You should also look carefully at the existing set of autoupdate tests (tests/tools.at, "autoupdate" section), especially the ones marked as expected to fail.

Another one, which falls into the nested category: a quote was stripped, leaving the result unbalanced:

@@ -3618,17 +3578,14 @@ if test "$wx_cv_size_t_is_uint" = "yes"; then
 else
     AC_CACHE_CHECK([if size_t is unsigned long], [
         wx_cv_size_t_is_ulong, [
-        AC_TRY_COMPILE([#include <stddef.h>],
-            [
+        AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <stddef.h>]], [[
                 return 0; }

                 struct Foo { void foo(size_t); void foo(unsigned long); };

                 int bar() {
-            ],
-            wx_cv_size_t_is_ulong=no,
-            wx_cv_size_t_is_ulong=yes
-        )
+            ]])],[wx_cv_size_t_is_ulong=no],[wx_cv_size_t_is_ulong=yes
+        ])
     )]

     if test "$wx_cv_size_t_is_ulong" = "yes"; then

Hi Zack,

Thanks for the prompt feedback.

Another issue I've found is that the mishandling of 'dnl' comments; they are often added into the argument itself, breaking for example this AC_TRY_RUN at configure time:

@@ -2200,9 +2188,8 @@ if test "$wxUSE_ZLIB" != "no" ; then
         dnl has anything more ancient (1.1.3 was released in July 1998)
         dnl anyhow
         AC_CACHE_CHECK([for zlib.h >= 1.1.4], ac_cv_header_zlib_h,
-            [AC_TRY_RUN(
-                dnl zlib.h defines ZLIB_VERSION="x.y.z"
-                [
+            [AC_RUN_IFELSE([AC_LANG_SOURCE([[dnl zlib.h defines ZLIB_VERSION="x.y.z"
+
                     #include <zlib.h>
                     #include <stdio.h>
                     #include <stdlib.h>
@@ -2218,12 +2205,7 @@ if test "$wxUSE_ZLIB" != "no" ; then
                                  ZLIB_VERSION[4] >= '4')) ? "yes" : "no");
                         return 0;
                     }
-                ],
-                ac_cv_header_zlib_h=`cat conftestval`,
-                ac_cv_header_zlib_h=no,
-                dnl cross-compiling: don't have an answer, try later
-                unset ac_cv_header_zlib_h
-            )]
+                ]])],[ac_cv_header_zlib_h=`cat conftestval`],[ac_cv_header_zlib_h=no],[dnl cross-compiling: don't have an answer])]
         )
         dnl If the test above did not come up with a value (e.g. cross
         dnl compiling) then this should give a definitive answer

Which results in the config.log to:

conftest.c:43:1: error: unknown type name 'dnl'
   43 | dnl zlib.h defines ZLIB_VERSION="x.y.z"
      | ^~~
conftest.c:43:9: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
   43 | dnl zlib.h defines ZLIB_VERSION="x.y.z"
      |         ^

I understand redesigning to fix the root of these problems may take a long time to fix (or never happen).  I may take a peek myself if I find the time.

Cheers,

Maxim

Hi,

I've been trying to use autoupdate on the wxWidgets project [0]

[0]  https://github.com/wxWidgets/wxWidgets

It's a good test, being a 8k lines file apparently last updated for Autoconf 2.59.

After fixing a couple of quoting problems with the help of Alfred (ams), I was able to have it run once happily.  The problem is that the output it produces then trips it when running again; in other words, it produces a broken configure.ac file.

It seems the problem has to do with the _au_m4_changequote([,]) it generates, that are placed before nested AC_TRY_COMPILE or AC_TRY_LINK usages.

Attaches are the Git patches of my debugging session and recorded observations / edits.  They can be applied to wxWidgets at commit 1093bb492bc90531162490ba1711f9dba09f59e0.

Here's the first hunk of the recorded 'autoupdate broken substitutions', for example:

modified   configure.in
@@ -1407,12 +1407,10 @@ dnl This case is for OS X vs. everything else
 case "${host}" in
   --darwin* )
     AC_MSG_CHECKING([if CoreFoundation/CFBase.h is usable])
-    AC_TRY_COMPILE([#include <CoreFoundation/CFBase.h>
-],[],
-        [AC_MSG_RESULT([yes])],
-        [AC_MSG_RESULT([no])
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <CoreFoundation/CFBase.h>
+]], [[]])],[AC_MSG_RESULT([yes])],[AC_MSG_RESULT([no])
         AC_MSG_CHECKING([if _CF_USE_FRAMEWORK_INCLUDES_ is required])
-        AC_TRY_COMPILE([#define _CF_USE_FRAMEWORK_INCLUDES_
+        au_m4_changequote([,])AC_TRY_COMPILE([#define __CF_USE_FRAMEWORK_INCLUDES_
 #include <CoreFoundation/CFBase.h>
         ],[],
         [AC_MSG_RESULT([yes])
@@ -1421,8 +1419,8 @@ case "${host}" in
         CPPFLAGS="-D__CF_USE_FRAMEWORK_INCLUDES__ $CPPFLAGS"],
         [AC_MSG_FAILURE([no.  CoreFoundation not available.])]
         )
-        ]
-    )
+       
+    ])
   ;;
 esac

You can replay the patches on the mentioned wxWidgets commit above and see for yourself.  My testing was done using Autoconf 2.71 from GNU Guix at commit 3fc26c6dc4b6bbf558a17b5e3ef8092ea0eeeacd.

I hope that my report is actionable!  Thank you for maintaining this important (and probably a bit hairy at places) tool.