'declare -i var=var' for var initially declared in calling scope

[Zachary Santer]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: msys
Compiler: gcc
Compilation CFLAGS: -march=nocona -msahf -mtune=generic -O2 -pipe
-D_STATIC_BUILD
uname output: MINGW64_NT-10.0-19045 Zack2021HPPavilion 3.5.3.x86_64
2024-06-03 06:22 UTC x86_64 Msys
Machine Type: x86_64-pc-msys

Bash Version: 5.2
Patch Level: 26
Release Status: release

Description:

It just occurred to me that I could take advantage of arithmetic
evaluation being performed when a variable with the -i integer
attribute is assigned a value to create a visual distinction between
working with regular variables and variables representing integers,
i.e.:

local this_var="words words words"
local var[index]="${this_var}"

local -r -i BIT_FLAG=2#0100
local -i value=BIT_FLAG

After doing this, var[index] will be set to "words words words" and
value will be set to 4.

Going a step further and passing integer arguments to functions as the
name of the variable, rather than passing its value with a parameter
expansion of that variable, we run into a problem. I would expect
func1 () and func2 () below to be equivalent. However, we see that
when setting a local variable with the integer attribute, using the
name of a variable at calling scope with the same name, the local
variable is always assigned the value 0, if I'm not using an
arithmetic expansion.

I wondered if the call to 'local' was already referencing the local
variable that it was in the process of declaring, which I imagine
would've been unset at the time. 'set -o nounset' didn't cause it to
error out, though.

Of course 'declare -i other=other' is a no-op, but it doesn't break.

Repeat-By:

$ cat integer-scope
#!/usr/bin/env bash

set -o nounset

main () {
  printf 'foo :\n'
  declare -i foo=1
  func1 foo
  func2 foo
  printf 'bar :\n'
  declare -i bar=2
  func1 bar
  func2 bar
  printf '"${baz}" :\n'
  declare -i baz=3
  func1 "${baz}"
  func2 "${baz}"
  printf 'other :\n'
  declare -i other=4
  declare -i other=other
  declare -p other
}

func1 () {
  declare -i bar="${1}"
  declare -p bar
}

func2 () {
  declare -i bar="$(( ${1} ))"
  declare -p bar
}

main

$ ./integer-scope
foo :
declare -i bar="1"
declare -i bar="1"
bar :
declare -i bar="0"
declare -i bar="2"
"${baz}" :
declare -i bar="3"
declare -i bar="3"
other :
declare -i other="4"