Re: Feature Request: Allow skipping zsh statement on return from trap DEBUG

[Stephane Chazelas <stephane.chazelas@xxxxxxxxx>]

2019-10-24 16:17:27 -0400, Rocky Bernstein:
> A while ago I wrote a debugger for zsh called zshdb
> <https://zshdb.readthedocs.io/en/latest/>. See also
> https://repology.org/project/zshdb/versions .
> 
> A feature that is missing in the debugger and that is available in the
> corresponding debugger for bash, bashdb,  is the skip command.
> 
> This command skips over the upcoming statement to be executed. The way this
> works in bashdb, is that if the debug hook returns with a nonzero value.
> The way BASH works is that if the trap DEBUG hook returns a nonzero value,
> BASH skips statement to be run.
> 
> Thoughts about extening zsh so that it too will skip the upcoming statement
> if the zsh trap DEBUG hook return a non-zero value.  Or more generally some
> means by which a DEBUG hook can indicate to zsh to skip the upcoming
> statement?
[...]

See info zsh trap:

}  If SIG is DEBUG then ARG will be executed before each command if
}  the option DEBUG_BEFORE_CMD is set (as it is by default), else
}  after each command.  Here, a 'command' is what is described as a
}  'sublist' in the shell grammar, see *note Simple Commands &
}  Pipelines::.  If DEBUG_BEFORE_CMD is set various additional
}  features are available.  First, it is possible to skip the next
}  command by setting the option ERR_EXIT; see the description of the
}  ERR_EXIT option in *note Description of Options::.  Also, the shell
}  parameter ZSH_DEBUG_CMD is set to the string corresponding to the
}  command to be executed following the trap.  Note that this string
}  is reconstructed from the internal format and may not be formatted
}  the same way as the original text.  The parameter is unset after
}  the trap is executed.

Was added in 2008: https://www.zsh.org/mla/workers/2008/msg01075.html

You participated in that discussion, sounds likely you actually
requested the feature then.

TRAPDEBUG() {
  echo "$ZSH_DEBUG_CMD"
  [[ $ZSH_DEBUG_CMD = *x* ]] && set -o errexit
}
echo x
echo y


gives:

echo x
echo y
y

-- 
Stephane