"no warnings 'exec'" does not disable "Statement unlikely to be reached"

[p5pRT]

Migrated from rt.perl.org#118455 (status was 'resolved')

Searchable as RT118455$

[p5pRT]

From @rjbs

Created by @rjbs

I don't have a program called "lll" in my path.

  ~$ perl -Mwarnings -E 'exec "lll"; say "oops"'
  Statement unlikely to be reached at -e line 1.
  (Maybe you meant system() when you said exec()?)
  Can't exec "lll"​: No such file or directory at -e line 1.
  oops

I get two warnings, both "exec" category, as expected.

I don't want these. I will disable that category.

  perl -Mwarnings -E 'no warnings "exec"; exec "lll"; say "oops"'
  Statement unlikely to be reached at -e line 1.
  (Maybe you meant system() when you said exec()?)
  oops

I only managed to disable one of them!

The docs in perldiag make it clear how to disable this warning, and that
works. Fine. But why can't it also be disabled like any other lexical
warning?

More​:

With only unrelated warnings turned on, no warning. Great.

  ~$ perl -E 'use warnings "exiting"; exec "lll"; say "oops"'
  oops

Turning on the "exec" category does not *enable* the warning​:

  ~$ perl -E 'use warnings "exec"; exec "lll"; say "oops"'
  Can't exec "lll"​: No such file or directory at -e line 1.
  oops

Turning off all warnings *does* disable the warning​:

  ~$ perl -E 'use warnings; no warnings; exec "lll"; say "oops"'
  oops

Looking at the difference between the two warnings (in op.c and doio.c)
didn't make it obviously clear to me what differs.

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl 5.19.0:

Configured by rjbs at Mon May 20 10:59:20 EDT 2013.

Summary of my perl5 (revision 5 version 19 subversion 0) configuration:
   
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Locally applied patches:
    


@INC for perl 5.19.0:
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    /Users/rjbs/.perlbrew/libs/19.0@std/lib/perl5
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    /Users/rjbs/perl5/perlbrew/perls/19.0/lib/site_perl/5.19.0
    /Users/rjbs/perl5/perlbrew/perls/19.0/lib/5.19.0/darwin-2level
    /Users/rjbs/perl5/perlbrew/perls/19.0/lib/5.19.0
    .


Environment for perl 5.19.0:
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[p5pRT]

From @rjbs

I have pushed 3cf2ee4e44b339198562fa5f52af6a52e85d52a8 as smoke-me/rjbs/exec-
warning.

Please give it a look, anybody, and comment before I merge in a day or three.

--
rjbs

[p5pRT]

@rjbs - Status changed from 'new' to 'open'

[p5pRT]

From @cpansprout

On Wed Jun 12 12​:53​:10 2013, rjbs wrote​:

I have pushed 3cf2ee4e44b339198562fa5f52af6a52e85d52a8 as smoke-
me/rjbs/exec-
warning.

Please give it a look, anybody, and comment before I merge in a day or
three.

The fix looks perfectly correct to me.

Interestingly....

599cee7 (Aug 98) put it in the syntax category. eeb6a2c (Jan
2000, entitled ‘wrong category for exec() warning’) made it inconsistent.

So ‘use warnings "syntax"’ enables that warning. ‘use warnings FATAL =>
'exec'’ fatalizes it; but, of course, it is only fatal if it happens,
which is when ‘syntax’ warnings are enabled. Fascinating. :-)

--

Father Chrysostomos

[p5pRT]

From @rjbs

* Father Chrysostomos via RT <perlbug-followup@​perl.org> [2013-06-12T21​:08​:04]

So ‘use warnings "syntax"’ enables that warning. ‘use warnings FATAL =>
'exec'’ fatalizes it; but, of course, it is only fatal if it happens,
which is when ‘syntax’ warnings are enabled. Fascinating. :-)

Yeah, once the ckWARN was pointed out, this behavior became clear, and I stared
slack-jawed at my oneliners for a while.

I will merge this fix tonight or tomorrow.

--
rjbs

[p5pRT]

From @cpansprout

On Thu Jun 13 06​:14​:07 2013, perl.p5p@​rjbs.manxome.org wrote​:

I will merge this fix tonight or tomorrow.

as 573d2b1.

--

Father Chrysostomos

[p5pRT]

@cpansprout - Status changed from 'open' to 'resolved'