[augeas-devel] Improving the properties lens, issues with empty values

[Dominic Cleal]

Hi Carlos,

On 07/04/12 10:09, Carlos Sanchez wrote:
> I'm making a couple changes to the properties lens, but I'm struggling
> to get empty values working
> 
> I've made a fork on github [1] with the tests [2] that currently fail
> with something like
> 
> mykey=
> 
> A snippet of the lens:
> 
>   let sepch        = del /[ \t]*=[ \t]*/ "="
>   let value_to_eol = /[^ \t\n](.*[^ \t\n])?/
>   let entry        = /[A-Za-z][A-Za-z0-9._]+/
>   let property    = [ indent . key entry . sepch . store value_to_eol . eol ]
> 
> Any suggestions?
> may need to reorganize it and change more than just value_to_eol?

The first change I'd try would be to make the store value_to_eol
optional, giving you an entry without any value:

  let property    = [ indent . key entry . sepch . (store value_to_eol)? . eol ]

You'll find when you run augparse against the test that it'll fail
due to an ambiguity when there's no value_to_eol:

      'AA= \n' can be split into
      'AA=|=| \n'

     and
      'AA= |=|\n'

The single space can be consumed by either the sepch lens or the
eol.  To fix this, you can move the trailing space consumption
out of sepch and into the optional brackets created above:

  let sepch        = del /[ \t]*=/ "="
  let property    = [ indent . key entry . sepch . (indent . store value_to_eol)? . eol ]

This appears to work.  The unit test needs a small change for the
empty.property line.  An empty node would be stored with no value
rather than an empty string:

    { "empty.property" }

Let us know once you're happy with the changes and we'll merge
them.

Thanks,

-- 
Dominic Cleal
Red Hat Consulting
m: +44 (0)7817 878113