Some minor $*-like expansion issues

[Grisha Levit]

A few silly (and admittedly unlikely to be encoutered) cases where the
behavior of certain expansions that should presumably mirror that of
$* differs.

With null IFS, leading/trailing spaces are removed from ${*:N} when
used for assignment:

    $ IFS=''
    $ set -- ' X '

    $ x=$* y=${*:1}; printf '<%s>\n' "$x" "$y"
    < X >
    <X>
    $ unset x y; printf '<%s>\n' ${x=$*} ${y=${*:1}}
    < X >
    <X>


With null IFS associative array keys are joined by space when used for
assignment:

    $ IFS=''
    $ set -- b a
    $ declare -A A=([b]= [a]=)

    $ x=$* y=${!A[*]}; printf '<%s>\n' "$x" "$y"
    <ba>
    <b a>
    $ unset x y; printf '<%s>\n' ${x=$*} ${y=${!A[*]}}
    <ba>
    <b a>

...and are expanded as a single field joined with spaces on the RHS of PE:

    $ unset x y; printf '<%s>\n' ${x-$*} ${y-${!A[*]}}
    <b>
    <a>
    <b a>


And a couple of issues with indirect expansion of * that have some
overlap with the above.

With:

    $ IFS=:
    $ set -- a b
    $ ind=*

Space is used to join fields instead of the first char of IFS here:

    $ x=$* y=${!ind}; printf '<%s>\n' "$x" "$y"
    <a:b>
    <a b>

And a single field joined with spaces is produced here:

    $ unset x y; printf '<%s>\n' ${x-$*} ${y-${!ind}}
    <a>
    <b>
    <a b>
    $ unset x y; printf '<%s>\n' ${x=$*} ${y=${!ind}}
    <a>
    <b>
    <a b>

Leading and trailing spaces are removed when the first character of
IFS is space or IFS is null or unset in this assignment case:

    $ set -- ' X '
    $ ind='*'

    $ IFS=$' \t\n'
    $ x=$* y=${!ind}; printf '<%s>\n' "$x" "$y"
    < X >
    <X>
    $ IFS=''
    $ x=$* y=${!ind}; printf '<%s>\n' "$x" "$y"
    < X >
    <X>


Perhaps related to some of the above, in the below cases, \001 and
\177 or combinations thereof are not properly treated, e.g.:

    $ IFS=''
    $ set -- $'\177'

    $ var=${*:1}; printf '<%q>\n' "$var"
    <''>
    $ unset var; printf '<%q>\n' ${var=${*:1}}
    <''>

Same for:

    declare -a a=($'\177')
    var=${a[*]:0}; printf '<%q>\n' "$var"
    unset var; printf '<%q>\n' ${var=${a[*]:0}}

    set -- $'\177'; ind='*'
    var=${!ind}; printf '<%q>\n' "$var"
    unset var; printf '<%q>\n' ${var=${!ind}}

Just for completeness, though this expansion is documented to be undefined:

    declare -A A=([0]=$'\177')
    var=${A[*]:0}; printf '<%q>\n' "$var"
    unset var; printf '<%q>\n' ${var=${A[*]:0}}