Different resolution failure messages on different verbosity

• pip version: 21.0.1
• Python version: 3.6 (but 3.7 and 3.8 have the same problem)
• Operating system: Linux (Debian buster docker image)

PIP 21.0.1 sometimes produces wrong error about conflicts , and it produces different (correct!) error when -vvvv options are added.

This problem originated with https://github.com/apache/airflow/issues/15463 (you can see history of it there). We have quite complex dependencies in Airlfow and we are still recommending people to install airflow with PIP 20.2.4, but we are hoping to get rid of that limitation, one problem however was a very strange one and we did not have time to look at it - but when I looked today I realized that the error printed by PIP was misleading (as I could not see the reason for the original error).

I believe PIP instead of pyarrow reports google-cloud-bigquery-storage as having a problem. Looks like instead of printing the actual dependency that has a problem, it prints the “sibling” of that dependency (or smth like that).

It is very easily reproducible:

1. Run: pip install apache-airflow[google]==2.0.2 --constraint https://raw.githubusercontent.com/apache/airflow/constraints-2.0.2/constraints-3.6.txt

You should get an error:

ERROR: Could not find a version that satisfies the requirement google-cloud-bigquery-storage<2.0.0dev,>=1.0.0; extra == "bqstorage" (from google-cloud-bigquery[bqstorage,pandas])

1. Run pip install -vvvv apache-airflow[google]==2.0.2 --constraint https://raw.githubusercontent.com/apache/airflow/constraints-2.0.2/constraints-3.6.txt

You should get an error:

ERROR: Could not find a version that satisfies the requirement pyarrow<2.0dev,>=1.0.0; extra == "bqstorage" (from google-cloud-bigquery[bqstorage,pandas])
ERROR: No matching distribution found for pyarrow<2.0dev,>=1.0.0; extra == "bqstorage"

I believe in both cases we ONLY have problem with pyarrow, and it is misreported without the -vvvv flag. Looks like instead of actual dependency that is wrong (pyarrow), the sibling of that dependency (google-cloud-bigquery-storage) is printed out by PIP. Note that other than the dependency - those are the very same limits which are problematic (<2.0.0dev,>=1.0.0; extra == “bqstorage”).

I also could not find any other packages from those being installed where google-cloud-bigquery-storage would be limited to <2.0.0dev,>=1.0.0 - that’s why I think this is a bug in PIP.

Gists with the outputs to compare

pip install apache-airflow[google]==2.0.2 --constraint https://raw.githubusercontent.com/apache/airflow/constraints-2.0.2/constraints-3.6.txt :

Here: https://gist.github.com/potiuk/04f6127469a709e3e47be7585c9a863c

pip install -vvvv apache-airflow[google]==2.0.2 --constraint https://raw.githubusercontent.com/apache/airflow/constraints-2.0.2/constraints-3.6.txt:

https://gist.github.com/potiuk/17a3d591fb091bdd8a0e213f49b6b0af

I might be wrong, of course, but it looks like this.

UPDATE:

I run it with -vv and it fails with the 'google-cloud-bigquery-storage` error: https://gist.github.com/potiuk/2f9af6a8eaac7ea393fd1f9fe64361c7

The -v and -vvv both fail with pyarrow error.

In neither of those I can find where the google-cloud-bigquery-storage<2.0.0dev,>=1.0.0; extra == "bqstorage" (from google-cloud-bigquery[bqstorage,pandas]) comes from 😦.

[uranusjr]

So it turns out the different error message is due to pkg_resources returns dependencies in indeterministic ordering (because internally it uses set to store those). When the ordering is different, the resolver can be sent down to subtrees in different orders, and report different errors if you have multiple conflicts in the dependency graph.

I think we should sort the dependencies somehow (maybe just alphabetically), this would be good for debuggability, if nothing else.

[uranusjr]

constraints-3.6.txt

Above is a snapshot of the constraints-3.6.txt file that caused the issue, for future reproduction. I’m assuming the file hosted in Airflow’s repo will be overwritten once you sort out the conflicts.