Re: while alias

[Pier Paolo Grassi <pierpaolog@gmail.com>]

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thanks the space before the brace indeed solved it. good to know!

Pier Paolo Grassi


Il giorno mar 8 nov 2022 alle ore 13:40 Peter Stephenson <
p.w.stephenson@ntlworld.com> ha scritto:

> (This is really for zsh-workers but in case anyone wants to see the
> result...)
>
> > On 08/11/2022 06:13 Bart Schaefer <schaefer@brasslantern.com> wrote:
> > On Mon, Nov 7, 2022 at 5:57 PM Pier Paolo Grassi <pierpaolog@gmail.com>
> wrote:
> > >
> > > Hello, I have the following alias defined:
> > >
> > > WI='while {read -r it; ! [[ $? -ne 0 && -z $it ]]}'
> > >
> > > that works fine except in command substitution:
> >
> > Put spaces around your braces.
> >
> > alias WI='while { read -r it; ! [[ $? -ne 0 && -z $it ]] }'
> >
> > Aliases in command substitutions are parsed by a complicated dance
> > requiring that they be expanded and then backtracked over and then
> > re-parsed.  The character count for the "{" and/or "}" tokens is off
> > by one for the backtracking step when they don't have surrounding
> > whitespace.  (Leaving it to PWS, who choreographed this dance number,
> > to fix the footwork if possible.)
>
> Yes, it's that full combination of a command substitution, an
> alias, and expansion text with a lexically significant closing brace
> with no preceding space that's doing it, so it's very specific.
>
> This will come as a shock, but there's a hack in the lexical analyser!
> (Counselling will be available by the usual channels.)  It seems
> that the lexer really doesn't like closing braces without a space
> before them and sometimes we have to fix up the text after the event.
>
> It seems the extra special code for command substitution needs a
> slightly modified version of the hack.  The new test in D08 checks
> the case Pier Paolo hit; it turns out the existing test just above
> checks the case where we do after all need to unget an extra closing
> brace, i.e. lex_add_raw ends up 1 in the code added by the first hunk.
>
> I am not going to attempt to get my mind round this any further
> and will be going out for some fresh air.
>
> pws
>
> diff --git a/Src/lex.c b/Src/lex.c
> index ece02659e..e2f8bcfb1 100644
> --- a/Src/lex.c
> +++ b/Src/lex.c
> @@ -1429,10 +1429,18 @@ gettokstr(int c, int sub)
>                peek == STRING && lexbuf.ptr[-1] == '}' &&
>                lexbuf.ptr[-2] != Bnull) {
>         /* hack to get {foo} command syntax work */
> +       /*
> +        * Alias expansion when parsing command substitution means that
> +        * the case for raw lexical analysis may not be the same.
> +        * (Just go with it, OK?)
> +        */
> +       int lar = lex_add_raw;
> +       lex_add_raw = lexbuf_raw.len > 0 && lexbuf_raw.ptr[-1] == '}';
>         lexbuf.ptr--;
>         lexbuf.len--;
>         lexstop = 0;
>         hungetc('}');
> +       lex_add_raw = lar;
>      }
>      *lexbuf.ptr = '\0';
>      DPUTS(cmdsp != ocmdsp, "BUG: gettok: cmdstack changed.");
> diff --git a/Test/D08cmdsubst.ztst b/Test/D08cmdsubst.ztst
> index 04bf698aa..8b6bcb469 100644
> --- a/Test/D08cmdsubst.ztst
> +++ b/Test/D08cmdsubst.ztst
> @@ -177,3 +177,11 @@
>  0:Alias expansion needed in parsing substitutions
>  >hi
>  >bye
> +
> +# This should silently print a blank line; the original problem was
> +# a parse error as the last character of the unexpanded alias
> +# was erased, symptom: "command not found: W"
> +  alias WI='while {false}'
> +  eval 'echo $(WI blah)'
> +0:Aliases with braces in command substitution can cause havoc
> +>
>
>

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