Re: [9front] Bug in rc

[Yury Chumak <sfynkx@gmail.com>]

Hitting limit is a half decision. In general, a strange decision is to
implement such non-limiting constructions using recursion. By the way,
in my real code there is a limit of 141 'case'-blocks, but there are
complex 'case' conditions in the blocks - apparently they are
additionally expanded.. So the test example is ideal at maximum, but
really the limit can be reached faster.

чт, 27 апр. 2023 г. в 03:46, <ori@eigenstate.org>:
>
> Quoth Yury Chumak <sfynkx@gmail.com>:
> > Hello all..
> >
> > Noticed that rc returns error 'stack overflow' if code consists
> > 'switch' construction with big amount of 'case' blocks. Steps to
> > reproduce:
> >
> > 1.Generate test script by next code:
> > #!/bin/rc
> > echo '#!/bin/rc' >test.rc
> > echo 'switch($*){' >>test.rc
> > for(i in `{seq 1 250}){
> >     echo ' case ' $i>>test.rc
> >     echo '    echo number ' $i>>test.rc
> > }
> > echo ' case *' >>test.rc
> > echo '    echo number none'>>test.rc
> > echo '}'>>test.rc
> >
> > 2. Run result script:
> > % chmod +x test.rc
> > % test.rc
> > ./test.rc:497: token 248: yacc stack overflow
> >
> > The 'switch' construction works normaly with number 'case' block less than 247.
> > In comparison linux's bash has no limitation to number elements in
> > 'case' block (at least 500k tested).
> >
>
> Yes, the grammar for this is right recursive,
> which means the full stack is collected before
> it's reduced:
>
>         body:   cmd
>         |       cmdsan body             {$$=tree2(';', $1, $2);}
>
> You can play around with refactoring it to be
> left recursive, or maybe bringing in the C rewrite
> of the parser from plan9port (ideally with tests).
>
> But I'm not sure why it matters; you can hit a
> limit with a huge switch, but it doesn't seem
> like a limit for practical code.
>


-- 
Sphynkx