Allow multiple source entries for each package in `tool.uv.sources` (#7745)

## Summary

This PR enables users to provide multiple source entries in
`tool.uv.sources`, e.g.:

```toml
[tool.uv.sources]
httpx = [
  { git = "https://github.com/encode/httpx", tag = "0.27.2", marker = "sys_platform == 'darwin'" },
  { git = "https://github.com/encode/httpx", tag = "0.24.1", marker = "sys_platform == 'linux'" },
]
```

The implementation is relatively straightforward: when we lower the
requirement, we now return an iterator rather than a single requirement.
In other words, the above is transformed into two requirements:

```txt
httpx @ git+https://github.com/encode/httpx@0.27.2 ; sys_platform == 'darwin'
httpx @ git+https://github.com/encode/httpx@0.24.1 ; sys_platform == 'linux'
```

We verify (at deserialization time) that the markers are
non-overlapping.

Closes https://github.com/astral-sh/uv/issues/3397.

Cargo.lock

@@ -4789,6 +4789,7 @@ dependencies = [
  "cache-key",
  "distribution-filename",
  "distribution-types",
+ "either",
  "fs-err",
  "futures",
  "indoc",
@@ -5319,6 +5320,7 @@ dependencies = [
  "glob",
  "insta",
  "itertools 0.13.0",
+ "owo-colors",
  "pep440_rs",
  "pep508_rs",
  "pypi-types",

crates/pep508-rs/src/marker/tree.rs

@@ -5,12 +5,11 @@ use std::ops::{Bound, Deref};
 use std::str::FromStr;
 
 use itertools::Itertools;
+use pep440_rs::{Version, VersionParseError, VersionSpecifier};
 use pubgrub::Range;
 #[cfg(feature = "pyo3")]
 use pyo3::{basic::CompareOp, pyclass, pymethods};
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
-
-use pep440_rs::{Version, VersionParseError, VersionSpecifier};
 use uv_normalize::ExtraName;
 
 use crate::cursor::Cursor;
@@ -1667,6 +1666,28 @@ impl Display for MarkerTreeContents {
     }
 }
 
+#[cfg(feature = "schemars")]
+impl schemars::JsonSchema for MarkerTree {
+    fn schema_name() -> String {
+        "MarkerTree".to_string()
+    }
+
+    fn json_schema(_gen: &mut schemars::gen::SchemaGenerator) -> schemars::schema::Schema {
+        schemars::schema::SchemaObject {
+            instance_type: Some(schemars::schema::InstanceType::String.into()),
+            metadata: Some(Box::new(schemars::schema::Metadata {
+                description: Some(
+                    "A PEP 508-compliant marker expression, e.g., `sys_platform == 'Darwin'`"
+                        .to_string(),
+                ),
+                ..schemars::schema::Metadata::default()
+            })),
+            ..schemars::schema::SchemaObject::default()
+        }
+        .into()
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::ops::Bound;

crates/uv-distribution/Cargo.toml

@@ -34,6 +34,7 @@ uv-warnings = { workspace = true }
 uv-workspace = { workspace = true }
 
 anyhow = { workspace = true }
+either = { workspace = true }
 fs-err = { workspace = true }
 futures = { workspace = true }
 nanoid = { workspace = true }

crates/uv-distribution/src/metadata/lowering.rs

@@ -1,18 +1,18 @@
+use either::Either;
 use std::collections::BTreeMap;
 use std::io;
 use std::path::{Path, PathBuf};
-
 use thiserror::Error;
 use url::Url;
 
 use distribution_filename::DistExtension;
 use pep440_rs::VersionSpecifiers;
-use pep508_rs::{VerbatimUrl, VersionOrUrl};
+use pep508_rs::{MarkerTree, VerbatimUrl, VersionOrUrl};
 use pypi_types::{ParsedUrlError, Requirement, RequirementSource, VerbatimParsedUrl};
 use uv_git::GitReference;
 use uv_normalize::PackageName;
 use uv_warnings::warn_user_once;
-use uv_workspace::pyproject::{PyProjectToml, Source};
+use uv_workspace::pyproject::{PyProjectToml, Source, Sources};
 use uv_workspace::Workspace;
 
 #[derive(Debug, Clone)]
@@ -28,13 +28,13 @@ enum Origin {
 
 impl LoweredRequirement {
     /// Combine `project.dependencies` or `project.optional-dependencies` with `tool.uv.sources`.
-    pub(crate) fn from_requirement(
+    pub(crate) fn from_requirement<'data>(
         requirement: pep508_rs::Requirement<VerbatimParsedUrl>,
-        project_name: &PackageName,
+        project_name: &'data PackageName,
-        project_dir: &Path,
+        project_dir: &'data Path,
-        project_sources: &BTreeMap<PackageName, Source>,
+        project_sources: &'data BTreeMap<PackageName, Sources>,
-        workspace: &Workspace,
+        workspace: &'data Workspace,
-    ) -> Result<Self, LoweringError> {
+    ) -> impl Iterator<Item = Result<LoweredRequirement, LoweringError>> + 'data {
         let (source, origin) = if let Some(source) = project_sources.get(&requirement.name) {
             (Some(source), Origin::Project)
         } else if let Some(source) = workspace.sources().get(&requirement.name) {
@@ -48,18 +48,16 @@ impl LoweredRequirement {
             // We require that when you use a package that's part of the workspace, ...
             !workspace.packages().contains_key(&requirement.name)
                 // ... it must be declared as a workspace dependency (`workspace = true`), ...
-                || matches!(
+                || source.as_ref().filter(|sources| !sources.is_empty()).is_some_and(|source| source.iter().all(|source| {
-                    source,
+                    matches!(source, Source::Workspace { workspace: true, .. })
-                    Some(Source::Workspace {
+                }))
-                        // By using toml, we technically support `workspace = false`.
-                        workspace: true
-                    })
-                )
                 // ... except for recursive self-inclusion (extras that activate other extras), e.g.
                 // `framework[machine_learning]` depends on `framework[cuda]`.
                 || &requirement.name == project_name;
         if !workspace_package_declared {
-            return Err(LoweringError::UndeclaredWorkspacePackage);
+            return Either::Left(std::iter::once(Err(
+                LoweringError::UndeclaredWorkspacePackage,
+            )));
         }
 
         let Some(source) = source else {
@@ -74,172 +72,282 @@ impl LoweredRequirement {
                     requirement.name
                 );
             }
-            return Ok(Self(Requirement::from(requirement)));
+            return Either::Left(std::iter::once(Ok(Self(Requirement::from(requirement)))));
         };
 
-        let source = match source {
+        // Determine whether the markers cover the full space for the requirement. If not, fill the
-            Source::Git {
+        // remaining space with the negation of the sources.
-                git,
+        let remaining = {
-                subdirectory,
+            // Determine the space covered by the sources.
-                rev,
+            let mut total = MarkerTree::FALSE;
-                tag,
+            for source in source.iter() {
-                branch,
+                total.or(source.marker());
-            } => {
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                git_source(&git, subdirectory.map(PathBuf::from), rev, tag, branch)?
             }
-            Source::Url { url, subdirectory } => {
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                url_source(url, subdirectory.map(PathBuf::from))?
-            }
-            Source::Path { path, editable } => {
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                path_source(
-                    PathBuf::from(path),
-                    origin,
-                    project_dir,
-                    workspace.install_path(),
-                    editable.unwrap_or(false),
-                )?
-            }
-            Source::Registry { index } => registry_source(&requirement, index)?,
-            Source::Workspace {
-                workspace: is_workspace,
-            } => {
-                if !is_workspace {
-                    return Err(LoweringError::WorkspaceFalse);
-                }
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                let member = workspace
-                    .packages()
-                    .get(&requirement.name)
-                    .ok_or(LoweringError::UndeclaredWorkspacePackage)?
-                    .clone();
 
-                // Say we have:
+            // Determine the space covered by the requirement.
-                // ```
+            let mut remaining = total.negate();
-                // root
+            remaining.and(requirement.marker.clone());
-                // ├── main_workspace  <- We want to the path from here ...
-                // │   ├── pyproject.toml
-                // │   └── uv.lock
-                // └──current_workspace
-                //    └── packages
-                //        └── current_package  <- ... to here.
-                //            └── pyproject.toml
-                // ```
-                // The path we need in the lockfile: `../current_workspace/packages/current_project`
-                // member root: `/root/current_workspace/packages/current_project`
-                // workspace install root: `/root/current_workspace`
-                // relative to workspace: `packages/current_project`
-                // workspace lock root: `../current_workspace`
-                // relative to main workspace: `../current_workspace/packages/current_project`
-                let url = VerbatimUrl::from_absolute_path(member.root())?;
-                let install_path = url.to_file_path().map_err(|()| {
-                    LoweringError::RelativeTo(io::Error::new(
-                        io::ErrorKind::Other,
-                        "Invalid path in file URL",
-                    ))
-                })?;
 
-                if member.pyproject_toml().is_package() {
+            LoweredRequirement(Requirement {
-                    RequirementSource::Directory {
+                marker: remaining,
-                        install_path,
+                ..Requirement::from(requirement.clone())
-                        url,
+            })
-                        editable: true,
-                        r#virtual: false,
-                    }
-                } else {
-                    RequirementSource::Directory {
-                        install_path,
-                        url,
-                        editable: false,
-                        r#virtual: true,
-                    }
-                }
-            }
-            Source::CatchAll { .. } => {
-                // Emit a dedicated error message, which is an improvement over Serde's default error.
-                return Err(LoweringError::InvalidEntry);
-            }
         };
-        Ok(Self(Requirement {
+
-            name: requirement.name,
+        Either::Right(
-            extras: requirement.extras,
+            source
-            marker: requirement.marker,
+                .into_iter()
-            source,
+                .map(move |source| {
-            origin: requirement.origin,
+                    let (source, mut marker) = match source {
-        }))
+                        Source::Git {
+                            git,
+                            subdirectory,
+                            rev,
+                            tag,
+                            branch,
+                            marker,
+                        } => {
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let source = git_source(
+                                &git,
+                                subdirectory.map(PathBuf::from),
+                                rev,
+                                tag,
+                                branch,
+                            )?;
+                            (source, marker)
+                        }
+                        Source::Url {
+                            url,
+                            subdirectory,
+                            marker,
+                        } => {
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let source = url_source(url, subdirectory.map(PathBuf::from))?;
+                            (source, marker)
+                        }
+                        Source::Path {
+                            path,
+                            editable,
+                            marker,
+                        } => {
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let source = path_source(
+                                PathBuf::from(path),
+                                origin,
+                                project_dir,
+                                workspace.install_path(),
+                                editable.unwrap_or(false),
+                            )?;
+                            (source, marker)
+                        }
+                        Source::Registry { index, marker } => {
+                            let source = registry_source(&requirement, index)?;
+                            (source, marker)
+                        }
+                        Source::Workspace {
+                            workspace: is_workspace,
+                            marker,
+                        } => {
+                            if !is_workspace {
+                                return Err(LoweringError::WorkspaceFalse);
+                            }
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let member = workspace
+                                .packages()
+                                .get(&requirement.name)
+                                .ok_or(LoweringError::UndeclaredWorkspacePackage)?
+                                .clone();
+
+                            // Say we have:
+                            // ```
+                            // root
+                            // ├── main_workspace  <- We want to the path from here ...
+                            // │   ├── pyproject.toml
+                            // │   └── uv.lock
+                            // └──current_workspace
+                            //    └── packages
+                            //        └── current_package  <- ... to here.
+                            //            └── pyproject.toml
+                            // ```
+                            // The path we need in the lockfile: `../current_workspace/packages/current_project`
+                            // member root: `/root/current_workspace/packages/current_project`
+                            // workspace install root: `/root/current_workspace`
+                            // relative to workspace: `packages/current_project`
+                            // workspace lock root: `../current_workspace`
+                            // relative to main workspace: `../current_workspace/packages/current_project`
+                            let url = VerbatimUrl::from_absolute_path(member.root())?;
+                            let install_path = url.to_file_path().map_err(|()| {
+                                LoweringError::RelativeTo(io::Error::new(
+                                    io::ErrorKind::Other,
+                                    "Invalid path in file URL",
+                                ))
+                            })?;
+
+                            let source = if member.pyproject_toml().is_package() {
+                                RequirementSource::Directory {
+                                    install_path,
+                                    url,
+                                    editable: true,
+                                    r#virtual: false,
+                                }
+                            } else {
+                                RequirementSource::Directory {
+                                    install_path,
+                                    url,
+                                    editable: false,
+                                    r#virtual: true,
+                                }
+                            };
+                            (source, marker)
+                        }
+                        Source::CatchAll { .. } => {
+                            // Emit a dedicated error message, which is an improvement over Serde's default error.
+                            return Err(LoweringError::InvalidEntry);
+                        }
+                    };
+
+                    marker.and(requirement.marker.clone());
+
+                    Ok(Self(Requirement {
+                        name: requirement.name.clone(),
+                        extras: requirement.extras.clone(),
+                        marker,
+                        source,
+                        origin: requirement.origin.clone(),
+                    }))
+                })
+                .chain(std::iter::once(Ok(remaining)))
+                .filter(|requirement| match requirement {
+                    Ok(requirement) => !requirement.0.marker.is_false(),
+                    Err(_) => true,
+                }),
+        )
     }
 
     /// Lower a [`pep508_rs::Requirement`] in a non-workspace setting (for example, in a PEP 723
     /// script, which runs in an isolated context).
-    pub fn from_non_workspace_requirement(
+    pub fn from_non_workspace_requirement<'data>(
         requirement: pep508_rs::Requirement<VerbatimParsedUrl>,
-        dir: &Path,
+        dir: &'data Path,
-        sources: &BTreeMap<PackageName, Source>,
+        sources: &'data BTreeMap<PackageName, Sources>,
-    ) -> Result<Self, LoweringError> {
+    ) -> impl Iterator<Item = Result<LoweredRequirement, LoweringError>> + 'data {
         let source = sources.get(&requirement.name).cloned();
 
         let Some(source) = source else {
-            return Ok(Self(Requirement::from(requirement)));
+            return Either::Left(std::iter::once(Ok(Self(Requirement::from(requirement)))));
         };
 
-        let source = match source {
+        // Determine whether the markers cover the full space for the requirement. If not, fill the
-            Source::Git {
+        // remaining space with the negation of the sources.
-                git,
+        let remaining = {
-                subdirectory,
+            // Determine the space covered by the sources.
-                rev,
+            let mut total = MarkerTree::FALSE;
-                tag,
+            for source in source.iter() {
-                branch,
+                total.or(source.marker());
-            } => {
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                git_source(&git, subdirectory.map(PathBuf::from), rev, tag, branch)?
-            }
-            Source::Url { url, subdirectory } => {
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                url_source(url, subdirectory.map(PathBuf::from))?
-            }
-            Source::Path { path, editable } => {
-                if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
-                    return Err(LoweringError::ConflictingUrls);
-                }
-                path_source(
-                    PathBuf::from(path),
-                    Origin::Project,
-                    dir,
-                    dir,
-                    editable.unwrap_or(false),
-                )?
-            }
-            Source::Registry { index } => registry_source(&requirement, index)?,
-            Source::Workspace { .. } => {
-                return Err(LoweringError::WorkspaceMember);
-            }
-            Source::CatchAll { .. } => {
-                // Emit a dedicated error message, which is an improvement over Serde's default
-                // error.
-                return Err(LoweringError::InvalidEntry);
             }
+
+            // Determine the space covered by the requirement.
+            let mut remaining = total.negate();
+            remaining.and(requirement.marker.clone());
+
+            LoweredRequirement(Requirement {
+                marker: remaining,
+                ..Requirement::from(requirement.clone())
+            })
         };
-        Ok(Self(Requirement {
+
-            name: requirement.name,
+        Either::Right(
-            extras: requirement.extras,
+            source
-            marker: requirement.marker,
+                .into_iter()
-            source,
+                .map(move |source| {
-            origin: requirement.origin,
+                    let (source, mut marker) = match source {
-        }))
+                        Source::Git {
+                            git,
+                            subdirectory,
+                            rev,
+                            tag,
+                            branch,
+                            marker,
+                        } => {
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let source = git_source(
+                                &git,
+                                subdirectory.map(PathBuf::from),
+                                rev,
+                                tag,
+                                branch,
+                            )?;
+                            (source, marker)
+                        }
+                        Source::Url {
+                            url,
+                            subdirectory,
+                            marker,
+                        } => {
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let source = url_source(url, subdirectory.map(PathBuf::from))?;
+                            (source, marker)
+                        }
+                        Source::Path {
+                            path,
+                            editable,
+                            marker,
+                        } => {
+                            if matches!(requirement.version_or_url, Some(VersionOrUrl::Url(_))) {
+                                return Err(LoweringError::ConflictingUrls);
+                            }
+                            let source = path_source(
+                                PathBuf::from(path),
+                                Origin::Project,
+                                dir,
+                                dir,
+                                editable.unwrap_or(false),
+                            )?;
+                            (source, marker)
+                        }
+                        Source::Registry { index, marker } => {
+                            let source = registry_source(&requirement, index)?;
+                            (source, marker)
+                        }
+                        Source::Workspace { .. } => {
+                            return Err(LoweringError::WorkspaceMember);
+                        }
+                        Source::CatchAll { .. } => {
+                            // Emit a dedicated error message, which is an improvement over Serde's default
+                            // error.
+                            return Err(LoweringError::InvalidEntry);
+                        }
+                    };
+
+                    marker.and(requirement.marker.clone());
+
+                    Ok(Self(Requirement {
+                        name: requirement.name.clone(),
+                        extras: requirement.extras.clone(),
+                        marker,
+                        source,
+                        origin: requirement.origin.clone(),
+                    }))
+                })
+                .chain(std::iter::once(Ok(remaining)))
+                .filter(|requirement| match requirement {
+                    Ok(requirement) => !requirement.0.marker.is_false(),
+                    Err(_) => true,
+                }),
+        )
     }
 
     /// Convert back into a [`Requirement`].

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

@@ -22,6 +22,8 @@ pub enum MetadataError {
     Workspace(#[from] WorkspaceError),
     #[error("Failed to parse entry for: `{0}`")]
     LoweringError(PackageName, #[source] LoweringError),
+    #[error(transparent)]
+    Lower(#[from] LoweringError),
 }
 
 #[derive(Debug, Clone)]

crates/uv-distribution/src/metadata/requires_dist.rs

@@ -1,6 +1,6 @@
 use crate::metadata::{LoweredRequirement, MetadataError};
 use crate::Metadata;
-use pypi_types::Requirement;
+
 use std::collections::BTreeMap;
 use std::path::Path;
 use uv_configuration::SourceStrategy;
@@ -84,7 +84,7 @@ impl RequiresDist {
                 .cloned();
             let dev_dependencies = match source_strategy {
                 SourceStrategy::Enabled => dev_dependencies
-                    .map(|requirement| {
+                    .flat_map(|requirement| {
                         let requirement_name = requirement.name.clone();
                         LoweredRequirement::from_requirement(
                             requirement,
@@ -93,13 +93,17 @@ impl RequiresDist {
                             sources,
                             project_workspace.workspace(),
                         )
-                        .map(LoweredRequirement::into_inner)
+                        .map(move |requirement| match requirement {
-                        .map_err(|err| MetadataError::LoweringError(requirement_name.clone(), err))
+                            Ok(requirement) => Ok(requirement.into_inner()),
+                            Err(err) => {
+                                Err(MetadataError::LoweringError(requirement_name.clone(), err))
+                            }
+                        })
                     })
                     .collect::<Result<Vec<_>, _>>()?,
                 SourceStrategy::Disabled => dev_dependencies
                     .into_iter()
-                    .map(Requirement::from)
+                    .map(pypi_types::Requirement::from)
                     .collect(),
             };
             if dev_dependencies.is_empty() {
@@ -112,7 +116,7 @@ impl RequiresDist {
         let requires_dist = metadata.requires_dist.into_iter();
         let requires_dist = match source_strategy {
             SourceStrategy::Enabled => requires_dist
-                .map(|requirement| {
+                .flat_map(|requirement| {
                     let requirement_name = requirement.name.clone();
                     LoweredRequirement::from_requirement(
                         requirement,
@@ -121,11 +125,18 @@ impl RequiresDist {
                         sources,
                         project_workspace.workspace(),
                     )
-                    .map(LoweredRequirement::into_inner)
+                    .map(move |requirement| match requirement {
-                    .map_err(|err| MetadataError::LoweringError(requirement_name.clone(), err))
+                        Ok(requirement) => Ok(requirement.into_inner()),
+                        Err(err) => {
+                            Err(MetadataError::LoweringError(requirement_name.clone(), err))
+                        }
+                    })
                 })
-                .collect::<Result<_, _>>()?,
+                .collect::<Result<Vec<_>, _>>()?,
-            SourceStrategy::Disabled => requires_dist.into_iter().map(Requirement::from).collect(),
+            SourceStrategy::Disabled => requires_dist
+                .into_iter()
+                .map(pypi_types::Requirement::from)
+                .collect(),
         };
 
         Ok(Self {
@@ -253,7 +264,7 @@ mod test {
           |
         8 | tqdm = { git = "https://github.com/tqdm/tqdm", ref = "baaaaaab" }
           |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-        data did not match any variant of untagged enum Source
+        data did not match any variant of untagged enum SourcesWire
 
         "###);
     }
@@ -277,7 +288,7 @@ mod test {
           |
         8 | tqdm = { path = "tqdm", index = "torch" }
           |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-        data did not match any variant of untagged enum Source
+        data did not match any variant of untagged enum SourcesWire
 
         "###);
     }
@@ -337,7 +348,7 @@ mod test {
           |
         8 | tqdm = { url = "§invalid#+#*Ä" }
           |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^
-        data did not match any variant of untagged enum Source
+        data did not match any variant of untagged enum SourcesWire
 
         "###);
     }

crates/uv-scripts/src/lib.rs

@@ -12,7 +12,7 @@ use pep440_rs::VersionSpecifiers;
 use pep508_rs::PackageName;
 use pypi_types::VerbatimParsedUrl;
 use uv_settings::{GlobalOptions, ResolverInstallerOptions};
-use uv_workspace::pyproject::Source;
+use uv_workspace::pyproject::Sources;
 
 static FINDER: LazyLock<Finder> = LazyLock::new(|| Finder::new(b"# /// script"));
 
@@ -193,7 +193,7 @@ pub struct ToolUv {
     pub globals: GlobalOptions,
     #[serde(flatten)]
     pub top_level: ResolverInstallerOptions,
-    pub sources: Option<BTreeMap<PackageName, Source>>,
+    pub sources: Option<BTreeMap<PackageName, Sources>>,
 }
 
 #[derive(Debug, Error)]

crates/uv-workspace/Cargo.toml

@@ -26,6 +26,8 @@ uv-options-metadata = { workspace = true }
 either = { workspace = true }
 fs-err = { workspace = true }
 glob = { workspace = true }
+itertools = { workspace = true }
+owo-colors = { workspace = true }
 rustc-hash = { workspace = true }
 same-file = { workspace = true }
 schemars = { workspace = true, optional = true }
@@ -36,7 +38,6 @@ toml =  { workspace = true }
 toml_edit =  { workspace = true }
 tracing = { workspace = true }
 url = { workspace = true }
-itertools = { workspace = true }
 
 [dev-dependencies]
 anyhow = { workspace = true }

crates/uv-workspace/src/pyproject.rs

@@ -7,6 +7,7 @@
 //! Then lowers them into a dependency specification.
 
 use glob::Pattern;
+use owo_colors::OwoColorize;
 use serde::{de::IntoDeserializer, Deserialize, Serialize};
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
@@ -16,6 +17,7 @@ use thiserror::Error;
 use url::Url;
 
 use pep440_rs::{Version, VersionSpecifiers};
+use pep508_rs::MarkerTree;
 use pypi_types::{RequirementSource, SupportedEnvironments, VerbatimParsedUrl};
 use uv_fs::{relative_to, PortablePathBuf};
 use uv_git::GitReference;
@@ -294,17 +296,17 @@ pub struct ToolUv {
 #[derive(Default, Debug, Clone, PartialEq, Eq)]
 #[cfg_attr(test, derive(Serialize))]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
-pub struct ToolUvSources(BTreeMap<PackageName, Source>);
+pub struct ToolUvSources(BTreeMap<PackageName, Sources>);
 
 impl ToolUvSources {
     /// Returns the underlying `BTreeMap` of package names to sources.
-    pub fn inner(&self) -> &BTreeMap<PackageName, Source> {
+    pub fn inner(&self) -> &BTreeMap<PackageName, Sources> {
         &self.0
     }
 
     /// Convert the [`ToolUvSources`] into its inner `BTreeMap`.
     #[must_use]
-    pub fn into_inner(self) -> BTreeMap<PackageName, Source> {
+    pub fn into_inner(self) -> BTreeMap<PackageName, Sources> {
         self.0
     }
 }
@@ -329,7 +331,7 @@ impl<'de> serde::de::Deserialize<'de> for ToolUvSources {
                 M: serde::de::MapAccess<'de>,
             {
                 let mut sources = BTreeMap::new();
-                while let Some((key, value)) = access.next_entry::<PackageName, Source>()? {
+                while let Some((key, value)) = access.next_entry::<PackageName, Sources>()? {
                     match sources.entry(key) {
                         std::collections::btree_map::Entry::Occupied(entry) => {
                             return Err(serde::de::Error::custom(format!(
@@ -407,6 +409,105 @@ impl Deref for SerdePattern {
     }
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+#[serde(rename_all = "kebab-case", try_from = "SourcesWire")]
+pub struct Sources(#[cfg_attr(feature = "schemars", schemars(with = "SourcesWire"))] Vec<Source>);
+
+impl Sources {
+    /// Return an [`Iterator`] over the sources.
+    ///
+    /// If the iterator contains multiple entries, they will always use disjoint markers.
+    ///
+    /// The iterator will contain at most one registry source.
+    pub fn iter(&self) -> impl Iterator<Item = &Source> {
+        self.0.iter()
+    }
+
+    /// Returns `true` if the sources list is empty.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    /// Returns the number of sources in the list.
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
+impl IntoIterator for Sources {
+    type Item = Source;
+    type IntoIter = std::vec::IntoIter<Source>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
+#[serde(rename_all = "kebab-case", untagged)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+#[allow(clippy::large_enum_variant)]
+enum SourcesWire {
+    One(Source),
+    Many(Vec<Source>),
+}
+
+impl TryFrom<SourcesWire> for Sources {
+    type Error = SourceError;
+
+    fn try_from(wire: SourcesWire) -> Result<Self, Self::Error> {
+        match wire {
+            SourcesWire::One(source) => Ok(Self(vec![source])),
+            SourcesWire::Many(sources) => {
+                // Ensure that the markers are disjoint.
+                for (lhs, rhs) in sources
+                    .iter()
+                    .map(Source::marker)
+                    .zip(sources.iter().skip(1).map(Source::marker))
+                {
+                    if !lhs.is_disjoint(&rhs) {
+                        let mut hint = lhs.negate();
+                        hint.and(rhs.clone());
+
+                        let lhs = lhs
+                            .contents()
+                            .map(|contents| contents.to_string())
+                            .unwrap_or_else(|| "true".to_string());
+                        let rhs = rhs
+                            .contents()
+                            .map(|contents| contents.to_string())
+                            .unwrap_or_else(|| "true".to_string());
+                        let hint = hint
+                            .contents()
+                            .map(|contents| contents.to_string())
+                            .unwrap_or_else(|| "true".to_string());
+
+                        return Err(SourceError::OverlappingMarkers(lhs, rhs, hint));
+                    }
+                }
+
+                // Ensure that there is at least one source.
+                if sources.is_empty() {
+                    return Err(SourceError::EmptySources);
+                }
+
+                // Ensure that there is at most one registry source.
+                if sources
+                    .iter()
+                    .filter(|source| matches!(source, Source::Registry { .. }))
+                    .nth(1)
+                    .is_some()
+                {
+                    return Err(SourceError::MultipleIndexes);
+                }
+
+                Ok(Self(sources))
+            }
+        }
+    }
+}
+
 /// A `tool.uv.sources` value.
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
@@ -427,6 +528,12 @@ pub enum Source {
         rev: Option<String>,
         tag: Option<String>,
         branch: Option<String>,
+        #[serde(
+            skip_serializing_if = "pep508_rs::marker::ser::is_empty",
+            serialize_with = "pep508_rs::marker::ser::serialize",
+            default
+        )]
+        marker: MarkerTree,
     },
     /// A remote `http://` or `https://` URL, either a wheel (`.whl`) or a source distribution
     /// (`.zip`, `.tar.gz`).
@@ -440,6 +547,12 @@ pub enum Source {
         /// For source distributions, the path to the directory with the `pyproject.toml`, if it's
         /// not in the archive root.
         subdirectory: Option<PortablePathBuf>,
+        #[serde(
+            skip_serializing_if = "pep508_rs::marker::ser::is_empty",
+            serialize_with = "pep508_rs::marker::ser::serialize",
+            default
+        )]
+        marker: MarkerTree,
     },
     /// The path to a dependency, either a wheel (a `.whl` file), source distribution (a `.zip` or
     /// `.tar.gz` file), or source tree (i.e., a directory containing a `pyproject.toml` or
@@ -448,17 +561,35 @@ pub enum Source {
         path: PortablePathBuf,
         /// `false` by default.
         editable: Option<bool>,
+        #[serde(
+            skip_serializing_if = "pep508_rs::marker::ser::is_empty",
+            serialize_with = "pep508_rs::marker::ser::serialize",
+            default
+        )]
+        marker: MarkerTree,
     },
     /// A dependency pinned to a specific index, e.g., `torch` after setting `torch` to `https://download.pytorch.org/whl/cu118`.
     Registry {
         // TODO(konstin): The string is more-or-less a placeholder
         index: String,
+        #[serde(
+            skip_serializing_if = "pep508_rs::marker::ser::is_empty",
+            serialize_with = "pep508_rs::marker::ser::serialize",
+            default
+        )]
+        marker: MarkerTree,
     },
     /// A dependency on another package in the workspace.
     Workspace {
         /// When set to `false`, the package will be fetched from the remote index, rather than
         /// included as a workspace package.
         workspace: bool,
+        #[serde(
+            skip_serializing_if = "pep508_rs::marker::ser::is_empty",
+            serialize_with = "pep508_rs::marker::ser::serialize",
+            default
+        )]
+        marker: MarkerTree,
     },
     /// A catch-all variant used to emit precise error messages when deserializing.
     CatchAll {
@@ -471,6 +602,12 @@ pub enum Source {
         path: PortablePathBuf,
         index: String,
         workspace: bool,
+        #[serde(
+            skip_serializing_if = "pep508_rs::marker::ser::is_empty",
+            serialize_with = "pep508_rs::marker::ser::serialize",
+            default
+        )]
+        marker: MarkerTree,
     },
 }
 
@@ -494,6 +631,12 @@ pub enum SourceError {
     Absolute(#[from] std::io::Error),
     #[error("Path contains invalid characters: `{}`", _0.display())]
     NonUtf8Path(PathBuf),
+    #[error("Source markers must be disjoint, but the following markers overlap: `{0}` and `{1}`.\n\n{hint}{colon} replace `{1}` with `{2}`.", hint = "hint".bold().cyan(), colon = ":".bold())]
+    OverlappingMarkers(String, String, String),
+    #[error("Must provide at least one source")]
+    EmptySources,
+    #[error("Sources can only include a single index source")]
+    MultipleIndexes,
 }
 
 impl Source {
@@ -524,7 +667,10 @@ impl Source {
         if workspace {
             return match source {
                 RequirementSource::Registry { .. } | RequirementSource::Directory { .. } => {
-                    Ok(Some(Source::Workspace { workspace: true }))
+                    Ok(Some(Source::Workspace {
+                        workspace: true,
+                        marker: MarkerTree::TRUE,
+                    }))
                 }
                 RequirementSource::Url { .. } => {
                     Err(SourceError::WorkspacePackageUrl(name.to_string()))
@@ -548,12 +694,14 @@ impl Source {
                         .or_else(|_| std::path::absolute(&install_path))
                         .map_err(SourceError::Absolute)?,
                 ),
+                marker: MarkerTree::TRUE,
             },
             RequirementSource::Url {
                 subdirectory, url, ..
             } => Source::Url {
                 url: url.to_url(),
                 subdirectory: subdirectory.map(PortablePathBuf::from),
+                marker: MarkerTree::TRUE,
             },
             RequirementSource::Git {
                 repository,
@@ -578,6 +726,7 @@ impl Source {
                         branch,
                         git: repository,
                         subdirectory: subdirectory.map(PortablePathBuf::from),
+                        marker: MarkerTree::TRUE,
                     }
                 } else {
                     Source::Git {
@@ -586,6 +735,7 @@ impl Source {
                         branch,
                         git: repository,
                         subdirectory: subdirectory.map(PortablePathBuf::from),
+                        marker: MarkerTree::TRUE,
                     }
                 }
             }
@@ -593,6 +743,18 @@ impl Source {
 
         Ok(Some(source))
     }
+
+    /// Return the [`MarkerTree`] for the source.
+    pub fn marker(&self) -> MarkerTree {
+        match self {
+            Source::Git { marker, .. } => marker.clone(),
+            Source::Url { marker, .. } => marker.clone(),
+            Source::Path { marker, .. } => marker.clone(),
+            Source::Registry { marker, .. } => marker.clone(),
+            Source::Workspace { marker, .. } => marker.clone(),
+            Source::CatchAll { marker, .. } => marker.clone(),
+        }
+    }
 }
 
 /// The type of a dependency in a `pyproject.toml`.

crates/uv-workspace/src/workspace.rs

@@ -14,7 +14,7 @@ use uv_normalize::{GroupName, PackageName, DEV_DEPENDENCIES};
 use uv_warnings::{warn_user, warn_user_once};
 
 use crate::pyproject::{
-    Project, PyProjectToml, PyprojectTomlError, Source, ToolUvSources, ToolUvWorkspace,
+    Project, PyProjectToml, PyprojectTomlError, Source, Sources, ToolUvSources, ToolUvWorkspace,
 };
 
 #[derive(thiserror::Error, Debug)]
@@ -78,7 +78,7 @@ pub struct Workspace {
     /// The sources table from the workspace `pyproject.toml`.
     ///
     /// This table is overridden by the project sources.
-    sources: BTreeMap<PackageName, Source>,
+    sources: BTreeMap<PackageName, Sources>,
     /// The `pyproject.toml` of the workspace root.
     pyproject_toml: PyProjectToml,
 }
@@ -517,7 +517,7 @@ impl Workspace {
     }
 
     /// The sources table from the workspace `pyproject.toml`.
-    pub fn sources(&self) -> &BTreeMap<PackageName, Source> {
+    pub fn sources(&self) -> &BTreeMap<PackageName, Sources> {
         &self.sources
     }
 
@@ -531,7 +531,7 @@ impl Workspace {
                         .as_ref()
                         .and_then(|uv| uv.sources.as_ref())
                         .map(ToolUvSources::inner)
-                        .map(|sources| sources.values())
+                        .map(|sources| sources.values().flat_map(Sources::iter))
                 })
             })
             .flatten()
@@ -1755,9 +1755,11 @@ mod tests {
                   }
                 },
                 "sources": {
-                  "bird-feeder": {
+                  "bird-feeder": [
-                    "workspace": true
+                    {
-                  }
+                      "workspace": true
+                    }
+                  ]
                 },
                 "pyproject_toml": {
                   "project": {
@@ -1773,9 +1775,11 @@ mod tests {
                   "tool": {
                     "uv": {
                       "sources": {
-                        "bird-feeder": {
+                        "bird-feeder": [
-                          "workspace": true
+                          {
-                        }
+                            "workspace": true
+                          }
+                        ]
                       },
                       "workspace": {
                         "members": [

crates/uv/src/commands/project/add.rs

@@ -453,6 +453,7 @@ pub(crate) async fn add(
                 rev,
                 tag,
                 branch,
+                marker,
             }) => {
                 let credentials = Credentials::from_url(&git);
                 if let Some(credentials) = credentials {
@@ -468,6 +469,7 @@ pub(crate) async fn add(
                     rev,
                     tag,
                     branch,
+                    marker,
                 })
             }
             _ => source,

crates/uv/src/commands/project/lock.rs

@@ -293,15 +293,15 @@ async fn do_lock(
                     let lhs = lhs
                         .contents()
                         .map(|contents| contents.to_string())
-                        .unwrap_or("true".to_string());
+                        .unwrap_or_else(|| "true".to_string());
                     let rhs = rhs
                         .contents()
                         .map(|contents| contents.to_string())
-                        .unwrap_or("true".to_string());
+                        .unwrap_or_else(|| "true".to_string());
                     let hint = hint
                         .contents()
                         .map(|contents| contents.to_string())
-                        .unwrap_or("true".to_string());
+                        .unwrap_or_else(|| "true".to_string());
 
                     return Err(ProjectError::OverlappingMarkers(lhs, rhs, hint));
                 }

crates/uv/src/commands/project/run.rs

@@ -196,13 +196,13 @@ pub(crate) async fn run(
 
             let requirements = dependencies
                 .into_iter()
-                .map(|requirement| {
+                .flat_map(|requirement| {
                     LoweredRequirement::from_non_workspace_requirement(
                         requirement,
                         script_dir,
                         script_sources,
                     )
-                    .map(LoweredRequirement::into_inner)
+                    .map_ok(uv_distribution::LoweredRequirement::into_inner)
                 })
                 .collect::<Result<_, _>>()?;
             let spec = RequirementsSpecification::from_requirements(requirements);

crates/uv/src/commands/project/sync.rs

@@ -28,7 +28,7 @@ use uv_python::{PythonDownloads, PythonEnvironment, PythonPreference, PythonRequ
 use uv_resolver::{FlatIndex, Lock};
 use uv_types::{BuildIsolation, HashStrategy};
 use uv_warnings::warn_user;
-use uv_workspace::pyproject::{Source, ToolUvSources};
+use uv_workspace::pyproject::{Source, Sources, ToolUvSources};
 use uv_workspace::{DiscoveryOptions, InstallTarget, MemberDiscovery, VirtualProject, Workspace};
 
 /// Sync the project environment.
@@ -425,7 +425,7 @@ fn store_credentials_from_workspace(workspace: &Workspace) {
             .and_then(|uv| uv.sources.as_ref())
             .map(ToolUvSources::inner)
             .iter()
-            .flat_map(|sources| sources.values())
+            .flat_map(|sources| sources.values().flat_map(Sources::iter))
         {
             match source {
                 Source::Git { git, .. } => {

crates/uv/tests/lock.rs

@@ -13323,3 +13323,468 @@ fn lock_change_requires_python() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn lock_multiple_sources() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+
+        [tool.uv.sources]
+        iniconfig = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", marker = "sys_platform != 'win32'" },
+            { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz", marker = "sys_platform == 'win32'" },
+        ]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            lock, @r###"
+        version = 1
+        requires-python = ">=3.12"
+        resolution-markers = [
+            "sys_platform != 'win32'",
+            "sys_platform == 'win32'",
+        ]
+
+        [options]
+        exclude-newer = "2024-03-25T00:00:00Z"
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz" }
+        resolution-markers = [
+            "sys_platform == 'win32'",
+        ]
+        sdist = { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz", hash = "sha256:2d91e135bf72d31a410b17c16da610a82cb55f6b0477d1a902134b24a455b8b3" }
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }
+        resolution-markers = [
+            "sys_platform != 'win32'",
+        ]
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374" },
+        ]
+
+        [[package]]
+        name = "project"
+        version = "0.1.0"
+        source = { virtual = "." }
+        dependencies = [
+            { name = "iniconfig", version = "2.0.0", source = { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz" }, marker = "sys_platform == 'win32'" },
+            { name = "iniconfig", version = "2.0.0", source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }, marker = "sys_platform != 'win32'" },
+        ]
+
+        [package.metadata]
+        requires-dist = [
+            { name = "iniconfig", marker = "sys_platform != 'win32'", url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" },
+            { name = "iniconfig", marker = "sys_platform == 'win32'", url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz" },
+        ]
+        "###
+        );
+    });
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    Ok(())
+}
+
+#[test]
+fn lock_multiple_sources_conflict() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+
+        [tool.uv.sources]
+        iniconfig = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", marker = "sys_platform == 'win32' and python_version == '3.12'" },
+            { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz", marker = "sys_platform == 'win32'" },
+        ]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to parse: `pyproject.toml`
+      Caused by: TOML parse error at line 9, column 21
+      |
+    9 |         iniconfig = [
+      |                     ^
+    Source markers must be disjoint, but the following markers overlap: `python_full_version == '3.12.*' and sys_platform == 'win32'` and `sys_platform == 'win32'`.
+
+    hint: replace `sys_platform == 'win32'` with `python_full_version != '3.12.*' and sys_platform == 'win32'`.
+
+    "###);
+
+    Ok(())
+}
+
+/// Multiple `index` entries is not yet supported.
+#[test]
+fn lock_multiple_sources_index() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+
+        [tool.uv.sources]
+        iniconfig = [
+            { index = "pytorch", marker = "sys_platform != 'win32'" },
+            { index = "internal", marker = "sys_platform == 'win32'" },
+        ]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to parse: `pyproject.toml`
+      Caused by: TOML parse error at line 9, column 21
+      |
+    9 |         iniconfig = [
+      |                     ^
+    Sources can only include a single index source
+
+    "###);
+
+    Ok(())
+}
+
+#[test]
+fn lock_multiple_sources_non_total() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+
+        [tool.uv.sources]
+        iniconfig = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", marker = "sys_platform == 'darwin'" },
+        ]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            lock, @r###"
+        version = 1
+        requires-python = ">=3.12"
+        resolution-markers = [
+            "sys_platform == 'darwin'",
+            "sys_platform != 'darwin'",
+        ]
+
+        [options]
+        exclude-newer = "2024-03-25T00:00:00Z"
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { registry = "https://pypi.org/simple" }
+        resolution-markers = [
+            "sys_platform != 'darwin'",
+        ]
+        sdist = { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz", hash = "sha256:2d91e135bf72d31a410b17c16da610a82cb55f6b0477d1a902134b24a455b8b3", size = 4646 }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374", size = 5892 },
+        ]
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }
+        resolution-markers = [
+            "sys_platform == 'darwin'",
+        ]
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374" },
+        ]
+
+        [[package]]
+        name = "project"
+        version = "0.1.0"
+        source = { virtual = "." }
+        dependencies = [
+            { name = "iniconfig", version = "2.0.0", source = { registry = "https://pypi.org/simple" }, marker = "sys_platform != 'darwin'" },
+            { name = "iniconfig", version = "2.0.0", source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }, marker = "sys_platform == 'darwin'" },
+        ]
+
+        [package.metadata]
+        requires-dist = [
+            { name = "iniconfig", marker = "sys_platform != 'darwin'" },
+            { name = "iniconfig", marker = "sys_platform == 'darwin'", url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" },
+        ]
+        "###
+        );
+    });
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    Ok(())
+}
+
+#[test]
+fn lock_multiple_sources_respect_marker() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig ; platform_system == 'Windows'"]
+
+        [tool.uv.sources]
+        iniconfig = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", marker = "sys_platform == 'darwin'" },
+        ]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            lock, @r###"
+        version = 1
+        requires-python = ">=3.12"
+        resolution-markers = [
+            "platform_system == 'Windows' and sys_platform == 'darwin'",
+            "platform_system == 'Windows' and sys_platform != 'darwin'",
+            "platform_system != 'Windows'",
+        ]
+
+        [options]
+        exclude-newer = "2024-03-25T00:00:00Z"
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { registry = "https://pypi.org/simple" }
+        resolution-markers = [
+            "platform_system == 'Windows' and sys_platform != 'darwin'",
+        ]
+        sdist = { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz", hash = "sha256:2d91e135bf72d31a410b17c16da610a82cb55f6b0477d1a902134b24a455b8b3", size = 4646 }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374", size = 5892 },
+        ]
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }
+        resolution-markers = [
+            "platform_system == 'Windows' and sys_platform == 'darwin'",
+        ]
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374" },
+        ]
+
+        [[package]]
+        name = "project"
+        version = "0.1.0"
+        source = { virtual = "." }
+        dependencies = [
+            { name = "iniconfig", version = "2.0.0", source = { registry = "https://pypi.org/simple" }, marker = "platform_system == 'Windows' and sys_platform != 'darwin'" },
+            { name = "iniconfig", version = "2.0.0", source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }, marker = "platform_system == 'Windows' and sys_platform == 'darwin'" },
+        ]
+
+        [package.metadata]
+        requires-dist = [
+            { name = "iniconfig", marker = "platform_system == 'Windows' and sys_platform != 'darwin'" },
+            { name = "iniconfig", marker = "platform_system == 'Windows' and sys_platform == 'darwin'", url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" },
+        ]
+        "###
+        );
+    });
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    "###);
+
+    Ok(())
+}
+
+#[test]
+fn lock_multiple_sources_extra() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+
+        [project.optional-dependencies]
+        cpu = []
+
+        [tool.uv.sources]
+        iniconfig = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", marker = "extra == 'cpu'" },
+        ]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    "###);
+
+    let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            lock, @r###"
+        version = 1
+        requires-python = ">=3.12"
+
+        [options]
+        exclude-newer = "2024-03-25T00:00:00Z"
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374" },
+        ]
+
+        [[package]]
+        name = "project"
+        version = "0.1.0"
+        source = { virtual = "." }
+
+        [package.optional-dependencies]
+        cpu = [
+            { name = "iniconfig" },
+        ]
+
+        [package.metadata]
+        requires-dist = [
+            { name = "iniconfig", marker = "extra == 'cpu'", url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" },
+            { name = "iniconfig", marker = "extra != 'cpu'" },
+        ]
+        "###
+        );
+    });
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    "###);
+
+    Ok(())
+}

docs/concepts/dependencies.md

@@ -223,6 +223,46 @@ members = [
 ]
 ```
 
+### Platform-specific sources
+
+You can limit a source to a given platform or Python version by providing
+[PEP 508](https://peps.python.org/pep-0508/#environment-markers)-compatible environment markers for
+the source.
+
+For example, to pull `httpx` from GitHub, but only on macOS, use the following:
+
+```toml title="pyproject.toml"
+[project]
+dependencies = [
+  "httpx",
+]
+
+[tool.uv.sources]
+httpx = { git = "https://github.com/encode/httpx", tag = "0.27.2", marker = "sys_platform == 'darwin'" }
+```
+
+By specifying the marker on the source, uv will still include `httpx` on all platforms, but will
+download the source from GitHub on macOS, and fall back to PyPI on all other platforms.
+
+### Multiple sources
+
+You can specify multiple sources for a single dependency by providing a list of sources,
+disambiguated by [PEP 508](https://peps.python.org/pep-0508/#environment-markers)-compatible
+environment markers. For example, to pull in different `httpx` commits on macOS vs. Linux:
+
+```toml title="pyproject.toml"
+[project]
+dependencies = [
+  "httpx",
+]
+
+[tool.uv.sources]
+httpx = [
+  { git = "https://github.com/encode/httpx", tag = "0.27.2", marker = "sys_platform == 'darwin'" },
+  { git = "https://github.com/encode/httpx", tag = "0.24.1", marker = "sys_platform == 'linux'" },
+]
+```
+
 ## Optional dependencies
 
 It is common for projects that are published as libraries to make some features optional to reduce

uv.schema.json

@@ -625,6 +625,10 @@
         }
       ]
     },
+    "MarkerTree": {
+      "description": "A PEP 508-compliant marker expression, e.g., `sys_platform == 'Darwin'`",
+      "type": "string"
+    },
     "PackageName": {
       "description": "The normalized name of a package.\n\nConverts the name to lowercase and collapses runs of `-`, `_`, and `.` down to a single `-`. For example, `---`, `.`, and `__` are all converted to a single `-`.\n\nSee: <https://packaging.python.org/en/latest/specifications/name-normalization/>",
       "type": "string"
@@ -1240,6 +1244,9 @@
               "type": "string",
               "format": "uri"
             },
+            "marker": {
+              "$ref": "#/definitions/MarkerTree"
+            },
             "rev": {
               "type": [
                 "string",
@@ -1273,6 +1280,9 @@
             "url"
           ],
           "properties": {
+            "marker": {
+              "$ref": "#/definitions/MarkerTree"
+            },
             "subdirectory": {
               "description": "For source distributions, the path to the directory with the `pyproject.toml`, if it's not in the archive root.",
               "anyOf": [
@@ -1305,6 +1315,9 @@
                 "null"
               ]
             },
+            "marker": {
+              "$ref": "#/definitions/MarkerTree"
+            },
             "path": {
               "$ref": "#/definitions/String"
             }
@@ -1320,6 +1333,9 @@
           "properties": {
             "index": {
               "type": "string"
+            },
+            "marker": {
+              "$ref": "#/definitions/MarkerTree"
             }
           },
           "additionalProperties": false
@@ -1331,6 +1347,9 @@
             "workspace"
           ],
           "properties": {
+            "marker": {
+              "$ref": "#/definitions/MarkerTree"
+            },
             "workspace": {
               "description": "When set to `false`, the package will be fetched from the remote index, rather than included as a workspace package.",
               "type": "boolean"
@@ -1361,6 +1380,9 @@
             "index": {
               "type": "string"
             },
+            "marker": {
+              "$ref": "#/definitions/MarkerTree"
+            },
             "path": {
               "$ref": "#/definitions/String"
             },
@@ -1397,6 +1419,22 @@
         }
       ]
     },
+    "Sources": {
+      "$ref": "#/definitions/SourcesWire"
+    },
+    "SourcesWire": {
+      "anyOf": [
+        {
+          "$ref": "#/definitions/Source"
+        },
+        {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/Source"
+          }
+        }
+      ]
+    },
     "StaticMetadata": {
       "description": "A subset of the Python Package Metadata 2.3 standard as specified in <https://packaging.python.org/specifications/core-metadata/>.",
       "type": "object",
@@ -1565,7 +1603,7 @@
     "ToolUvSources": {
       "type": "object",
       "additionalProperties": {
-        "$ref": "#/definitions/Source"
+        "$ref": "#/definitions/Sources"
       }
     },
     "ToolUvWorkspace": {