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, 23 insertions, 5 deletions

diff --git a/tests/tools.at b/tests/tools.at
index 314462ff..3093225c 100644
--- a/tests/tools.at
+++ b/tests/tools.at
@@ -390,6 +390,7 @@ AT_DATA([configure.ac],
 [[AC_INIT
 AC_CONFIG_MACRO_DIR([dir1])
 AC_CONFIG_MACRO_DIR([dir2])
+AC_OUTPUT
 ]])
 AT_CHECK_AUTOCONF([], [1], [], [stderr])
 AT_CHECK([grep 'error: AC_CONFIG_MACRO_DIR can only be used once' stderr],
@@ -421,6 +422,7 @@ AT_DATA([configure.ac],
 [[AC_INIT
 AC_CONFIG_MACRO_DIRS([dir1])
 AC_CONFIG_MACRO_DIRS([dir2])
+AC_OUTPUT
 ]])
 AT_CHECK_AUTOCONF([], [0], [], [])
 AT_CHECK_AUTOCONF([-t AC_CONFIG_MACRO_DIR], [0],
@@ -459,7 +461,9 @@ end-language: "Autoconf-without-aclocal-m4"
 ]])
 
 AT_CHECK_AUTOCONF([], 1, [],
-[[configure.ac:2: error: possibly undefined macro: m4@&t@_foo
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+configure.ac:2: error: possibly undefined macro: m4@&t@_foo
       If this token and others are legitimate, please use m4@&t@_pattern_allow.
       See the Autoconf documentation.
 configure.ac:3: error: possibly undefined macro: _m4@&t@_bar
@@ -467,8 +471,12 @@ configure.ac:4: error: possibly undefined macro: AS@&t@_FOO
 configure.ac:5: error: possibly undefined macro: _AS@&t@_BAR
 configure.ac:6: error: possibly undefined macro: d@&t@nl
 ]])
-# Second run should succeed and yield no output.
-AT_CHECK([autoconf])
+# A second run (without --force) should succeed and yield only the
+# warnings about AC_INIT and AC_OUTPUT.
+AT_CHECK_M4([autoconf], 0, [],
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+]])
 
 AT_CLEANUP
 
@@ -500,7 +508,9 @@ It would be very bad if Autoconf forgot to expand [AS_]INIT!
 ]])
 
 AT_CHECK_AUTOCONF([], 1, [],
-[[configure.ac:1: error: possibly undefined macro: AS@&t@_INIT
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+configure.ac:1: error: possibly undefined macro: AS@&t@_INIT
       If this token and others are legitimate, please use m4@&t@_pattern_allow.
       See the Autoconf documentation.
 configure.ac:7: error: possibly undefined macro: AS@&t@_ALLOWED_NOT
@@ -539,7 +549,10 @@ m4_divert([])dnl
  line that begins with a space
 ]])
 
-AT_CHECK_AUTOCONF
+AT_CHECK_AUTOCONF([], 0, [],
+[[trailer.m4: warning: AC_INIT was never used
+trailer.m4: warning: AC_OUTPUT was never used
+]])
 
 AT_CLEANUP
 
@@ -1009,6 +1022,7 @@ AT_DATA([configure.ac],
 [[AC_INIT
 OLD(1, 2)
 NEW([0, 0], [0])
+AC_OUTPUT
 ]])
 
 # Checking `autoupdate'.
@@ -1053,6 +1067,7 @@ AT_SETUP([autoupdating AC_HELP_STRING])
 AT_DATA([configure.ac],
 [[AC_INIT
 AC_ARG_ENABLE([foo], [AC_HELP_STRING([--enable-foo], [foo bar])], [:], [:])
+AC_OUTPUT
 ]])
 
 # Checking `autoupdate'.
@@ -1189,6 +1204,7 @@ AC_LANG_SAVE
 AC_LANG_RESTORE
 AC_LANG_SAVE
 AC_LANG_RESTORE
+AC_OUTPUT
 ]])
 
 # Checking `autoupdate'.
@@ -1210,6 +1226,7 @@ AT_DATA([aclocal.m4],
 AT_DATA([configure.ac],
 [[AC_INIT
 echo AC_FOREACH([myvar], [1 2 3], [' myvar'])OLD
+AC_OUTPUT
 ]])
 
 # Checking `autoupdate'.
@@ -1318,6 +1335,7 @@ chmod a-w sub
 
 AT_DATA([configure.ac],
 [[AC_INIT
+AC_OUTPUT
 ]])
 
 AT_DATA([.autom4te.cfg],