Issue #14654 has been reported by Reid Vandewiele.
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Feature #14654: :undef should not be synonymous with the empty string in Puppet
if/case/selector
https://projects.puppetlabs.com/issues/14654
Author: Reid Vandewiele
Status: Unreviewed
Priority: Normal
Assignee:
Category:
Target version: Waldorf
Affected Puppet version:
Keywords:
Branch:
This feature request is a spin-off of the resolution of #8778.
In trying to trace back through :undef-related tickets in order to get a better
idea of what the intention moving forward is, I unearthed issues #4692, #6621,
#6745, #8783, and #13210. Most of those tickets were about exposing the :undef
symbol in ruby (custom functions, templates) but in a completely biased fashion
I came up with a few quotes that I think are more generally applicable to the
use of 'undef' in the Puppet DSL.
Paul Berry in #4692:
> We’d intended for :undef to only be used internally within Puppet to
> distinguish between undefined variables and variables whose values are the
> empty string.
Matt Robinson in #8783:
> Puppet’s concept of undef seems fairly easy to confuse with empty string,
> Ruby’s nil, and often gets exposed through the symbol :undef when it
> shouldn’t. It doesn’t seem to me like there’s an overall philosophy behind
> undef and how it should be treated in Puppet.
Chris Price in #13210:
> [...] there are cases in the world where there is a meaningful semantic
> distinction between “null” and an empty string (plenty of precedent for this
> in relational databases, etc.), and [...] our current implementation
> explicitly prevents users from handling that distinction.
It's because of the latter-most sentiment that code I am familiar with
deliberately checks to see if values are undef rather than empty strings (`if
$val == undef`), and expects there to be a difference. These checks all break
starting with Puppet 2.7.15 as a result of the #8778 resolution.
The style guide currently recommends against checking to see if a value is
undef, suggesting instead that a picked-from-a-hat 'UNSET' string should be
used in class parameter defaults and that DSL code should be written to handle
that conventionally defined string rather than using a language-level "null"
check. The fact that this used to work (with :undef) was a bug.
Fixing the #8778 bug resulted in Puppet more consistently enforcing the
inconsistency of :undef in the Puppet DSL. Consider the following example which
for 2.7.15rc1 or greater demonstrates a situation in which :undef is already
not synonymous with the empty string.
notify { "if message is undef, the title will be used instead":
message => undef,
}
if "" == undef {
notify { "then this message should not be empty":
message => "",
}
}
## Feature Request ##
In order to allow users to account for the meaningful distinction between
"null" and an empty string, :undef should not be synonymous with the empty
string in Puppet if/case/selector. For if/case/selector checks, it should be
that undef == undef, but nothing else. undef != '' and '' != undef.
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