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Smartmatch against m// operator mishandles junctions #6455

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p6rt opened this issue Aug 18, 2017 · 7 comments
Open

Smartmatch against m// operator mishandles junctions #6455

p6rt opened this issue Aug 18, 2017 · 7 comments
Labels
Bug regex Regular expressions, pattern matching, user-defined grammars, tokens and rules

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@p6rt
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p6rt commented Aug 18, 2017

Migrated from rt.perl.org#131925 (status was 'open')

Searchable as RT131925$

@p6rt
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p6rt commented Aug 18, 2017

From @AlexDaniel

Code​:
say so $*DISTRO.Str|$*KERNEL.Str ~~ /linux/

Result​:
True

Code​:
say so $*DISTRO.Str|$*KERNEL.Str ~~ m/linux/

Result​:
False

I'd expect the result to be identical in both cases.

IRC log​: https://irclog.perlgeek.de/perl6-dev/2017-08-18#i_15039736

@p6rt
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p6rt commented Aug 19, 2017

From @smls

The problem only appears if `m//` is used directly as the RHS of `~~`​:

  $_ = 'a' | 'b';
  say m/a/; # any(ï½¢aï½£, Nil)
  say $_ ~~ m/a/; # False
  say $_ ~~ { m/a/ }; # any(ï½¢aï½£, Nil)

@p6rt
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p6rt commented Aug 19, 2017

The RT System itself - Status changed from 'new' to 'open'

@p6rt
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p6rt commented Aug 19, 2017

From @smls

<smls> bisectable6​: say <a b>.any ~~ m/a/;
<bisectable6> smls, On both starting points (old=2015.12 new=e3e29c5)
  the exit code is 0 and the output is identical as well
<bisectable6> smls, Output on both points​: «False»

@p6rt
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p6rt commented Oct 15, 2017

From @zoffixznet

On Fri, 18 Aug 2017 13​:26​:25 -0700, alex.jakimenko@​gmail.com wrote​:

Code​:
say so $*DISTRO.Str|$*KERNEL.Str ~~ /linux/

Result​:
True

Code​:
say so $*DISTRO.Str|$*KERNEL.Str ~~ m/linux/

Result​:
False

I'd expect the result to be identical in both cases.

IRC log​: https://irclog.perlgeek.de/perl6-dev/2017-08-18#i_15039736

This now[^1] returns True for both cases, so don't understand why and
unsure whether the bug is actually fixed or if that commit just shadowed it.

[1] rakudo/rakudo@8a0f6ac

@p6rt p6rt added Bug regex Regular expressions, pattern matching, user-defined grammars, tokens and rules labels Jan 5, 2020
@jubilatious1
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jubilatious1 commented Mar 30, 2020

I thought this was related to (but maybe not):

Match operator: error with any() junction and user-defined $_ topic variable
rakudo/rakudo#3221

mbook:~ homedir$ perl6
To exit type 'exit' or '^D'
> say so ("dog" | "cat")  ~~ m/dog/;
True
> say $/; say $_;
any(「dog」, (Any))
(Any)
> say so ("dog" | "cat")  ~~ m/cat/;
True
> say $/; say $_;
any((Any), 「cat」)
(Any)
> say so ("dog" | "cat")  ~~ m/linux/;
True
> say $/; say $_;
any((Any), (Any))
(Any)
> say $*VM
moar (2020.02.1)
> exit
mbook:~ homedir$ perl6

@raiph
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raiph commented Mar 20, 2021

It's not so much "Smartmatch against m// operator mishandles junctions" as it is that the user is expecting it to do what they mean.

I've documented the behaviour (though with the strings being 'a'|'b') in rakudo/rakudo#4002 (comment):

The False is correct. The ~~ sets $_ to any('a','b'). Then it evaluates m/./. The result is any(「a」, 「b」), and $/ set to the same value. Then the ~~ calls .ACCEPTS on that value, i.e. it does the same as any('a','b') ~~ any(「a」, 「b」). That evaluates to False.

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Labels
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