Re: BUG: zsh-3.1.5-pws-14: parameter expansion not working properly

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxx>]

On Apr 15,  2:08pm, Sven Wischnowsky wrote:
} Subject: Re: BUG: zsh-3.1.5-pws-14: parameter expansion not working proper
}
} We have this call chain:
} 
}    A paramsubst(), calls
}    B    multsub(), calls
}    C       paramsubst()
} 
} Now, we could make the multsub() save (and at the end restore) the
} value of, say `static int mult_isarr'. It then sets it to zero and
} calls paramsubst() (via prefork(), as usual). At the end of
} paramsubst() we set `mult_isarr = isarr'.

I actually tried this last night -- although I had paramsubst() set the
static to 0 on the way in; multsub() just saved and restored it -- and
it worked for some cases but not others, so I decided I was missing a
subtlety somewhere and threw it out.

} After the prefork(), multsub() now knows that the list it gets was an
} array expression if `mult_isarr != 0'.

Right; this is interesting only when there's exactly one linknode in the
list returned by prefork().  (Hmm, or is it also interesting for zero
linknodes?  Should an empty array behave the same as an unset parameter,
or not?  Ah, no, it should not -- "$@" goes away entirely when $# == 0,
but "$*" yields the empty string.)

} This was the first part of what I meant -- getting information about
} the array'ness. With the other part I meant the call to multsub() we
} are talking about here (line 980). There we have to decide if we give
} `&aval' or `NULL' to multsub() where it is used to decide if the
} joining should be done -- the problem to solve, as you said.

Actually, that's NOT the problem to solve, or at least I didn't think so.
I think the code was correct back when `aspar' was the sole determinant
of whether NULL was passed in.  It's `mult_isarr', as you call it, that
should otherwise determine whether multsub() does a join.

} > No, that's too confusing and not necessary.  The only real issue is the
} > "precedence" if you will, of subscripting vs. joining.

The foregoing is the important point; I was confused here:

} > We "solved" the problem of subscripting scalars that were
} > accidentally treated as arrays, by forcing all quoted arrays to
} > be taken as scalars; I think we need to back off from that and
} > concentrate on not accidentally treating scalars as arrays.
} 
} I don't think I understand this. And I thought I kept it from arrays
} being accidentally being treated as scalars.

Um, yes; that's probably the subtlety that I missed.

} From your first mail about this I got the impression that you wanted
} nested expressions to keep their knowledge about whether they are
} arrays or not, so that (with foo being an array) in "${${${${(@)foo}}}[1]}"
} the outer paramsubst() (A) gets notified by multsub() (B) that the
} inner paramsubst() (C) returned an array and the subscripting gives
} the first array element.

Yes, that's the general idea.  I'm not sure how many levels of ${ } the
array-ness should propagate through, except that I currently believe it
should be at least one more level than it currently does.

Think about it this way:

1. The expression "${(@)foo}" produces an array of quoted words.

2. In the expression "${${(@)foo}}", the outer ${ ... } can include both
flags in leading () and subscripts in trailing [].  The inner ${(@)foo}
should *still* produce an array of quoted words, to which the flags and
subscripts of the outer ${ ... } are applied.

3. To work like the old zsh, the subscripts should apply *before* any
split or join operation implied by the flags (or by the lack of a flag).
The exception being the (P) flag, because it is defined to change the
interpretation of the parameter's name and thus must "bind tighter" than
anything including subscripts.

In pws-14+, at step (2), the inner expression does NOT produce an array
unless the outer expression uses (@).  This is what I think is wrong.
I don't think it's possible to "pass down" from paramsubst-->multsub
the knowledge of whether an array should be returned [except when (P)];
it has to be "passed up," multsub<--prefork<--stringsubst<--paramsubst.

Beyond those three steps, things get fuzzy.  In trying to reason about
this without actually seeing it in action, I *believe* that it's OK if:

4. *After* the subscripts are applied, the outer ${ ... } joins the
quoted words into a single string, *unless*: the (@) flag is present
or the [@] subscript was applied, and the (j) flag is not present.

I know that's still a change from the old behavior, so I can't be sure
that it'll work out, but I *think* it will.

5. Finally, the string is split again according to SHWORDSPLIT or the
(s) flag.

6. If there is a split, or if (@) or [@] was present, an array of quoted
words is returned.  If there's another outer ${ ... }, go to step (3).

} With respect to the outer paramsubst()s this would make things
} independent of whether the whole thing is in quotes or not, only the
} inner paramsubst()s `control' if the outer ones work on an array
} by testing if the thing is in quotes and if the `(@)' flag (or
} something similar like the `s' flag or `=') is used.

As I just said, I don't *think* it should be independent of whether the
whole thing is in quotes.  The quotes should affect what happens at (4),
but they should *not* affect what happens at 2-->3 or 6-->3.

Does that make sense?

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com