Puppet users - Apr 2011 - ERB strangness, or ruby/puppet internals I don't understand

Let''s say I have a very simple template
template.erb:
<% if not has_variable?("foobar") then foobar =
"undefined" end -%>
foobar: <%= foobar %>
class: <%= foobar.class %>

And a basic manifest:
template.pp:
$mytemp = template(''template.erb'')
notice($mytemp)

And then I apply the manifest, with an undefined foobar (no foobar fact):
$ puppet apply ~/template.pp
notice: Scope(Class[main]): foobar: undefined
class: String

notice: Finished catalog run in 0.01 seconds

Looking good. So now I apply the manifest, but with a defined value
for foobar (via the FACTER_FOOBAR environment variable):
$ FACTER_FOOBAR=''foo'' puppet apply ~/template.pp
notice: Scope(Class[main]): foobar:
class: NilClass

notice: Finished catalog run in 0.01 seconds

Er, what? How on earth did foobar go from a String to NilClass? I
can''t fathom how this is expected, or correct...

The reason I was doing this sort of thing is to give a possibly
missing fact a default value. I ended up using a second variable, like
this:
<% foo = has_variable?("foobar") ? foobar.to_s : "false"
-%>

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On 04/15/2011 09:10 PM, Clay Caviness wrote:
> Let''s say I have a very simple template
> template.erb:
> <% if not has_variable?("foobar") then foobar =
"undefined" end -%>
> foobar: <%= foobar %>
> class: <%= foobar.class %>
> 
> And a basic manifest:
> template.pp:
> $mytemp = template(''template.erb'')
> notice($mytemp)
> 
> And then I apply the manifest, with an undefined foobar (no foobar fact):
> $ puppet apply ~/template.pp
> notice: Scope(Class[main]): foobar: undefined
> class: String
> 
> notice: Finished catalog run in 0.01 seconds
> 
> Looking good. So now I apply the manifest, but with a defined value
> for foobar (via the FACTER_FOOBAR environment variable):
> $ FACTER_FOOBAR=''foo'' puppet apply ~/template.pp
> notice: Scope(Class[main]): foobar:
> class: NilClass
> 
> notice: Finished catalog run in 0.01 seconds
> 
> Er, what? How on earth did foobar go from a String to NilClass? I
> can''t fathom how this is expected, or correct...
> 
> The reason I was doing this sort of thing is to give a possibly
> missing fact a default value. I ended up using a second variable, like
> this:
> <% foo = has_variable?("foobar") ? foobar.to_s :
"false" -%>
> 
Hi,

does this work better if you set $foobar in your manifest?

Looks like a bug you may want to report either way.

Regards,
Felix

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On Apr 15, 2:10 pm, Clay Caviness <ccavin...@gmail.com>
wrote:
> Let''s say I have a very simple template
> template.erb:
> <% if not has_variable?("foobar") then foobar =
"undefined" end -%>
> foobar: <%= foobar %>
> class: <%= foobar.class %>
>
> And a basic manifest:
> template.pp:
> $mytemp = template(''template.erb'')
> notice($mytemp)
>
> And then I apply the manifest, with an undefined foobar (no foobar fact):
> $ puppet apply ~/template.pp
> notice: Scope(Class[main]): foobar: undefined
> class: String
>
> notice: Finished catalog run in 0.01 seconds
>
> Looking good. So now I apply the manifest, but with a defined value
> for foobar (via the FACTER_FOOBAR environment variable):
> $ FACTER_FOOBAR=''foo'' puppet apply ~/template.pp
> notice: Scope(Class[main]): foobar:
> class: NilClass
>
> notice: Finished catalog run in 0.01 seconds
>
> Er, what? How on earth did foobar go from a String to NilClass? I
> can''t fathom how this is expected, or correct...
It looks like the variable is defined, and has the (Ruby) value nil.
This could be because the variable was previously assigned a (possibly
different) value when a different catalog was compiled, but not
assigned a value for the current catalog.  And THAT might be because
Ruby and shell variable names are both case-sensitive.  Does it work
better if you write

    FACTER_foobar=''foo'' puppet apply ~/template.pp

?
>
> The reason I was doing this sort of thing is to give a possibly
> missing fact a default value. I ended up using a second variable, like
> this:
> <% foo = has_variable?("foobar") ? foobar.to_s :
"false" -%>

If I have analyzed the problem correctly, then you should also be able
to do it this way:

<% if not has_variable?("foobar") or foobar.nil then foobar
"undefined" end -%>


John

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On 2011-04-15 21:10, Clay Caviness wrote:
> Let''s say I have a very simple template
> template.erb:
> <% if not has_variable?("foobar") then foobar =
"undefined" end -%>
> foobar: <%= foobar %>
> class: <%= foobar.class %>
> 
> And a basic manifest:
> template.pp:
> $mytemp = template(''template.erb'')
> notice($mytemp)
> 
> And then I apply the manifest, with an undefined foobar (no foobar fact):
> $ puppet apply ~/template.pp
> notice: Scope(Class[main]): foobar: undefined
> class: String
> 
> notice: Finished catalog run in 0.01 seconds
> 
> Looking good. So now I apply the manifest, but with a defined value
> for foobar (via the FACTER_FOOBAR environment variable):
> $ FACTER_FOOBAR=''foo'' puppet apply ~/template.pp
> notice: Scope(Class[main]): foobar:
> class: NilClass
> 
> notice: Finished catalog run in 0.01 seconds
> 
> Er, what? How on earth did foobar go from a String to NilClass? I
> can''t fathom how this is expected, or correct...
This happens because the Puppet variables are not exposed to ERB
as real Ruby variables.  Instead, Puppet uses some magic to catch
references to non-existing variables.  When the Ruby compiler sees
that you are assigning to foobar in your code, *anywhere* in your
code, it will create that variable for you, regardless of whether
the assignment is actually executed or not.  Since the variable now
exists, that will shadow Puppet''s magic.

That was at least what I found out when I investigated this when
running 0.24.something, and I don''t *think* they have changed how
Puppet variables are exposed to ERB since then.

> The reason I was doing this sort of thing is to give a possibly
> missing fact a default value. I ended up using a second variable, like
> this:
> <% foo = has_variable?("foobar") ? foobar.to_s :
"false" -%>
That is probably the best workaround.


	/Bellman

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