Warn if AC_INIT or AC_OUTPUT are missing from configure.ac (#107986)

It is almost always incorrect for a configure script to omit either
AC_INIT or AC_OUTPUT.  Issue warnings in the ‘syntax’ category for
this.

The implementation is, unfortunately, a bit of a kludge.  To check for
the _absence_ of a macro invocation, we can use m4_provide_if inside a
m4_wrap hook.  However, if we activate the m4_wrap hook directly from
general.m4, we get spurious warnings at freeze time.  We also get
warnings whenever a script that’s missing AC_INIT and/or AC_OUTPUT
is *traced*, which means we get double warnings from autoconf, and
autoheader and aclocal complain about it too, which seems unnecessary.

A clean way to deal with this would be to make the hook look for a
special macro that’s defined only when autoconf (the program) is
invoked without any --trace arguments.  Unfortunately, autom4te
doesn’t pass --define down to M4, and changing that would involve
coordinating with Automake (the project), so instead I’ve gone for the
kludge: a new file lib/autoconf/trailer.m4 that calls m4_wrap.  This
file is *not* included in autoconf.m4f, but it’s installed, and it’s
added to the m4 invocation by autoconf (the program) only when not
tracing.  (It still uses m4_wrap, because we pass it to m4 *before*
configure.ac, because otherwise we get nonsense locations for any
*other* diagnostics coming out of this autoconf invocation.  I don’t
know why.)

The additional checks in autoreconf are intended to make sure that if
autoreconf skips a directory entirely, you get told why.

Lots of tests in the testsuite didn’t bother with AC_OUTPUT, and
somewhat fewer didn’t bother with AC_INIT; where possible I just added
them.

Suggested by David A. Wheeler, who submitted a patch, but I didn’t
wind up using any of his code.  (His implementation used an extra
tracing pass, only checked for a missing AC_INIT, and invented a new
command-line option to turn off this specific warning.  I thought this
was tidier overall, despite the kludge.)

* lib/autoconf/general.m4 (_AC_FINALIZE): New macro: code to be run
  when generating configure, after the entire configure.ac is
  processed. Currently only checks that AC_INIT and AC_OUTPUT were
  called at some point, issuing syntax-category warnings if not.
  (AC_INIT, AC_OUTPUT): m4_provide self.
* lib/autoconf/trailer.m4: New file that just calls m4_wrap([_AC_FINALIZE]).
* lib/local.mk: Install new file.

* bin/autoconf.as: Add trailer.m4 to the final invocation of autom4te,
  but only when not tracing.
* bin/autoreconf.in (autoreconf_current_directory): Distinguish in
  diagnostics between “directory skipped because it doesn’t have a
  configure.ac or configure.in” (e.g. Cygnus configure) and “directory
  has a configure.ac but it doesn’t appear to be autoconf input.”

* tests/*.at: Fix all tests affected by the new warnings.

1 files changed, 26 insertions, 7 deletions

diff --git a/tests/base.at b/tests/base.at
index 98125173..4042a8aa 100644
--- a/tests/base.at
+++ b/tests/base.at
@@ -57,7 +57,10 @@ test -z "$test1" &&
 AS_EXIT(0)
 ]])
 
-AT_CHECK_AUTOCONF
+AT_CHECK_AUTOCONF([], [0], [],
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+]])
 AT_CHECK_CONFIGURE
 
 AT_CLEANUP
@@ -117,7 +120,10 @@ case $multi_test:$single_test in
 esac
 ]])
 
-AT_CHECK_AUTOCONF([], 0, [])
+AT_CHECK_AUTOCONF([], 0, [],
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+]])
 
 AT_CHECK_CONFIGURE
 
@@ -160,7 +166,10 @@ case $multi_test:$single_test in
 esac
 ]])
 
-AT_CHECK_AUTOCONF([], 0, [])
+AT_CHECK_AUTOCONF([], 0, [],
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+]])
 AT_CHECK_CONFIGURE
 
 AT_CLEANUP
@@ -192,7 +201,10 @@ case $inner_test in
 esac
 ]])
 
-AT_CHECK_AUTOCONF
+AT_CHECK_AUTOCONF([], 0, [],
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+]])
 AT_CHECK_CONFIGURE
 
 AT_CLEANUP
@@ -208,6 +220,7 @@ AT_SETUP([AC_INIT])
 
 AT_DATA([configure.ac],
 [[AC_INIT([GNU fu], [1.0], [bug-fu@gnu.org])
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF
@@ -354,6 +367,7 @@ words that may be matched by scanners for legal things,
 causing extra work for distributors.
 Multi-line values should be supported.
 ]])
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF
@@ -403,8 +417,7 @@ if ${my_cv_variable+false} :; then
   AC_MSG_ERROR([AC@&@&t@t@_CACHE_VAL did not ensure that the cache variable was set])
 fi
 
-# AC_CACHE_SAVE should be enough here, no need for AC_OUTPUT.
-AC_CACHE_SAVE
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF([], [], [], [stderr])
@@ -603,6 +616,7 @@ AC_COMPUTE_INT([invalid_expression],
 	       [invalid_expression=failed])
 test "$invalid_expression" = failed ||
   AC_MSG_ERROR([**0** evaluated to $invalid_expression instead of failing])
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF
@@ -633,6 +647,8 @@ if AC_TRY_COMMAND([(echo "The Cat in the Hat";
 		   grep \^The\ Hat\ in\ the\ Cat\$ >/dev/null]); then
   AC_MSG_ERROR([saw the Hat in the Cat])
 fi
+
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF
@@ -650,9 +666,10 @@ AT_SETUP([Input/Output])
 AT_DATA([configure.ac],
 [[AC_INIT
 cat <&AS@&t@_ORIGINAL_STDIN_FD >&AS@&t@_MESSAGE_FD
+AC_OUTPUT
 ]])
 AT_CHECK_AUTOCONF
-AT_CHECK([echo Hello | CONFIG_SITE=/dev/null ./configure $configure_options | grep -v 'configure: loading site script '],, [Hello
+AT_CHECK([echo Hello | CONFIG_SITE=/dev/null ./configure $configure_options | grep -v '^configure: '],, [Hello
 ])
 AT_CHECK([echo Hello | CONFIG_SITE=/dev/null ./configure $configure_options --silent])
 
@@ -668,6 +685,7 @@ AT_SETUP([configure arguments])
 AT_DATA([configure.ac],
 [[AC_INIT
 echo "$@"
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF
@@ -706,6 +724,7 @@ AC_ARG_ENABLE([c++],
 echo "use_foo: $use_foo"
 echo "with_c++: $with_c__, $choice_with"
 echo "enable_c++: $enable_c__, $choice_enable"
+AC_OUTPUT
 ]])
 
 AT_CHECK_AUTOCONF