[netmod] Questions about namings and prefixes in leafrefs

[Paul Borman <[e-mail]>]

Hi, I am trying to understand RFC6020 without having had the benefit of
being in any of the discussions of the working group.  I have found the
discussion of path names unclear so I have used pyang to try and understand
what is expected.  It seems to me that a path in a leafref:

   - may descend into submodule's containers
   - may descend into used groupings, no matter where the grouping is
   defined
   - may *not* ascend into the parent module
   - may optionally use the module's prefix for any element in a leafref
   path, no matter where the element is defined
   - may optionally use the belongs-to-prefix in elements in paths inside a
   submodule
   - may *never* use the prefix for/from an imported module

Some questions this raise are:

   - are these observations correct (and intended)?
   - is there ever a time where a prefix is required in a leafref path?

Attached are the modules and submodules I used that lead to these
assumptions and questions.  pyang -f tree produces the following errors:

base.yang:50: error: other:other-group-container-leaf1 in the path for
base-container-badref1 at base.yang:49 is not found
base.yang:53: error: prefix "pother" is not defined (reported only once)
sub.yang:15: error: base:base-container in the path for sub-badref2 at
sub.yang:14 is not found
sub.yang:18: error: base:base-container in the path for sub-badref3 at
sub.yang:17 is not found

I am also trying to understand the prefixes used in XPath representations.
I have tried using --tree-prefix but that does not appear to accept any
prefixes.

Thanks for any guidance,

    -Paul

// Base test yang module.
module base {
  namespace "urn:mod";
  prefix "base";

  include sub;
  import other {
    prefix bother;
  }

  grouping base-group {
    leaf base-group-leaf { type string; }
  }

  // test uses and leaf ref
  container base-container {
    uses base-group;
    uses bother:other-group;
    uses base:sub-group;
    leaf base-container-leaf { type string; }
    leaf base-container-ref1 {
      type leafref { path ../base-container-leaf; }
    }
    leaf base-container-ref2 {
      type leafref { path ../base-group-leaf; }
    }
    leaf base-container-ref3 {
      type leafref { path ../other-group-leaf; }
    }
    leaf base-container-ref4 {
      type leafref { path ../sub-group-container/sub-group-leaf; }
    }
    leaf base-container-ref5 {
      type leafref { path ../../base:sub-container/sub-container-leaf; }
    }
    leaf base-container-ref6 {
      type leafref { path ../../base:sub-container/base:sub-container-leaf;
}
    }
    leaf base-container-ref7 {
      type leafref { path ../../sub-container/base:sub-container-leaf; }
    }
    leaf base-container-ref8 {
      type leafref { path
../other-group-container/other-group-container-leaf1; }
    }
    leaf base-container-ref9 {
      type leafref { path
../other-group-container/base:other-group-container-leaf1; }
    }
    // These next two ar invalid
    leaf base-container-badref1 {
      type leafref { path
../other-group-container/bother:other-group-container-leaf1; }
    }
    leaf base-container-badref2 {
      type leafref { path
../other-group-container/pother:other-group-container-leaf1; }
    }
  }
}

// included by base.yang.
submodule sub {
  belongs-to base { prefix "sbase"; }
  container sub-container {
    leaf sub-container-leaf { type string; }
    container subsub {
      leaf sub-leafref {
        type leafref { path ../../sub-container-leaf; }
      }
      leaf sub-leafref1 {
        type leafref { path ../../sbase:sub-container-leaf; }
      }
      // the next two both fail trying to ascend into the parent
      leaf sub-badref2 {
        type leafref { path ../../../base-container/base-container-leaf; }
      }
      leaf sub-badref3 {
        type leafref { path
../../../sbase:base-container/base-container-leaf; }
      }
    }
  }
  grouping sub-group {
    container sub-group-container {
      leaf sub-group-leaf { type string; }
    }
  }
}

// imported by base.yang.
module other {
  namespace "uri:empty";
  prefix "otherp";
  container other-container {
    leaf other-container-leaf1 { type string; }
    leaf other-container-leaf2 { type string; }
  }
  grouping other-group {
    leaf other-group-leaf { type string; }
    container  other-group-container {
      leaf other-group-container-leaf1 { type string; }
      leaf other-group-container-leaf2 { type string; }
    }
  }
}