declare [-+]n behavior on existing (chained) namerefs

[Grisha Levit]

declare -n name=value, when name is already a nameref, shows the following presumably inconsistent behavior:

Given a chain of namerefs like:

ref_1 -> ref_2 -> ... -> ref_i ... -> ref_N [-> var]

• If ref_N points to a name that is not a nameref, the operations declare -n ref_N=value and declare +n ref_N modify the value/attributes of ref_N (this seems to be the desired behavior)
• For i<N, declare -n ref_i=value and declare +n ref_i modify the value/attributes of ref_N and not of ref_i
• If ref_N is declared as a nameref but unset, then these operations on ref_i have no effect.

For example, starting with:

unset -n ref{1..3}
declare -n ref1=ref2 ref2=ref3 ref3=var1

# declare -n ref1=var2
# declare -p ref{1..4}
declare -n ref1="ref2"   # unchanged
declare -n ref2="ref3"
declare -n ref3="var2"   # changed

# declare +n ref1
# declare -p ref{1..3}
declare -n ref1="ref2"   # unchanged
declare -n ref2="ref3"
declare -- ref3="var1"   # changed, no loner nameref

Or alternatively:

unset -n ref{1..3}
declare -n ref1=ref2 ref2=ref3 ref3

# declare +n ref1
# declare -p ref{1..3}
declare -n ref1="ref2"   # unchanged
declare -n ref2="ref3"   # unchanged
declare -n ref3          # unchanged

# declare -n ref1=var1
# declare -p ref{1..3}
declare -n ref1="ref2"
declare -n ref2="ref3"
declare -n ref3

The man page says:

All references, assignments, and attribute modifications to name, except for changing the -n attribute itself, are performed on the variable referenced by name’s value.

This does not appear to be the case, as declare -n ref_N=value changes $ref_N, not $value, and declare +n ref_i changes ref_N.

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