Update ABI3 documentation

[wolfv]

We found a few problems with py-rattler ABI3 packages. It would be good to update the docs or improve the docs to also include the new findings:

https://github.com/conda-forge/py-rattler-feedstock/pull/42

Cross-compiling: ignore run exports coming from cross-python_${{ target_platform }}. Do not depend on bare python in run to avoid python pin.

[travishathaway]

Just wanted to chime in here because I'm having some trouble with what rattler-build produces when I try to build abi3 python packages.

I get the following in index.json:

{
  "arch": "x86_64",
  "build": "h81b34b9_0",
  "build_number": 0,
  "constrains": [
    "__glibc >=2.17"
  ],
  "depends": [
    "python >=3.9",
    "conda >=24.11.0",
    "click",
    "_python_abi3_support 1.*",
    "python >=3.13",
    "openssl >=3.4.1,<4.0a0"
  ],
  "name": "conda-rlock",
  "noarch": "python",
  "platform": "linux",
  "subdir": "linux-64",
  "timestamp": 1741646816508,
  "version": "0.1.0"
}

The strange part is that Python appears twice (python >= 3.9 and python >=3.13).

My recipe is here:

• https://github.com/travishathaway/conda-rlock/tree/main/recipe

And this was the output at the end of rattler-build:

 │ │ ╭──────────────────────┬────────────────────────────────────────╮
 │ │ │ Name                 ┆ Spec                                   │
 │ │ ╞══════════════════════╪════════════════════════════════════════╡
 │ │ │ Run dependencies     ┆                                        │
 │ │ │ python               ┆ >=3.9                                  │
 │ │ │ conda                ┆ >=24.11.0                              │
 │ │ │ click                ┆                                        │
 │ │ │ _python_abi3_support ┆ 1.* (RE of [host: python-abi3])        │
 │ │ │ python               ┆ >=3.13 (RE of [host: python-abi3])     │
 │ │ │ openssl              ┆ >=3.4.1,<4.0a0 (RE of [host: openssl]) │
 │ │ │                      ┆                                        │
 │ │ │ Run constraints      ┆                                        │
 │ │ │ __glibc              ┆ >=2.17 (RE of [build: rust_linux-64])  │
 │ │ ╰──────────────────────┴────────────────────────────────────────╯
 │ │ 

[wolfv]

Yes, I think you need to select a version of python-abi3 that corresponds to your lower bound of Python ...

[travishathaway]

That make sense. So, if I have this in my Cargo.toml:

[dependencies]
pyo3 = { version = "0.23.4", features = ["extension-module", "abi3-py39"] }  # Python 3.9

Then I have to have the following in the recipe:

   # ... snip
      host:
        - python >=3.9
        - python-abi3 =3.9
   # ... snip

The only thing that's still a little confusing is that python appears twice in the run dependencies at the end. I was able to work around that by simply leaving python out of the run section because it gets added later.

[wolfv]

I updated the docs and we also fixed the additional python ignore