[Python] uv `required-environments`: only require that some extras build in some environments

cross-posted to the uv issue tracker

As all dependency problems, this one originates from torch.

I need to support cuda 12.4 on x86_64, and cuda 12.8 on arm64. Importantly, pytorch does not provide builds for cuda 12.4 on arm64 platforms.

so I wrote my pyproject.toml the following way, using, specifying the extra field in required-environments to limit which version of cuda uv would try to resolve for depending on which platform

[project]
name = "minimal_reproduction"
version = "0.1.0"
description = ""
readme = "README.md"
requires-python = ">=3.13"
dependencies = []

[tool.uv]
conflicts = [
[{extra="cu128"}, {extra="cu124"}]
]
required-environments = [
"sys_platform == 'linux' and platform_machine == 'x86_64' and extra == 'cu124'",
"sys_platform == 'linux' and platform_machine == 'aarch64' and extra == 'cu128'",
]
index-strategy = "unsafe-best-match"



[project.optional-dependencies]
cu124 = [
"torch==2.6.0+cu124",
]

cu128 = [
"torch==2.7.0+cu128",
]

[[tool.uv.index]]
name = "torch-cu128"
url = "https://download.pytorch.org/whl/cu128"

[[tool.uv.index]]
name = "torch-cu124"
url = "https://download.pytorch.org/whl/cu124"


But it seems uv ignores the extra field, and still complains that it cannot build cu124 on arm

× No solution found when resolving dependencies for split (python_full_version ==
│ '3.13.*' and platform_machine == 'aarch64' and sys_platform == 'linux' and extra ==
│ 'cu128'):
╰─▶ Because torch==2.6.0+cu124 has no `python_full_version == '3.13.*' and
platform_machine == 'aarch64' and sys_platform == 'linux' and extra ==
'cu128'`-compatible wheels and test[cu124] depends on torch==2.6.0+cu124, we can
conclude that test[cu124]'s requirements are unsatisfiable.
And because your project requires test[cu124], we can conclude that your project's
requirements are unsatisfiable.

hint: The resolution failed for an environment that is not the current one, consider
limiting the environments with `tool.uv.environments`.


Is there a way to limit which extras uv will try to build on certain environments?

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