Here's an update, to be applied on top of the above patch. This
enables the k and v expansion flags to be used along side the P flag.

Attachment, Gist (http://gist.github.com/264465), and branch "pflag"
(git://github.com/Nomexous/zsh.git).

Michael Hwang

On Sat, Dec 26, 2009 at 7:59 PM, Michael Hwang
<michael.a.hwang@gmail.com> wrote:
> Sorry guys,
>
> Frank has just informed me that the patch didn't come through. So I'm
> reattaching it, providing a link (http://gist.github.com/264099), and
> providing a repo (git://github.com/Nomexous/zsh.git) where the changes
> can be retrieved from the "pflag" branch.
>
> Michael Hwang
>
> On Sat, Dec 26, 2009 at 5:48 PM, Michael Hwang
> <michael.a.hwang@gmail.com> wrote:
>> Hello all,
>>
>> In my opinion, the current behavior of the P expansion flag is not
>> intuitive, and possibly even buggy. For instance:
>>
>> % FOO='hello!'
>> % REF='FOO BAR'
>> % print ${(P)${REF}}
>> hello!
>>
>> In this case, ${(P)${REF}} should expand to nothing, because 'FOO BAR'
>> is not a proper parameter name. However, the current logic takes only
>> as much as makes sense, and ignores the rest. This creates confusion
>> with arrays:
>>
>> % ARRAY=(FOO CLUE SHOE)
>> % FOO=zsh
>> % CLUE=is
>> % SHOE=awesome
>> % print ${(P)${ARRAY}}
>> zsh
>>
>> One would think that each element of the reference ARRAY would
>> replaced by the value of the variable in that element. However, zsh
>> will just take the value of FOO, as it's the longest string that makes
>> sense as a variable name.
>>
>> On the more buggy-ish side:
>>
>> % STRING='zsh is awesome!'
>> % STR='zsh sucks... :-/'
>> % REF=STRING
>> % print ${(P)REF[1,3]}
>> zsh sucks... :-/
>>
>> As ${(P)REF} is really ${(P)${REF}}, one would think that that
>> ${(P)REF[1,3]} would be expanded as ${(P)${REF}[1,3]}. But as you can
>> see, it is instead expanded as ${(P)${REF[1,3]}}.
>>
>> This patch fixes all these problems. The concept of "subexpression" no
>> longer applies with the P flag. Instead, one should consider whether
>> or not the "inside" expression (I call it a "reference") expands to
>> more than one word.
>>
>> Notably:
>> 1.) A reference can now be a mix of plain text and expansions. For
>> example, ${(P)${FOO}_BAR}.
>> 2.) A reference can be quoted. Note that ${(P)"REF"} is now possible,
>> and expands as if it were ${(P)"${REF}"}.
>> 3.) If the reference expands to more than one word, then each element
>> will be expanded to take on the value of that variable. (See below.)
>>
>> It is simplest with quotes:
>>
>> % FOO='zsh.org'
>> % REF=FOO
>> % print ${(P)"REF"}
>> zsh.org
>> % print ${(P)"${REF}"}
>> zsh.org
>>
>> Fairly straight forward. But notice what happens when our reference
>> expands to a non-valid parameter name:
>>
>> % FOO='merry xmas!'
>> % REF='FOO FOO'
>> % print ${(P)"${REF}"}
>>
>> % print ${(P)"REF"}
>>
>>
>> Now try mixing (in quotes):
>>
>> % FOOBAR='buy champagne for new year'
>> % REF=FOO
>> % print ${(P)"${REF}BAR"}
>> buy champagne for new year
>>
>> The expansion takes on the value of the variable name that the insides
>> expand to.
>>
>> Without quotes, array references are possible.
>>
>> % REFS=(A B C)
>> % A=1
>> % B=2
>> % C=3
>> % print -l -- ${(P)${REFS}}
>> 1
>> 2
>> 3
>>
>> It is also possible to have an array reference with an element that
>> refers to an array parameter:
>>
>> % REFS=(A B C)
>> % A=1
>> % B=(2 two)
>> % C=3
>> % print -l -- ${(P)${REFS}}
>> 1
>> 2
>> two
>> 3
>>
>> And finally, mixing, non-quoted.
>>
>> % REFS=(FOO CLUE SHOE)
>> % FOOBAR=zsh
>> % CLUEBAR=is
>> % SHOEBAR=awesome
>> % print ${(P)${^REFS}BAR}
>> zsh is awesome
>>
>> Note that ${(P)${REFS}BAR} would just expand to "awesome", as
>> ${REFS}BAR expands to the words "FOO" "CLUE" "SHOEBAR", with FOO and
>> CLUE not being set.
>>
>> Please test these changes. paramsubst() took a long time to
>> understand, so I'm sure that I've introduced a bug or two.
>>
>> Michael Hwang
>>
>