diff gives orig-value not value attribute on delete..

[hyberdk]

This is related to #2475, but I thought it might be better to keep it clean as I think this might be a bug.

Im sorry but I dont do C, so I replicated it with the libyang-python module. Im sure this can easily be reproduced in C as I dont believe this is a problem within libyang-python.

Im using libyang 4.2.2 with the latest master version of libyang-python

the model Im using is this:

module leaf-list-test {
  namespace "urn:test:leaf-list-test";
  prefix llt;

  container system {
    leaf-list ordered-names {
      type string;
      ordered-by user;
    }
  }
}

my code looks like this:

from libyang import Context

running_xml = """
<system xmlns="urn:test:leaf-list-test">
    <ordered-names>alpha</ordered-names>
    <ordered-names>bravo</ordered-names>
    <ordered-names>charlie</ordered-names>
    <ordered-names>delta</ordered-names>
    <ordered-names>echo</ordered-names>
</system>
"""

intent_xml = """
<system xmlns="urn:test:leaf-list-test">
    <ordered-names>new_alpha</ordered-names>
    <ordered-names>bravo</ordered-names>
    <ordered-names>charlie</ordered-names>
    <ordered-names>echo</ordered-names>
    <ordered-names>foxtrot</ordered-names>
</system>
"""
this_path = __file__.rsplit("/", 1)[0]
ctx = Context(this_path)
ctx.load_module("leaf-list-test")

running = ctx.parse_data_mem(running_xml, "xml", strict=True, no_state=True, validate_present=True)
intent = ctx.parse_data_mem(intent_xml, "xml", strict=True, no_state=True, validate_present=True)

diff = running.diff(intent)

print(running.print_mem("xml", pretty=True))
print(intent.print_mem("xml", pretty=True))
print(diff.print_mem("xml", pretty=True))

When I run it, it gives me this output (print of running, intent and diff)

<system xmlns="urn:test:leaf-list-test">
  <ordered-names>alpha</ordered-names>
  <ordered-names>bravo</ordered-names>
  <ordered-names>charlie</ordered-names>
  <ordered-names>delta</ordered-names>
  <ordered-names>echo</ordered-names>
</system>

<system xmlns="urn:test:leaf-list-test">
  <ordered-names>new_alpha</ordered-names>
  <ordered-names>bravo</ordered-names>
  <ordered-names>charlie</ordered-names>
  <ordered-names>echo</ordered-names>
  <ordered-names>foxtrot</ordered-names>
</system>

<system xmlns="urn:test:leaf-list-test" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:operation="none">
  <ordered-names yang:operation="delete" yang:orig-value="">alpha</ordered-names>
  <ordered-names yang:operation="delete" yang:orig-value="charlie">delta</ordered-names>
  <ordered-names yang:operation="create" yang:value="">new_alpha</ordered-names>
  <ordered-names yang:operation="create" yang:value="echo">foxtrot</ordered-names>
</system>

I could obviously be wrong here, but from what I can deduct, then the yang:value is the internal placement in libyang. It would be the same as yang:insert="after" yang:value="whatever" The difference is that libyang has implicit yang:insert="after"and if its the first item in the list then yang:value=""

This is consistent of how it works on a list, but the problem I face is on a leaf-list then doing the yang:operation="delete" operation it uses the yang:orig-value="" or yang:orig-value="whatever"..

just to carve it out into wet cardboard, then this is what I get:

<system xmlns="urn:test:leaf-list-test" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:operation="none">
  <ordered-names yang:operation="delete" yang:orig-value="">alpha</ordered-names>                <---------- Notice this is orig-value
  <ordered-names yang:operation="delete" yang:orig-value="charlie">delta</ordered-names>     <---------- Notice this is orig-value
  <ordered-names yang:operation="create" yang:value="">new_alpha</ordered-names>
  <ordered-names yang:operation="create" yang:value="echo">foxtrot</ordered-names>
</system>

and this is what I expect:

<system xmlns="urn:test:leaf-list-test" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:operation="none">
  <ordered-names yang:operation="delete" yang:value="">alpha</ordered-names>                  <---------- Notice this is value now
  <ordered-names yang:operation="delete" yang:value="charlie">delta</ordered-names>       <---------- Notice this is value now
  <ordered-names yang:operation="create" yang:value="">new_alpha</ordered-names>
  <ordered-names yang:operation="create" yang:value="echo">foxtrot</ordered-names>
</system>

When creating a new entry, it seems correct and as I said before the behaviour for list also seems to follow this approach (when deleting an item, it uses value="" if its index=0)

Hope it makes sense.

Esben