[perl #127279] [BUG] Infinite loop with |"a".."z"

[Brian S. Julin via RT]

On Fri, 06 Oct 2017 19:32:17 -0700, b...@abrij.org wrote:
> On Fri, 15 Jan 2016 10:24:16 -0800, c...@zoffix.com wrote:
> > The slip (|) before a range has higher precedence and it interprets
> > the starting point of the range as a single-item list. This leads to
> > two types of bugs, and both situations should likely be error
> > messages:
> >
> > 1) Infinite loop when range contains letters, as the range starts
> > from
> > 1 and tries to reach the second letter by increasing a number:
> >
> > <ZoffixW> m: .say for |"g".."z";
> > <camelia> rakudo-moar 3259ba:
> > OUTPUT«(timeout)1␤2␤3␤4␤5␤6␤7␤8␤9␤10␤11␤12␤13␤14␤15␤16␤17␤18␤19␤20␤21␤22␤23␤24␤25␤26␤27␤28␤29␤30␤31␤32␤33␤34␤35␤36␤37␤38␤39␤40␤41␤42␤43␤44␤45␤46␤47␤48␤49␤50␤51␤5…»
> >
> > 2) Incorrect range is produced when numbers are used for the range.
> > It'll always start at 1 and proceed until the end number:
> > <ZoffixW> m: .say for |10..20
> > <camelia> rakudo-moar 3259ba:
> > OUTPUT«1␤2␤3␤4␤5␤6␤7␤8␤9␤10␤11␤12␤13␤14␤15␤16␤17␤18␤19␤20␤»
> > <ZoffixW> m: .say for |10..5
> > <camelia> rakudo-moar 3259ba: OUTPUT«1␤2␤3␤4␤5␤»
> >
> > Relevant IRC conversation: http://irclog.perlgeek.de/perl6/2016-01-
> > 15#i_11894289
> 
> I submitted:
> 
> https://github.com/rakudo/rakudo/pull/1182
> 
> ...which warns on these:
> 
> $ perl6 -e 'say |4..5'
> Potential difficulties:
>     To apply a Slip flattener to a range, parenthesize the whole
> range.
>     (Or parenthesize the whole endpoint expression, if you meant
> that.)
>     at -e:1
>     ------> say ⏏|4..5
> 1..5
> $ perl6 -e 'say ~4..5'
> Potential difficulties:
>     To stringify a range, parenthesize the whole range.
>     (Or parenthesize the whole endpoint expression, if you meant
> that.)
>     at -e:1
>     ------> say ⏏~4..5
> "4"..5
> $ perl6 -e 'say |4 R.. 5'
> Potential difficulties:
>     To apply a Slip flattener to a range, parenthesize the whole
> range.
>     (Or parenthesize the whole endpoint expression, if you meant
> that.)
>     at -e:1
>     ------> say ⏏|4 R.. 5
> 5..1
> $ perl6 -e 'say ~4 R.. 5'
> Potential difficulties:
>     To stringify a range, parenthesize the whole range.
>     (Or parenthesize the whole endpoint expression, if you meant
> that.)
>     at -e:1
>     ------> say ⏏~4 R.. 5
> 5..4
> 
> (don't know why that last one "works", but still worth warning.)
> 
> It also handles all the ^..^ variants.


OK, PR merged in rakudo cb9d2e040

Tests in roast 6e9bab5de

These are just worries, not errors, but good enough?