Add warning when dependencies are empty with Poetry metadata

[yasufumy]

Resolve #1630

PyProjectToml doesn't seem to have a tool field, so instead of checking it, I check if requirements is empty.

uv/crates/uv-build/src/lib.rs

Lines 176 to 184 in c04f597

	/// A pyproject.toml as specified in PEP 517
	#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
	#[serde(rename_all = "kebab-case")]
	pub struct PyProjectToml {
	/// Build-related data
	pub build_system: Option<BuildSystem>,
	/// Project metadata
	pub project: Option<Project>,
	}

[zanieb]

Could we move this down and make it conditional on requirements being empty? It's possible that they've added a dependency section we can read even if they're using Poetry.

We have a similar warning for requirements.txt files

uv/crates/requirements-txt/src/lib.rs

Lines 317 to 322 in 2ea44d8

	if data == Self::default() {
	warn_user!(
	"Requirements file {} does not contain any dependencies",
	requirements_txt.as_ref().display()
	);
	}

Maybe we can phrase it the same with a hint that we can't read Poetry's dependencies?

[charliermarsh]

(Is it possible to make this conditional on whether tool.poetry.dependencies is populated? I assume not, since we don't include that in TOML schema. If so, this is totally fine.)

[yasufumy]

@zanieb Thank you for your suggestion. I updated my PR and also fixed a test case. Let me know if I miss anything!

@charliermarsh Thank you for your comment. Are you planning to support the poetry-style format? If so, and no one is working on it, I'm interested in contributing.

[charliermarsh]

Thanks!

[hauntsaninja]

Maybe this should be more specific, e.g. hint: specify dependencies in project.dependencies section, tool.poetry.dependencies is not currently supported. I can imagine users taking "Poetry's format" to mean all kinds of things, like literally the use of pyproject.toml

[charliermarsh]

Nice idea: #1730