Add --package to uv sync (#5656)

## Summary

Closes https://github.com/astral-sh/uv/issues/5008.

crates/uv-cli/src/lib.rs

@@ -2008,6 +2008,10 @@ pub struct SyncArgs {
     #[command(flatten)]
     pub refresh: RefreshArgs,
 
+    /// Sync a specific package in the workspace.
+    #[arg(long)]
+    pub package: Option<PackageName>,
+
     /// The Python interpreter to use to build the run environment.
     ///
     /// By default, uv uses the virtual environment in the current working directory or any parent

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

@@ -1,4 +1,4 @@
-use anyhow::Result;
+use anyhow::{Context, Result};
 
 use uv_auth::store_credentials_from_url;
 use uv_cache::Cache;
@@ -10,11 +10,12 @@ use uv_dispatch::BuildDispatch;
 use uv_distribution::DEV_DEPENDENCIES;
 use uv_fs::CWD;
 use uv_installer::SitePackages;
+use uv_normalize::PackageName;
 use uv_python::{PythonEnvironment, PythonFetch, PythonPreference, PythonRequest};
 use uv_resolver::{FlatIndex, Lock};
 use uv_types::{BuildIsolation, HashStrategy};
 use uv_warnings::warn_user_once;
-use uv_workspace::{DiscoveryOptions, VirtualProject};
+use uv_workspace::{DiscoveryOptions, VirtualProject, Workspace};
 
 use crate::commands::pip::operations::Modifications;
 use crate::commands::project::lock::do_safe_lock;
@@ -28,6 +29,7 @@ use crate::settings::{InstallerSettingsRef, ResolverInstallerSettings};
 pub(crate) async fn sync(
     locked: bool,
     frozen: bool,
+    package: Option<PackageName>,
     extras: ExtrasSpecification,
     dev: bool,
     modifications: Modifications,
@@ -46,8 +48,17 @@ pub(crate) async fn sync(
         warn_user_once!("`uv sync` is experimental and may change without warning");
     }
 
-    // Identify the project
-    let project = VirtualProject::discover(&CWD, &DiscoveryOptions::default()).await?;
+    // Identify the project.
+    let project = if let Some(package) = package {
+        VirtualProject::Project(
+            Workspace::discover(&CWD, &DiscoveryOptions::default())
+                .await?
+                .with_current_project(package.clone())
+                .with_context(|| format!("Package `{package}` not found in workspace"))?,
+        )
+    } else {
+        VirtualProject::discover(&CWD, &DiscoveryOptions::default()).await?
+    };
 
     // Discover or create the virtual environment.
     let venv = project::get_or_init_environment(

crates/uv/src/lib.rs

@@ -979,6 +979,7 @@ async fn run_project(
             commands::sync(
                 args.locked,
                 args.frozen,
+                args.package,
                 args.extras,
                 args.dev,
                 args.modifications,

crates/uv/src/settings.rs

@@ -543,6 +543,7 @@ pub(crate) struct SyncSettings {
     pub(crate) extras: ExtrasSpecification,
     pub(crate) dev: bool,
     pub(crate) modifications: Modifications,
+    pub(crate) package: Option<PackageName>,
     pub(crate) python: Option<String>,
     pub(crate) refresh: Refresh,
     pub(crate) settings: ResolverInstallerSettings,
@@ -564,6 +565,7 @@ impl SyncSettings {
             installer,
             build,
             refresh,
+            package,
             python,
         } = args;
 
@@ -582,6 +584,7 @@ impl SyncSettings {
             ),
             dev: flag(dev, no_dev).unwrap_or(true),
             modifications,
+            package,
             python,
             refresh: Refresh::from(refresh),
             settings: ResolverInstallerSettings::combine(

crates/uv/tests/sync.rs

@@ -205,3 +205,69 @@ fn empty() -> Result<()> {
 
     Ok(())
 }
+
+/// Sync an individual package within a workspace.
+#[test]
+fn package() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "root"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["child", "anyio>3"]
+
+        [tool.uv.sources]
+        child = { workspace = true }
+
+        [tool.uv.workspace]
+        members = ["child"]
+        "#,
+    )?;
+
+    let src = context.temp_dir.child("src").child("albatross");
+    src.create_dir_all()?;
+
+    let init = src.child("__init__.py");
+    init.touch()?;
+
+    let child = context.temp_dir.child("child");
+    fs_err::create_dir_all(&child)?;
+
+    let pyproject_toml = child.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "child"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig>1"]
+        "#,
+    )?;
+
+    let src = child.child("src").child("albatross");
+    src.create_dir_all()?;
+
+    let init = src.child("__init__.py");
+    init.touch()?;
+
+    uv_snapshot!(context.filters(), context.sync().arg("--package").arg("child"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning
+    warning: `uv.sources` is experimental and may change without warning
+    Resolved 6 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + child==0.1.0 (from file://[TEMP_DIR]/child)
+     + iniconfig==2.0.0
+    "###);
+
+    Ok(())
+}