chore: transition the library to microgenerator

[plamut]

Closes #41.

Remaining things:

• Add the UPGRADING guide to docs.

[plamut]

I see potential issues with namespace clashes.

The following imports used with the old generated client do not work anymore:

from google.cloud import bigquery_datatransfer
from google.cloud import bigquery_datatransfer_v1

These imports need to be changed to the following:

from google.cloud.bigquery import datatransfer
from google.cloud.bigquery import datatransfer_v1

This is all well and good, but if one then installs google-cloud-bigquery, these imports stop working:

$ pip install google-cloud-bigquery
$ python3.8
...
>>> from google.cloud.bigquery import datatransfer
ImportError: cannot import name 'datatransfer' from 'google.cloud.bigquery'

Uninstalling google-cloud-bigquery makes the datatransfer import work again.

@busunkim96 Do you maybe know if any other 100% autogenerated libraries experienced the same problem and how they fixed it?

Edit:
And just when I typed the word "namespace", I got an idea that worked - google.cloud.bigquery needs to be added to namespace packages in setup.py:

namespaces.append("google.cloud.bigquery")

[busunkim96]

@plamut @tswast If you all prefer to retain the old namespacing you can do that via generator args

https://github.com/googleapis/googleapis/blob/b821f320473c8ec05a1c7fb9a496c958b1ab9834/google/devtools/clouderrorreporting/v1beta1/BUILD.bazel#L161

opt_args = ["python-gapic-namespace=google.cloud", "python-gapic-name=bigquery_datatransfer"],

Not sure where we landed with the other BigQuery libraries though, I assume it's better for them to be consistent?

[danoscarmike]

Thanks @plamut! I'll defer to @busunkim96 and @tswast on this one.

[tswast]

Not sure where we landed with the other BigQuery libraries though, I assume it's better for them to be consistent?

https://github.com/googleapis/python-bigquery-reservation and https://github.com/googleapis/python-bigquery-connection both use the google.cloud.bigquery namespace. (They might actually not be working properly, as I haven't tested them yet)

[plamut]

OK, I'll keep the google.cloud.bigquery namespace then and document it in the UPGRADING guide accordingly.

[plamut]

Added the UPGRADING guide and simplified the sample, the PR should be done now.

After approving and merging, I will follow up with a release PR (probably on Monday).

[busunkim96]

The generator isn't adding the async client to __init__.py?

[plamut]

IIRC something tried to import an Async client somewhere, but it did not exist, thus added this import.

Edit: Misunderstood. Yes, that import was missing, thus added it manually. I probably forgot to open an issue?

Edit 2: This was to make sure that datatransfer and datatransfer_v1 are the same (one lacked the async client in __all__).