Platform-specific overrides for environment variables

[JP-Ellis]

Summary

How do I set environment variables based on the platform?

Details

I am building a package which contains a Python C extension which is dynamically linked to a library. In the wheel-building process, there's no issue as the wheel-repair functionality bundles the library into the wheel and modifies the RPATH (or something similar).

The issue comes from editable installs, whereby the library path environment variable needs to be set.

I was expecting something like this would work:

[tool.hatch.envs.default.overrides]
platform.linux.env-vars   = { LD_LIBRARY_PATH = "{root}/src/pact_ffi:{env:LD_LIBRARY_PATH}" }
platform.macos.env-vars   = { DYLD_LIBRARY_PATH = "{root}/src/pact_ffi:{env:DYLD_LIBRARY_PATH}" }
platform.windows.env-vars = { PATH = "{root}/src/pact_ffi;{env:PATH}" }

but this produces the following error:

TypeError: Field `tool.hatch.envs.default.overrides.platform.macos.env-vars` must be a string or an array

Work-around

The only workaround at the moment is to set all these variables for all platforms. While that works, it seems suboptimal, especially since Windows' PATH modification could cause issues on macOS or Linux.

[ShreeChaturvedi]

env-vars overrides take KEY=VALUE strings (or an array of those), not a TOML table. That is why the map form raised must be a string or an array.

[tool.hatch.envs.default.overrides]
platform.linux.env-vars = "LD_LIBRARY_PATH={root}/src/pact_ffi{;}{env:LD_LIBRARY_PATH:}"
platform.macos.env-vars = "DYLD_LIBRARY_PATH={root}/src/pact_ffi{;}{env:DYLD_LIBRARY_PATH:}"
platform.windows.env-vars = "PATH={root}/src/pact_ffi{;}{env:PATH:}"

Array form if you want:

platform.linux.env-vars = [
  { key = "LD_LIBRARY_PATH", value = "{root}/src/pact_ffi{;}{env:LD_LIBRARY_PATH:}" },
]

Docs: https://hatch.pypa.io/latest/config/environment/advanced/#types

Pitfall: bare {env:LD_LIBRARY_PATH} errors if unset. Use {env:NAME:} for an empty default. {;} is the OS path separator.