check-external reporting dependencies as unused

[EArbeitman]

Hi Team,

I'm reconciling our dependencies and noticed some unexpected behavior when running tach check-external.

> tach check-external

❌ Error: External package 'strawberry_graphql' is not used in package 'personalization'.

Here is the pyproject.toml file for personalization

[project]
name = "personalization"
version = "0.1.0"
authors = [
    { name = "frenata" }
]
dependencies = [
    ### if you are importing any local packages you can add them here manually like this:
    "fastapi[standard]>=0.115.6",
    "strawberry-graphql[fastapi]>=0.254.0",
    "strawberry-sqlalchemy-mapper>=0.5.0",
    "strawberry",

    ## local stuff
    "debtsy_db",
    "observability",
	"debt_segment_controller",
	"debt_controller",
	"client_controller",
	"personalization_service",
    
]
requires-python = ">= 3.9.15"

[project.scripts]
# TODO Change run-project to be a bit more descriptive and update in the Dockerfile
main = "personalization.run:main"

[tool.rye]
managed = true
dev-dependencies = [
    "pipdeptree>=2.24.0",
    "ruff>=0.8.3",
    "pytest>=8.3.4",
]

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

And here is a snippet of code that uses strawberry

#src/apps/src/personalization/schema.py

import strawberry
from debtsy_db import models
from observability.tracer import add_tags
from personalization_service import personalization_service
from strawberry_sqlalchemy_mapper import StrawberrySQLAlchemyMapper

strawberry_sqlalchemy_mapper = StrawberrySQLAlchemyMapper()


@strawberry_sqlalchemy_mapper.type(models.debt_segment.DebtSegment)
...
...
...

Here is the contents of my tach.toml file

source_roots = [
    "apps/*/src",
    "apps/*/libs/*/src",
    "apps/*/utils/*/src",
    "apps/*/src/models/src",
    "apps/*/src",
    "apps/debtsy/src/*",
    "domains/*/src"

]

# [[modules]]
# path = "temporal"
# cannot_depend_on_external = ["debtsy", "debtsy_db", "base_config"]

[emdoyle]

Hey, thanks for raising this.

In this example, Tach would determine that import strawberry refers only to the "strawberry" dependency, not the "strawberry-graphql" dependency, which would mean that the graphql dependency seems unused. If the graphql dependency is in a sense implicit and won't be seen in direct imports, you can add it to external.exclude (docs here https://docs.gauge.sh/usage/configuration#external).

If this is happening with other deps, it could also be a mismatch between the distribution name (in the dependencies list) and the actual imported module name (in your source code). This can be handled with the rename config: https://docs.gauge.sh/usage/configuration#external