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.

2 files changed, 23 insertions, 5 deletions

diff --git a/bin/autoconf.as b/bin/autoconf.as
index 581eb81e..ab6e3c52 100644
--- a/bin/autoconf.as
+++ b/bin/autoconf.as
@@ -85,6 +85,7 @@ exit_missing_arg='
 
 # Variables.
 : ${AUTOM4TE='@bindir@/@autom4te-name@'}
+: ${trailer_m4='@pkgdatadir@/autoconf/trailer.m4'}
 autom4te_options=
 outfile=
 verbose=false
@@ -183,9 +184,20 @@ esac
 # Unless specified, the output is stdout.
 test -z "$outfile" && outfile=-
 
+# Don't read trailer.m4 if we are tracing.
+if test -n "$traces"; then
+    trailer_m4=""
+else
+    # The extra quotes will be stripped by eval.
+    trailer_m4=\""$trailer_m4"\"
+fi
+
 # Run autom4te with expansion.
+# trailer.m4 is read _before_ $infile, despite the name,
+# because putting it afterward screws up autom4te's location tracing.
 eval set x "$autom4te_options" \
-  --language=autoconf --output=\"\$outfile\" "$traces" \"\$infile\"
+  --language=autoconf --output=\"\$outfile\" "$traces" \
+  $trailer_m4 \"\$infile\"
 shift
 $verbose && AS_ECHO(["$as_me: running $AUTOM4TE $*"]) >&2
 exec "$AUTOM4TE" "$@"
diff --git a/bin/autoreconf.in b/bin/autoreconf.in
index 12806d3a..1ca11f28 100644
--- a/bin/autoreconf.in
+++ b/bin/autoreconf.in
@@ -245,8 +245,9 @@ sub parse_args ()
 
 # &autoreconf_current_directory
 # -----------------------------
-sub autoreconf_current_directory ()
+sub autoreconf_current_directory ($)
 {
+  my ($directory) = @_;
   my $configure_ac = find_configure_ac;
 
   # ---------------------- #
@@ -266,10 +267,15 @@ sub autoreconf_current_directory ()
 	  # See below for why we look for gettext here.
 	  $uses_gettext = 1  if /^AM_GNU_GETTEXT_VERSION/;
 	}
+      if (!$uses_autoconf)
+        {
+          error "$configure_ac: AC_INIT not found; not an autoconf script?";
+          return;
+        }
     }
-  if (!$uses_autoconf)
+  else
     {
-      verb "$configure_ac: not using Autoconf";
+      verb "neither configure.ac nor configure.in present in $directory";
       return;
     }
 
@@ -598,7 +604,7 @@ sub autoreconf ($)
   chdir $directory
     or error "cannot chdir to $directory: $!";
 
-  autoreconf_current_directory;
+  autoreconf_current_directory ($directory);
 
   # The format is not free: taken from Emacs, itself using GNU Make's
   # format.