warn: allow aclocal to silence m4_require warnings

We introduce a new witness macro, m4_require_silent_probe, for use by
aclocal during the Autoconf-without-aclocal-m4 language.  This will let
aclocal process AC_CONFIG_MACRO_DIRS without emitting spurious warnings.
In fact, if aclocal doesn't suppress require warnings, then, when some macro
expanded in configure.ac calls AC_REQUIRE on another macro that is defined
in one of the local m4 macro dirs specified with AC_CONFIG_MACRO_DIRS, the
*first* autom4te invocation issued by aclocal, not yet being able to "see"
the m4 macro definitions in the local m4 dirs, will print spurious
warnings like:

    configure.ac:4: warning: MY_BAR is m4_require'd but not m4_defun'd
    configure.ac:3: MY_FOO is expanded from...

Expose the use of this macro in our testsuite.

Originally reported by Nick Bowler; see point (4) of:
<http://lists.gnu.org/archive/html/autoconf-patches/2012-11/msg00000.html>

* lib/m4sugar/m4sugar.m4 (_m4_require_call): Make warnings in the
-Wsyntax category depend on the witness macro.
* tests/m4sugar.at (m4@&t@_require: warning message): New test.
* doc/autoconf.texi (Prerequisite Macros): Document how aclocal
can silence AC_REQUIRE (m4_require) warnings.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/tests/m4sugar.at b/tests/m4sugar.at
index 997e2ddd..56927b90 100644
--- a/tests/m4sugar.at
+++ b/tests/m4sugar.at
@@ -429,6 +429,57 @@ autom4te: m4 failed with exit status: 1
 AT_CLEANUP
 
 
+## ----------------------------- ##
+## m4_require: warning message.  ##
+## ----------------------------- ##
+
+AT_SETUP([m4@&t@_require: warning message])
+AT_KEYWORDS([m4@&t@_require m4@&t@_require_silent_probe])
+
+# Mirror the job of aclocal on a typical scenario: the user invokes a
+# single macro that comes from one included file, which in turn requires
+# another macro from a second file.  When using the incomplete set of
+# files, we want a warning, unless we are merely learning which additional
+# macros are needed in order to regenerate the list of files to include.
+AT_DATA_M4SUGAR([script.4s],
+[[m4_init
+m4_include([script1.4s])
+foo
+]])
+
+AT_DATA_M4SUGAR([script1.4s],
+[[m4_defun([foo], [m4_require([bar])])
+]])
+
+AT_DATA_M4SUGAR([script2.4s],
+[[m4_defun([bar], [BAR])
+]])
+
+AT_CHECK_M4SUGAR([], [0], [],
+[[script.4s:3: warning: bar is m4@&t@_require'd but not m4@&t@_defun'd
+script1.4s:1: foo is expanded from...
+script.4s:3: the top level
+]])
+
+# Inline expansion of AT_CHECK_M4SUGAR, mirroring how aclocal will
+# inject a definition of our witness macro for a silent run.
+echo 'm4@&t@_define([m4@&t@_require_silent_probe])' |
+  AT_CHECK_AUTOM4TE([--language=m4sugar - script.4s -o script],
+[0], [], [])
+
+# Now that we have recomputed the set of include files, things should work.
+AT_DATA_M4SUGAR([script.4s],
+[[m4_init
+m4_include([script1.4s])
+m4_include([script2.4s])
+foo
+]])
+
+AT_CHECK_M4SUGAR([], [0], [], [])
+
+AT_CLEANUP
+
+
 ## ----------------------------------- ##
 ## m4_require: circular dependencies.  ##
 ## ----------------------------------- ##