This errors in 4.4, did not in 4.2: set -u; declare -A foo; echo ${#foo[@]}

[David Linden]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-redhat-linux-gnu' 
-DCONF_VENDOR='redhat' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib  -D_GNU_SOURCE -DRECYCLES_PIDS 
-DDEFAULT_PATH_VALUE='/usr/local/bin:/usr/bin'  -DSYSLOG_HISTORY -O2 -g -pipe 
-Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS 
-fexceptions -fstack-protector-strong -grecord-gcc-switches 
-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 
-specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic 
-fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection 
-Wno-parentheses -Wno-format-security
uname output: Linux engdev2 4.18.0-553.22.1.el8_10.x86_64 #1 SMP Wed Sep 11 
18:02:00 EDT 2024 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-redhat-linux-gnu

Bash Version: 4.4
Patch Level: 20
Release Status: release

Description:
        This errors in 4.4, did not in 4.2: set -u; declare -A foo; echo 
${#foo[@]}
        How am I supposed to determine that a declared associative array is 
empty?
        Or even use it in a conditional even one where the value won't be 
evaluated?

Repeat-By:

        Bash 4.2:

                (21:10)$ bash --version; bash -c 'set -u; declare -A foo; echo 
${#foo[@]}; echo $((0 && ${#foo[@]}))'
                GNU bash, version 4.2.46(2)-release (x86_64-redhat-linux-gnu)
                Copyright (C) 2011 Free Software Foundation, Inc.
                License GPLv3+: GNU GPL version 3 or later 
http://gnu.org/licenses/gpl.html

                This is free software; you are free to change and redistribute 
it.
                There is NO WARRANTY, to the extent permitted by law.
>>>             0
>>>             0

        Bash 4.4:

                (21:14)$ bash --version; bash -c 'set -u; declare -A foo; echo 
${#foo[@]}'
                GNU bash, version 4.4.20(1)-release (x86_64-redhat-linux-gnu)
                Copyright (C) 2016 Free Software Foundation, Inc.
                License GPLv3+: GNU GPL version 3 or later 
http://gnu.org/licenses/gpl.html

                This is free software; you are free to change and redistribute 
it.
                There is NO WARRANTY, to the extent permitted by law.
>>>             bash: foo: unbound variable
                (21:14)$ bash --version; bash -c 'set -u; declare -A foo; echo 
$((0 && ${#foo[@]}))'
                GNU bash, version 4.4.20(1)-release (x86_64-redhat-linux-gnu)
                Copyright (C) 2016 Free Software Foundation, Inc.
                License GPLv3+: GNU GPL version 3 or later 
http://gnu.org/licenses/gpl.html

                This is free software; you are free to change and redistribute 
it.
                There is NO WARRANTY, to the extent permitted by law.
>>>             bash: foo: unbound variable

Perhaps related, ${#foo[@]:-0} is now considered a bad substitution; in 4.2 it 
was OK.