Documentation xref user lists depend on registration order

[orting]

Summary

reference.pdf cross-reference user lists can change depending on registration/traversal order, even when the documented model content is unchanged.

Root cause

The documentation cross-reference builder stores model users in std::set<XRef::ModelUser>, but XRef::ModelUser::operator< in src/object_model/xref.C compares only:

• component
• model

It does not compare the path field.

That means distinct uses of the same model from different parameter paths collapse into a single set entry, and whichever path is visited first wins. After the explicit-registration rewrite changed traversal/registration timing, the surviving entry changed in generated docs.

Example

For vegetation afforestation, both litter_am and root_am are AOM objects, but the generated reference can show either:

• vegetation afforestation root am
• vegetation afforestation litter am

depending on traversal order.

This was observed as a documentation diff while checking that generated PDFs remain stable across the explicit-registration refactor.

Why this matters

The documentation output should not depend on registration order when the underlying semantics are unchanged. Today it can, because xref deduplication is path-insensitive.

Proposed fix

Include path in XRef::ModelUser::operator< so the set ordering and uniqueness account for the full usage location, not just (component, model).

That should make the cross-reference data structurally correct and prevent registration-order-dependent user-list differences in the generated documentation.

Relevant code

• src/object_model/xref.C
• include/object_model/xref.h
• src/programs/program_document.C