## Summary
The behavior is as follows:
- If you provide `--index` or `--default-index` on the command-line, we
add those indexes to the `pyproject.toml` (with names, if provided, as
in `--index pytorch=https://download.pytorch.org/whl/cu121`.
- If you provide `--index-url` or `--default-index`, we warn, but don't
add the indexes to the file. (This seems wrong -- why not add them?)
- If you provide an index with a name or URL that already exists, we
remove that entry, and add the new index to the top of the list (since
it now has highest priority).
- If you provide a `--default-index`, and an index already has `default
= true`, we remove that entry, since it won't be used anymore.
We do _not_ pin packages to specific indexes yet.
Charlie Marsh
ad24cee7c6