Add flag to enforce subdirectory == subdirectory in index.json

[dholth]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

It can cause problems when a package is built for a subdirectory but is placed into a different subdirectory (e.g. a linux-64 package copied into noarch/)

Add a strict flag to either error or ignore those packages when index.json's subdir does not match. Then a mismatched package would not show up in repodata.json.

Remember that old packages might have a platform= in index.json or nothing at all? instead of subdir.

[kenodegard]

See recent incident on conda-forge: conda-forge/status#144

[kenodegard]

I'm thinking this check should be enabled by default with the option to disable

[wolfv]

Sounds reasonable to me. I think it should also emit a warning (or maybe even error?).

[dholth]

Is it correct that within the last year libmamba promoted "subdir mismatch" as something to crash on, which was not previously the case?

[kenodegard]

Not libmamba, libsolv

[wolfv]

Yeah, libsolv added this check at some point. I didn't ever think that it would be possible to have mixed-arch packages in the subdirs though.

[dholth]

When developing conda-index it was really useful to use ~/miniconda3/pkgs/cache as something to index (these are not split out by subdir). Maybe not a common case, I wonder if we could handle these intelligently by automatically splitting them into their proper subdirectories.