clarify "require-instance" property for leafrefs

[abierman]

There are some issues with "require-instance" processing for leafrefs
It is clear that this property is enforced in a valid data tree [9.9, para 2]

• path statement validation [9.9.2, para 4]

The "path" expression evaluates to a node set consisting of zero,
one, or more nodes. If the "require-instance" property is "true",
this node set MUST be non-empty.

Should be clear that "the node set" refers to conceptual evaluation of the path-expr
using an instance of the object defined in this data-def-stmt

When is the node-set evaluated? Also only in a valid data tree, but not stated

There is an example [9.12.4] that warns not to delete a pointed-at leaf in use
but no example of the error that would be returned

• Error handling for deletion of pointed-at leaf [15.5]

15.5. Error Message for Data That Violates a "require-instance" Statement
If a NETCONF operation would result in configuration data where a
leaf of type "instance-identifier" or "leafref" marked with
require-instance "true" refers to an instance that does not exist,
the following error MUST be returned:
error-tag: data-missing
error-app-tag: instance-required
error-path: Path to the instance-identifier or leafref leaf.

This error handling is clear for create and modify operations on the leafref leaf,
but not clear for modify and delete operations on the pointed-at leaf.

Consider the example in 9.12.4.

Assume a delete edit-config operation on the "filter" entry.
If this is done on candidate then the delete is allowed.
During a validate or commit operation, the error reporting in [15.5] is followed.
The error-path should be /outbound-filter

What is the error handling for target = running?
In this case the delete operation is not allowed since edits on running must be valid immediately.
Is the same error-reporting followed as in candidate, or is an "in-use" error-tag used
and the error-path set to /filter/name

[mbj4668]

There are some issues with "require-instance" processing for leafrefs
It is clear that this property is enforced in a valid data tree [9.9, para 2]

* path statement validation [9.9.2, para 4]

The "path" expression evaluates to a node set consisting of zero,
one, or more nodes. If the "require-instance" property is "true",
this node set MUST be non-empty.

Should be clear that "the node set" refers to conceptual evaluation of the path-expr
using an instance of the object defined in this data-def-stmt

When is the node-set evaluated? Also only in a valid data tree, but not stated

The intention is that section 8.3.3 covers this. If it is unlcear then we should clarify.

There is an example [9.12.4] that warns not to delete a pointed-at leaf in use
but no example of the error that would be returned

* Error handling for deletion of pointed-at leaf [15.5]

15.5. Error Message for Data That Violates a "require-instance" Statement
If a NETCONF operation would result in configuration data where a
leaf of type "instance-identifier" or "leafref" marked with
require-instance "true" refers to an instance that does not exist,
the following error MUST be returned:
error-tag: data-missing
error-app-tag: instance-required
error-path: Path to the instance-identifier or leafref leaf.

This error handling is clear for create and modify operations on the leafref leaf,
but not clear for modify and delete operations on the pointed-at leaf.

This text says "a NETCONF operation would result in..." which is intended to capture also the delete case.

Consider the example in 9.12.4.

Assume a delete edit-config operation on the "filter" entry.
If this is done on candidate then the delete is allowed.
During a validate or commit operation, the error reporting in [15.5] is followed.
The error-path should be /outbound-filter

Yes.

What is the error handling for target = running?
In this case the delete operation is not allowed since edits on running must be valid immediately.
Is the same error-reporting followed as in candidate

Yes, since 15.5 applies.

[abierman]

OK -- closing this issue since no changes required