Improve static metadata extraction for Poetry projects (#4182)

## Summary

Adds handling for a few cases to improve interoperability with Poetry:

- If the `project` schema is invalid, we now raise a hard error, rather
than treating the metadata as dynamic and then falling back to the build
backend. This could cause problems, I'm not sure. It's stricter than
before.
- If the project contains `tool.poetry` but omits
`project.dependencies`, we now treat it as dynamic. We could go even
further and treat _any_ Poetry project as dynamic, but then we'd be
ignoring user-declared dependencies, which is also confusing.

Closes #4142.

crates/pypi-types/src/metadata.rs

@@ -60,6 +60,8 @@ pub enum MetadataError {
     UnsupportedMetadataVersion(String),
     #[error("The following field was marked as dynamic: {0}")]
     DynamicField(&'static str),
+    #[error("The project uses Poetry's syntax to declare its dependencies, despite including a `project` table in `pyproject.toml`")]
+    PoetrySyntax,
 }
 
 impl From<Pep508Error<VerbatimParsedUrl>> for MetadataError {
@@ -210,6 +212,15 @@ impl Metadata23 {
             }
         }
 
+        // If dependencies are declared with Poetry, and `project.dependencies` is omitted, treat
+        // the dependencies as dynamic. The inclusion of a `project` table without defining
+        // `project.dependencies` is almost certainly an error.
+        if project.dependencies.is_none()
+            && pyproject_toml.tool.and_then(|tool| tool.poetry).is_some()
+        {
+            return Err(MetadataError::PoetrySyntax);
+        }
+
         let name = project.name;
         let version = project
             .version
@@ -257,11 +268,11 @@ impl Metadata23 {
 }
 
 /// A `pyproject.toml` as specified in PEP 517.
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Deserialize, Debug)]
 #[serde(rename_all = "kebab-case")]
 struct PyProjectToml {
-    /// Project metadata
     project: Option<Project>,
+    tool: Option<Tool>,
 }
 
 /// PEP 621 project metadata.
@@ -270,7 +281,7 @@ struct PyProjectToml {
 /// relevant for dependency resolution.
 ///
 /// See <https://packaging.python.org/en/latest/specifications/pyproject-toml>.
-#[derive(Deserialize, Debug, Clone)]
+#[derive(Deserialize, Debug)]
 #[serde(rename_all = "kebab-case")]
 struct Project {
     /// The name of the project
@@ -288,6 +299,17 @@ struct Project {
     dynamic: Option<Vec<String>>,
 }
 
+#[derive(Deserialize, Debug)]
+#[serde(rename_all = "kebab-case")]
+struct Tool {
+    poetry: Option<ToolPoetry>,
+}
+
+#[derive(Deserialize, Debug)]
+#[serde(rename_all = "kebab-case")]
+#[allow(clippy::empty_structs_with_brackets)]
+struct ToolPoetry {}
+
 /// Python Package Metadata 1.0 and later as specified in
 /// <https://peps.python.org/pep-0241/>.
 ///
@@ -369,6 +391,15 @@ impl RequiresDist {
             }
         }
 
+        // If dependencies are declared with Poetry, and `project.dependencies` is omitted, treat
+        // the dependencies as dynamic. The inclusion of a `project` table without defining
+        // `project.dependencies` is almost certainly an error.
+        if project.dependencies.is_none()
+            && pyproject_toml.tool.and_then(|tool| tool.poetry).is_some()
+        {
+            return Err(MetadataError::PoetrySyntax);
+        }
+
         let name = project.name;
 
         // Extract the requirements.

crates/uv-distribution/src/error.rs

@@ -70,12 +70,12 @@ pub enum Error {
     NotFound(PathBuf),
     #[error("The source distribution is missing a `PKG-INFO` file")]
     MissingPkgInfo,
-    #[error("The source distribution does not support static metadata in `PKG-INFO`")]
-    DynamicPkgInfo(#[source] pypi_types::MetadataError),
+    #[error("Failed to extract static metadata from `PKG-INFO`")]
+    PkgInfo(#[source] pypi_types::MetadataError),
     #[error("The source distribution is missing a `pyproject.toml` file")]
     MissingPyprojectToml,
-    #[error("The source distribution does not support static metadata in `pyproject.toml`")]
-    DynamicPyprojectToml(#[source] pypi_types::MetadataError),
+    #[error("Failed to extract static metadata from `pyproject.toml`")]
+    PyprojectToml(#[source] pypi_types::MetadataError),
     #[error("Unsupported scheme in URL: {0}")]
     UnsupportedScheme(String),
     #[error(transparent)]

crates/uv-distribution/src/source/mod.rs

@@ -1411,7 +1411,16 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
 
                 return Ok(Some(metadata));
             }
-            Err(err @ (Error::MissingPkgInfo | Error::DynamicPkgInfo(_))) => {
+            Err(
+                err @ (Error::MissingPkgInfo
+                | Error::PkgInfo(
+                    pypi_types::MetadataError::Pep508Error(_)
+                    | pypi_types::MetadataError::DynamicField(_)
+                    | pypi_types::MetadataError::FieldNotFound(_)
+                    | pypi_types::MetadataError::UnsupportedMetadataVersion(_)
+                    | pypi_types::MetadataError::PoetrySyntax,
+                )),
+            ) => {
                 debug!("No static `PKG-INFO` available for: {source} ({err:?})");
             }
             Err(err) => return Err(err),
@@ -1427,7 +1436,16 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
 
                 return Ok(Some(metadata));
             }
-            Err(err @ (Error::MissingPyprojectToml | Error::DynamicPyprojectToml(_))) => {
+            Err(
+                err @ (Error::MissingPyprojectToml
+                | Error::PyprojectToml(
+                    pypi_types::MetadataError::Pep508Error(_)
+                    | pypi_types::MetadataError::DynamicField(_)
+                    | pypi_types::MetadataError::FieldNotFound(_)
+                    | pypi_types::MetadataError::UnsupportedMetadataVersion(_)
+                    | pypi_types::MetadataError::PoetrySyntax,
+                )),
+            ) => {
                 debug!("No static `pyproject.toml` available for: {source} ({err:?})");
             }
             Err(err) => return Err(err),
@@ -1602,7 +1620,7 @@ async fn read_pkg_info(
     };
 
     // Parse the metadata.
-    let metadata = Metadata23::parse_pkg_info(&content).map_err(Error::DynamicPkgInfo)?;
+    let metadata = Metadata23::parse_pkg_info(&content).map_err(Error::PkgInfo)?;
 
     Ok(metadata)
 }
@@ -1627,8 +1645,7 @@ async fn read_pyproject_toml(
     };
 
     // Parse the metadata.
-    let metadata =
-        Metadata23::parse_pyproject_toml(&content).map_err(Error::DynamicPyprojectToml)?;
+    let metadata = Metadata23::parse_pyproject_toml(&content).map_err(Error::PyprojectToml)?;
 
     Ok(metadata)
 }
@@ -1646,8 +1663,8 @@ async fn read_requires_dist(project_root: &Path) -> Result<pypi_types::RequiresD
     };
 
     // Parse the metadata.
-    let requires_dist = pypi_types::RequiresDist::parse_pyproject_toml(&content)
-        .map_err(Error::DynamicPyprojectToml)?;
+    let requires_dist =
+        pypi_types::RequiresDist::parse_pyproject_toml(&content).map_err(Error::PyprojectToml)?;
 
     Ok(requires_dist)
 }

crates/uv/tests/pip_compile.rs

@@ -615,6 +615,110 @@ build-backend = "poetry.core.masonry.api"
     Ok(())
 }
 
+/// Compile a `pyproject.toml` file with a `poetry` section and a `project` section without a
+/// `dependencies` field, which should be treated as an empty list.
+#[test]
+fn compile_pyproject_toml_poetry_empty_dependencies() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[project]
+name = "poetry-editable"
+version = "0.1.0"
+description = ""
+authors = ["Astral Software Inc. <[email protected]>"]
+
+[tool.poetry]
+name = "poetry-editable"
+version = "0.1.0"
+description = ""
+authors = ["Astral Software Inc. <[email protected]>"]
+
+[tool.poetry.dependencies]
+python = "^3.10"
+anyio = "^3"
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
+"#,
+    )?;
+
+    uv_snapshot!(context.compile()
+            .arg("pyproject.toml"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] --exclude-newer 2024-03-25T00:00:00Z pyproject.toml
+    anyio==3.7.1
+        # via poetry-editable (pyproject.toml)
+    idna==3.6
+        # via anyio
+    sniffio==1.3.1
+        # via anyio
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
+/// Compile a `pyproject.toml` file with a `poetry` section and a `project` section with an invalid
+/// `dependencies` field.
+#[test]
+fn compile_pyproject_toml_poetry_invalid_dependencies() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"[project]
+name = "poetry-editable"
+version = "0.1.0"
+description = ""
+authors = ["Astral Software Inc. <[email protected]>"]
+
+[tool.poetry]
+name = "poetry-editable"
+version = "0.1.0"
+description = ""
+authors = ["Astral Software Inc. <[email protected]>"]
+
+[project.dependencies]
+python = "^3.12"
+msgspec = "^0.18.4"
+
+[tool.poetry.dependencies]
+python = "^3.10"
+anyio = "^3"
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
+"#,
+    )?;
+
+    uv_snapshot!(context.compile()
+            .arg("pyproject.toml"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to extract static metadata from `pyproject.toml`
+      Caused by: TOML parse error at line 13, column 1
+       |
+    13 | [project.dependencies]
+       | ^^^^^^^^^^^^^^^^^^^^^^
+    invalid type: map, expected a sequence
+
+    "###
+    );
+
+    Ok(())
+}
+
 /// Compile a `pyproject.toml` file that uses setuptools as the build backend.
 #[test]
 fn compile_pyproject_toml_setuptools() -> Result<()> {