macro HAVE_FUNC does not include a language prefix).

* lib/autoconf/functions.m4 (_AC_CHECK_FUNC_ONCE)
(_AC_FUNCS_EXPANSION):
* NEWS: Mention it.

Signed-off-by: Eric Blake <address@hidden>
---
 NEWS                      |  4 ++++
 lib/autoconf/functions.m4 | 17 +++++++++--------
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/NEWS b/NEWS
index a4c53dd..532e15e 100644
--- a/NEWS
+++ b/NEWS
@@ -111,6 +111,10 @@ GNU Autoconf NEWS - User visible changes.
   useful effect is to trigger those checks, with this macro.  It is
   unlikely to be useful otherwise.

+- The AC_CHECK_FUNCS_ONCE macro now supports use with multiple
+  languages, rather than forcing all checks in the language used by
+  the first encounter of the macro.
+
 ** Man pages for config.guess and config.sub are no longer provided.
 They were moved to the master source tree for config.guess and config.sub.

diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index 66abe29..7b98a06 100644
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -96,9 +96,9 @@ AC_DEFUN([AC_CHECK_FUNCS],
 # -----------------------------
 # Check for a single FUNCTION once.
 m4_define([_AC_CHECK_FUNC_ONCE],
-[_AH_CHECK_FUNC([$1])AC_DEFUN([_AC_Func_$1],
-  [m4_divert_text([INIT_PREPARE], [AS_VAR_APPEND([ac_func_list], [" $1"])])
-_AC_FUNCS_EXPANSION])AC_REQUIRE([_AC_Func_$1])])
+[_AH_CHECK_FUNC([$1])AC_DEFUN([_AC_Func_$1], [m4_divert_text([INIT_PREPARE],
+  [AS_VAR_APPEND([ac_func_]]_AC_LANG_ABBREV[[_list], [" $1"])])
+_AC_FUNCS_EXPANSION(_AC_LANG_ABBREV)])AC_REQUIRE([_AC_Func_$1])])

 # AC_CHECK_FUNCS_ONCE(FUNCTION...)
 # --------------------------------
@@ -107,12 +107,13 @@ _AC_FUNCS_EXPANSION])AC_REQUIRE([_AC_Func_$1])])
 AC_DEFUN([AC_CHECK_FUNCS_ONCE],
 [m4_map_args_w([$1], [_AC_CHECK_FUNC_ONCE(], [)])])

+# _AC_FUNCS_EXPANSION(LANG)
+# -------------------------
+# One-shot code per language LANG for checking all functions registered by
+# AC_CHECK_FUNCS_ONCE while that language was active.
 m4_define([_AC_FUNCS_EXPANSION],
-[
-  m4_divert_text([DEFAULTS], [ac_func_list=])
-  AC_CHECK_FUNCS([$ac_func_list])
-  m4_define([_AC_FUNCS_EXPANSION], [])
-])
+[m4_ifndef([$0($1)], [m4_define([$0($1)])m4_divert_text([DEFAULTS],
+[ac_func_$1_list=])AC_CHECK_FUNCS([$ac_func_$1_list])])])


 # _AC_REPLACE_FUNC(FUNCTION)
-- 
2.7.4