feat: Implement PEP735 support

[olivier-lacroix]

Fixes #2256 as well as #2149 (maybe we want to create a separate issue to interpret / use markers).

This PR adds handling of [dependency-groups] in pyproject.toml:

• any group in this table is interpreted as a feature by pixi (similar to current behaviour for optional-dependencies)
• if a dependency group and a group of optional dependencies have the same name, all dependencies will be added to a single common feature

This PR also changes the behaviour of pixi add --pypi in case of a pyproject.toml manifest:

• if a feature is specified, the dependency is now added to the [dependency-groups] table instead of the [optional-dependencies] table currently
• if --platform or --editable is specified, the pypi dependency will be added to the tool.pixi.pypi-dependencies table instead, since native arrays have no support for platform-specific or editable dependencies.
• it adds a --location argument:
  • Specifiying --location to pixi will force adding the pypi dependency to the tool.pixi.pypi-dependencies table.
  • Specifying --location to optional-dependencies will force adding the pypi dependency to the project.optional-dependencies table (this will only have an effect if a non-default feature is also specified).

This PR also changes the behaviour of pixi init when strating from an existing pyproject.toml manifest:

• one environment per dependency-group will be added to the environments table, similar to what is being done currently with groups of optional dependencies.

As a drive-by improvement, when removing a pypi dependency from a pyproject.toml manifest, any empty array will be deleted.

[ruben-arts]

First off, thank you 💯, amazing contribution! Well documented, Kudos!

I have a few small requests to finish it off.

Also could it print in what location it was added in the pixi add output. e.g.:

❯ pixi add --pypi --location optional-dependencies boltons
✔ Added boltons >=24.1.0, <25
Added these to `optional-dependencies`.

❯ pixi add --pypi numpy
✔ Added numpy >=2.1.3, <3
Added these as `project.dependencies`.

❯ pixi add --pypi --feature test pytest
✔ Added numpy >=2.1.3, <3
Added these as `dependency-groups`.

[ruben-arts]

What about adding the dependencies-groups here as well so you are allowed to be explicit?

[olivier-lacroix]

Sure

[ruben-arts]

This location thing works but confused me a little as it is also required in combination with --feature
What if we instead extend the CLI with --optional-dependencies [OPTIONAL_GROUP] --dependency-group [DEPENDENCY_GROUP] and only force it into tool.pixi if it has a --editable or --platform

Then it would result in this:

> pixi add --pypi numpy
> pixi add --pypi --optional-dependencies cuda torch
> pixi add --pypi --dependency-group test pytest
> pixi add --pypi "package @ PATH" --editable
> pixi add --pypi --platform linux-64 cmake
> pixi add --pypi --feature sql postgresql-api
> pixi add --pypi --feature default click

[project]
dependencies = ["numpy>=2.1.3,<3"]

[project.optional-dependencies]
cuda = ["torch>=a.b.c, <b"]

[dependency-groups]
test = ["pytest>=8.3.3,<9"]

[tool.pixi.pypi-dependencies]
package = { path = "PATH", editable = true }

[tool.pixi.target.linux-64.pypi-dependencies]
cmake =  ">=a.b.c, <b"

[tool.pixi.feature.sql.pypi-dependencies]
postgresql-api =  ">=a.b.c, <b"

[tool.pixi.pypi-dependencies]
click = ">=a.b.c, <b"

EDIT: added the --feature definition

[olivier-lacroix]

Yes, that may be a better option. Two questions @ruben-arts

• This would mean one could not force the dependency to be added to the tool.pixi.pypi-dependencies table; Is that OK? Note that with this PR, it is possible, for both default or non-default features
• What would happen if one specifies a —feature ?

[ruben-arts]

Features are pixi only so lets make that the tool.pixi.feature.name.pypi-dependencies.
I don't have an opinionated answer for the first question but we could just allow --feature default to force it into tool.pixi.pypi-dependencies.
I added it to this initial post, let me know what you think.