Can I use tach to limit which project-internal modules can import a specific external dependency?

[menzenski]

Given the following hypothetical project, where there is common/shared functionality defined in some modules, and custom/non-shared functionality defined in others:

my_project
├── common
│   └── datastore
│       └── aws_s3_datastore.py
└── reports
    ├── report_a.py
    └── report_b.py

I know that I can use tach to define/enforce behavior between my project-internal modules (and indeed we are using tach for this purpose today). We can mark aws_s3_datastore, report_a, and report_b as tach modules and allow report_a and report_b to depend on aws_s3_datastore and not on each other.

I'm interested to know if I can define interactions between internal modules and external dependencies in the same way. For example: could I use tach to enforce that the aws_s3_datastore module can reference the external boto3 package, while report_a and report_b modules can not?

It seems like #683 allows me to do this (or if not this specifically, something that's probably close enough). Is that accurate?

[emdoyle]

Yes, if I understand correctly -- you should use cannot_depend_on_external = ["boto3"] on the report_a and report_b modules. By default it would be allowed in the aws_s3_datastore module, so using depends_on_external there would be more trouble than it's worth (it would need to know all the expected third party dependencies for that module).

[menzenski]

Ok, thanks - I had been concerned I would need to list all third-party dependencies in order to do this, but if I can just configure the other modules not to depend on boto3 that would do what I need.