Adding custom links between sibling catalogs creates absolute HREFs

[constantinius]

In the following example, we have a root catalog which includes two sub-catalogs a and b. I now want to highlight a reference between the two siblings, which cannot be replaced by a parent-child link:

import pystac

root = pystac.Catalog("root", "root")
a = pystac.Catalog("a", "a")
b = pystac.Catalog("b", "b")

root.add_child(a)
root.add_child(b)

a.add_link(pystac.Link("related", b))

root.normalize_and_save("test_out", pystac.CatalogType.SELF_CONTAINED)

Even when I now save it as "self-contained", I now have an absolute link from a to b:

{
  "type": "Catalog",
  "id": "a",
  "stac_version": "1.0.0",
  "description": "a",
  "links": [
    {
      "rel": "root",
      "href": "../catalog.json",
      "type": "application/json"
    },
    {
      "rel": "related",
      "href": "/home/<user>/test_out/b/catalog.json"
    },
    {
      "rel": "parent",
      "href": "../catalog.json",
      "type": "application/json"
    }
  ],
  "stac_extensions": []
}

I would have expected something like that:

...
   {
      "rel": "related",
      "href": "../b/catalog.json"
    },
...

I can't seem to get rid of the absolute links, even when using stac copy or similar commands.

[constantinius]

I found the following workaround (fix?)

if "related" not in pystac.link.HIERARCHICAL_LINKS:
    pystac.link.HIERARCHICAL_LINKS.append("related")

[gadomski]

It does seem reasonable to expect normalization to resolve all object hrefs the same way (relative or absolute). Thanks for the report.