Re: Kconfig: '+config' valid syntax?

Paul Bolle
2015-07-02T12:10:18Z

[Spoiler: please start at the end of my reply.]

On do, 2015-07-02 at 13:57 +0200, Andreas Ruprecht wrote:
> On 07/02/2015 11:01, Paul Bolle wrote:
> > On Thu, 2015-07-02 at 10:08 +0200, Valentin Rothberg wrote:
> > Welcome to the wonders of lex and yacc!
> >
> > I try to spend as little time as possible looking at the lex rules,
> > so
> > I'm just guessing here. Anyhow, you might start by looking at this
> > snippet in zconf.l:
> > . {
> > unput(yytext[0]);
> > BEGIN(COMMAND);
> > }
> >
> >
> > <COMMAND>{
> > {n}+ {
> > [...]
> > }
> > .
> > \n {
> > BEGIN(INITIAL);
> > current_file->lineno++;
> > return T_EOL;
> > }
> > }
> >
> > Which perhaps translates to:
> > - ignore unknown stuff for now and go in COMMAND state;
> > - do something if we encounter some text ({n} = [A-Za-z0-9_]);
> > - go in INITIAL state if we encounter newlines or unknown stuff.
>
> This is _almost_ true (which I think is the problem). The rule for "."
> is empty, and not the same rule as for \n.

I see. That's nice to know.

> So what happens here, is that
> any unknown characters are simply ignored until something in {n}+
> shows up.

How can unknown characters be part of {n}+?

> If I add something like the following instead:
> + . {
> + fprintf(stderr, "something else: %s\n", yytext);
> + BEGIN(INITIAL);
> + }
>
> then Kconfig prints the message for the "+", but unfortunately also
> lots
> of "-" (which come from the occasional "---help---" instead of "help".
> As it looks to me, they are only ignored one step later inside the
> <PARAM> case.

(Years ago I submitted a few trivial cleanups for typos regarding "--
-help---". I should have followed up on those cleanups with a patch to
remove the silly lex rule that just ignores "---".

Perhaps we should add an actual definition for "---help---". On the
other hand: last time I checked nothing actually cares about the "---"
markers so adding them achieves nothing. Cleaning all Kconfig files to
get rid of these markers is probably not worth it. Add a checkpatch rule
to warn about their uselessness?)

> So changing it like the above is not the solution, but at least we
> know
> where the silent ignore is coming from...
>
> Any idea how to properly fix this?

As I said in my follow up: see commit 2e0d737fc76f ("kconfig: don't
silently ignore unhandled characters").

Thanks,

Paul Bolle