bug in perl autoscan

I just installed autoscan version 2.21 (on guixSD), and it gave me this
warning in a recently un-tar-ed linphone.tar.gz directory.

#BEGIN_SRC sh
  autoscan
#END_SRC

    Unescaped left brace in regex is deprecated here (and will be fatal in Perl 5.30), passed through in regex; marked by <-- HERE in m/\${ <-- HERE [^\}]*}/ at /home/joshua/.guix-profile/bin/autoscan line 361.
    configure.ac: warning: missing AC_CHECK_FUNCS([__argz_count]) wanted by: intl/l10nflist.c:323
    configure.ac: warning: missing AC_CHECK_FUNCS([__argz_next]) wanted by: intl/l10nflist.c:371
    configure.ac: warning: missing AC_CHECK_FUNCS([__argz_stringify]) wanted by: intl/l10nflist.c:248
    configure.ac: warning: missing AC_CHECK_FUNCS([atexit]) wanted by: gtk/chat.c:54
    configure.ac: warning: missing AC_CHECK_FUNCS([dup2]) wanted by: console/shell.c:195
    configure.ac: warning: missing AC_CHECK_FUNCS([inet_ntoa]) wanted by: coreapi/misc.c:415
    configure.ac: warning: missing AC_CHECK_FUNCS([localtime_r]) wanted by: gtk/main.c:852
    configure.ac: warning: missing AC_CHECK_FUNCS([memmove]) wanted by: coreapi/linphonecall.c:4770
    configure.ac: warning: missing AC_CHECK_FUNCS([mempcpy]) wanted by: intl/localealias.c:213
    configure.ac: warning: missing AC_CHECK_FUNCS([memset]) wanted by: gtk/status_notifier.c:458
    configure.ac: warning: missing AC_CHECK_FUNCS([mkdir]) wanted by: gtk/logging.c:103
    configure.ac: warning: missing AC_CHECK_FUNCS([munmap]) wanted by: intl/loadmsgcat.c:1005
    configure.ac: warning: missing AC_CHECK_FUNCS([nl_langinfo]) wanted by: coreapi/sqlite3_bctbx_vfs.c:272
    configure.ac: warning: missing AC_CHECK_FUNCS([pow]) wanted by: coreapi/linphonecall.c:2859
    configure.ac: warning: missing AC_CHECK_FUNCS([putenv]) wanted by: intl/cat-compat.c:199
    configure.ac: warning: missing AC_CHECK_FUNCS([realpath]) wanted by: coreapi/lpconfig.c:103
    configure.ac: warning: missing AC_CHECK_FUNCS([regcomp]) wanted by: coreapi/account_creator.c:262
    configure.ac: warning: missing AC_CHECK_FUNCS([setenv]) wanted by: intl/cat-compat.c:196
    configure.ac: warning: missing AC_CHECK_FUNCS([setlocale]) wanted by: gtk/main.c:2187
    configure.ac: warning: missing AC_CHECK_FUNCS([socket]) wanted by: coreapi/misc.c:296
    configure.ac: warning: missing AC_CHECK_FUNCS([strcasecmp]) wanted by: gtk/friendlist.c:645
    configure.ac: warning: missing AC_CHECK_FUNCS([strchr]) wanted by: gtk/support.c:218
    configure.ac: warning: missing AC_CHECK_FUNCS([strcspn]) wanted by: intl/loadmsgcat.c:800
    configure.ac: warning: missing AC_CHECK_FUNCS([strdup]) wanted by: gtk/main.c:196
    configure.ac: warning: missing AC_CHECK_FUNCS([strerror]) wanted by: gtk/singleinstance.c:82
    configure.ac: warning: missing AC_CHECK_FUNCS([strncasecmp]) wanted by: tools/generator.cc:213
    configure.ac: warning: missing AC_CHECK_FUNCS([strpbrk]) wanted by: coreapi/linphonecore.c:993
    configure.ac: warning: missing AC_CHECK_FUNCS([strrchr]) wanted by: gtk/main.c:198
    configure.ac: warning: missing AC_CHECK_FUNCS([strstr]) wanted by: gtk/support.c:144
    configure.ac: warning: missing AC_CHECK_FUNCS([strtol]) wanted by: console/linphonec.c:1292
    configure.ac: warning: missing AC_CHECK_FUNCS([strtoull]) wanted by: coreapi/proxy.c:174
    configure.ac: warning: missing AC_CHECK_HEADERS([argz.h]) wanted by: intl/l10nflist.c:33
    configure.ac: warning: missing AC_CHECK_HEADERS([fcntl.h]) wanted by: console/wav2raw.c:8
    configure.ac: warning: missing AC_CHECK_HEADERS([langinfo.h]) wanted by: intl/loadmsgcat.c:61
    configure.ac: warning: missing AC_CHECK_HEADERS([libintl.h]) wanted by: gtk/linphone.h:58
    configure.ac: warning: missing AC_CHECK_HEADERS([limits.h]) wanted by: build/wp8/zlib/zconf.h:397
    configure.ac: warning: missing AC_CHECK_HEADERS([locale.h]) wanted by: gtk/main.c:55
    configure.ac: warning: missing AC_CHECK_HEADERS([malloc.h]) wanted by: intl/cat-compat.c:30
    configure.ac: warning: missing AC_CHECK_HEADERS([netdb.h]) wanted by: console/linphonec.c:51
    configure.ac: warning: missing AC_CHECK_HEADERS([nl_types.h]) wanted by: intl/cat-compat.c:35
    configure.ac: warning: missing AC_CHECK_HEADERS([stddef.h]) wanted by: build/wp8/zlib/zconf.h:435
    configure.ac: warning: missing AC_CHECK_HEADERS([stdio_ext.h]) wanted by: intl/localealias.c:33
    configure.ac: warning: missing AC_CHECK_HEADERS([sys/ioctl.h]) wanted by: daemon/daemon.cc:22
    configure.ac: warning: missing AC_CHECK_HEADERS([sys/socket.h]) wanted by: console/linphonec.c:49
    configure.ac: warning: missing AC_CHECK_HEADERS([sys/time.h]) wanted by: console/linphonec.c:50
    configure.ac: warning: missing AC_CHECK_HEADERS([wchar.h]) wanted by: include/MSVC/stdint.h:52
    configure.ac: warning: missing AC_CHECK_HEADER_STDBOOL wanted by: wrappers/cpp/object.cc:63
    configure.ac: warning: missing AC_FUNC_ALLOCA wanted by: intl/localealias.c:42
    configure.ac: warning: missing AC_FUNC_FORK wanted by: console/shell.c:179
    configure.ac: warning: missing AC_FUNC_MALLOC wanted by: wrappers/cpp/object.cc:49
    configure.ac: warning: missing AC_FUNC_MKTIME wanted by: coreapi/call_log.c:53
    configure.ac: warning: missing AC_FUNC_MMAP wanted by: intl/loadmsgcat.c:953
    configure.ac: warning: missing AC_FUNC_REALLOC wanted by: intl/localealias.c:312
    configure.ac: warning: missing AC_PATH_X wanted by: console/linphonec.c:74
    configure.ac: warning: missing AC_PROG_RANLIB wanted by: ltmain.sh:3772
    configure.ac: warning: missing AC_PROG_YACC wanted by: intl/Makefile.in:51
    configure.ac: warning: missing AC_TYPE_INT16_T wanted by: include/MSVC/stdint.h:76
    configure.ac: warning: missing AC_TYPE_INT32_T wanted by: include/MSVC/stdint.h:77
    configure.ac: warning: missing AC_TYPE_INT64_T wanted by: include/linphone/dictionary.h:45
    configure.ac: warning: missing AC_TYPE_INT8_T wanted by: include/MSVC/stdint.h:75
    configure.ac: warning: missing AC_TYPE_OFF_T wanted by: coreapi/sqlite3_bctbx_vfs.c:80
    configure.ac: warning: missing AC_TYPE_PID_T wanted by: gtk/status_notifier.c:30
    configure.ac: warning: missing AC_TYPE_SIZE_T wanted by: gtk/update.c:26
    configure.ac: warning: missing AC_TYPE_SSIZE_T wanted by: coreapi/misc.c:399
    configure.ac: warning: missing AC_TYPE_UINT16_T wanted by: include/MSVC/stdint.h:79
    configure.ac: warning: missing AC_TYPE_UINT32_T wanted by: include/linphone/chat.h:261
    configure.ac: warning: missing AC_TYPE_UINT64_T wanted by: include/linphone/call_stats.h:104
    configure.ac: warning: missing AC_TYPE_UINT8_T wanted by: gtk/singleinstance.c:66

A wise person an the guix mailing list told me this, when I showed him
the error:
 
The regexp in question is

      s/\${[^\}]*}//g;

Perl is complaining because perl regexp use curly braces to specify a range of valid repeats.
Maybe the easiest way to understand it is that the following equivalences hold in regexps:

? is equivalent to {0,1}
+ is equivalent to {1,}
* is equivalent to {0,}

The above (at the end of the regexp "\${[^\}]*}") probably means a literal curly
brace--but they don't escape it - hence the warning.

It's only a warning because no valid repeat range can start with a closing curly
brace.
So perl can still figure out what you meant.

But it's obviously not recommended to use unescaped closing curly braces to
match a literal closing curly brace regardless.

Thanks,

-- 
Joshua Branson
Sent from Emacs and Gnus