Path: csiph.com!goblin1!goblin.stu.neva.ru!usenet.stanford.edu!not-for-mail
From: andrej@podzimek.org
Newsgroups: gnu.bash.bug
Subject: Variable references (declare -n, "nameref") are limited to a depth of 8.
Date: Sat, 25 Apr 2020 08:55:11 +0200
Lines: 78
Approved: bug-bash@gnu.org
Message-ID: <mailman.1172.1587797724.3066.bug-bash@gnu.org>
References: <courier.000000005EA3DECF.0000B702@charon.podzimek.org>
NNTP-Posting-Host: lists.gnu.org
X-Trace: usenet.stanford.edu 1587797724 13324 209.51.188.17 (25 Apr 2020 06:55:24 GMT)
X-Complaints-To: action@cs.stanford.edu
To: bug-bash@gnu.org
Envelope-to: bug-bash@gnu.org
Received-SPF: pass client-ip=2a02:168:5cd0::; envelope-from=andrej@podzimek.org; helo=charon.podzimek.org
X-detected-operating-system: by eggs.gnu.org: Error: [-] PROGRAM ABORT : Malformed IPv6 address (bad octet value). Location : parse_addr6(), p0f-client.c:67
X-Received-From: 2a02:168:5cd0::
X-BeenThere: bug-bash@gnu.org
X-Mailman-Version: 2.1.23
Precedence: list
List-Id: Bug reports for the GNU Bourne Again SHell <bug-bash.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/bug-bash>, <mailto:bug-bash-request@gnu.org?subject=unsubscribe>
List-Archive: <https://lists.gnu.org/archive/html/bug-bash>
List-Post: <mailto:bug-bash@gnu.org>
List-Help: <mailto:bug-bash-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/bug-bash>, <mailto:bug-bash-request@gnu.org?subject=subscribe>
X-Mailman-Original-Message-ID: <courier.000000005EA3DECF.0000B702@charon.podzimek.org>
Xref: csiph.com gnu.bash.bug:16241

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -DDEFAULT_PATH_VALUE='/usr/local/sbin:/usr/local/bin:/usr/bin' -DSTANDARD_UTILS_PATH='/usr/bin' -DSYS_BASHRC='/etc/bash.bashrc' -DSYS_BASH_LOGOUT='/etc/bash.bash_logout' -DNON_INTERACTIVE_LOGIN_SHELLS -Wno-parentheses -Wno-format-security
uname output: Linux charon 5.6.4-arch1-1-user-regd #1 SMP PREEMPT Fri, 17 Apr 2020 12:06:27 +0000 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.0
Patch Level: 16
Release Status: release

Description:

  While looking for a way to share a "cache" array with a recursive function
  call stack (using local -n (nameref)), I hit a well-known problem with
  "circular name reference" (which has been around for a long time). The problem
  can be circumvented by renaming the variable twice per recursion level:

  recursive_function() {
    ...
    local -r cache_name="cache_${#FUNCNAME[@]}"
    local -n "$cache_name"="$1"
    local -n cache="$cache_name"
    ...
    recursive_function "$cache_name" 'other' 'arguments' ...
    ...
  }

  Now "${cache[@]}" references the shared variable under a consistent name,
  regardless call stack depth, and without the "circular name reference" issue.

  Sadly, this stops working at a certain (very small) call stack depth. There is
  no warning or error message; the ${cache[@]} just becomes empty unexpectedly.

  Importantly, this is also reproducible with a plain string variable and
  without any functions or (recursive) calls involved:

Repeat-By:

  previous=a
  declare ${previous}='This is set!'
  for var in {b..k}; do
    declare -n ${var}=${previous}
    previous="${var}"
  done
  for var in {a..k}; do
    echo "${var}: '${!var}'"
  done

Actual output:

  a: 'This is set!'
  b: 'This is set!'
  c: 'This is set!'
  d: 'This is set!'
  e: 'This is set!'
  f: 'This is set!'
  g: 'This is set!'
  h: 'This is set!'
  i: 'This is set!'
  j: ''
  k: ''

Expected output:

  a: 'This is set!'
  b: 'This is set!'
  c: 'This is set!'
  d: 'This is set!'
  e: 'This is set!'
  f: 'This is set!'
  g: 'This is set!'
  h: 'This is set!'
  i: 'This is set!'
  j: 'This is set!'
  k: 'This is set!'