Add uv run --no-sync (#7192)

## Summary

When `--no-sync` is provided, we won't lock or sync, but we will run the
command in the project environment.

Closes https://github.com/astral-sh/uv/issues/7165.

crates/uv-cli/src/lib.rs

@@ -2434,6 +2434,13 @@ pub struct RunArgs {
     #[arg(long)]
     pub isolated: bool,
 
+    /// Avoid syncing the virtual environment.
+    ///
+    /// Implies `--frozen`, as the project dependencies will be ignored (i.e., the lockfile will not
+    /// be updated, since the environment will not be synced regardless).
+    #[arg(long, conflicts_with = "frozen")]
+    pub no_sync: bool,
+
     /// Assert that the `uv.lock` will remain unchanged.
     ///
     /// Requires that the lockfile is up-to-date. If the lockfile is missing or
@@ -2735,7 +2742,7 @@ pub struct AddArgs {
     #[arg(long)]
     pub extra: Option<Vec<ExtraName>>,
 
-    /// Avoid syncing the virtual environment after re-locking the project.
+    /// Avoid syncing the virtual environment.
     #[arg(long, conflicts_with = "frozen")]
     pub no_sync: bool,
 

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

@@ -49,6 +49,7 @@ pub(crate) async fn run(
     show_resolution: bool,
     locked: bool,
     frozen: bool,
+    no_sync: bool,
     isolated: bool,
     package: Option<PackageName>,
     no_project: bool,
@@ -258,6 +259,11 @@ pub(crate) async fn run(
                 "`--frozen` is a no-op for Python scripts with inline metadata, which always run in isolation"
             );
         }
+        if no_sync {
+            warn_user!(
+                "`--no-sync` is a no-op for Python scripts with inline metadata, which always run in isolation"
+            );
+        }
         if isolated {
             warn_user!(
                 "`--isolated` is a no-op for Python scripts with inline metadata, which always run in isolation"
@@ -318,6 +324,9 @@ pub(crate) async fn run(
             if frozen {
                 warn_user!("`--frozen` has no effect when used alongside `--no-project`");
             }
+            if no_sync {
+                warn_user!("`--no-sync` has no effect when used alongside `--no-project`");
+            }
         } else if project.is_none() {
             // If we can't find a project and the user provided a project-only setting, warn.
             if !extras.is_empty() {
@@ -329,8 +338,8 @@ pub(crate) async fn run(
             if locked {
                 warn_user!("`--locked` has no effect when used outside of a project");
             }
-            if frozen {
-                warn_user!("`--frozen` has no effect when used outside of a project");
+            if no_sync {
+                warn_user!("`--no-sync` has no effect when used outside of a project");
             }
         }
 
@@ -414,6 +423,9 @@ pub(crate) async fn run(
                 .await?
             };
 
+            if no_sync {
+                debug!("Skipping environment synchronization due to `--no-sync`");
+            } else {
                 let result = match project::lock::do_safe_lock(
                     locked,
                     frozen,
@@ -468,6 +480,7 @@ pub(crate) async fn run(
                     printer,
                 )
                 .await?;
+            }
 
             venv.into_interpreter()
         } else {

crates/uv/src/lib.rs

@@ -1123,6 +1123,7 @@ async fn run_project(
                 args.show_resolution || globals.verbose > 0,
                 args.locked,
                 args.frozen,
+                args.no_sync,
                 args.isolated,
                 args.package,
                 args.no_project,

crates/uv/src/settings.rs

@@ -217,6 +217,7 @@ pub(crate) struct RunSettings {
     pub(crate) show_resolution: bool,
     pub(crate) package: Option<PackageName>,
     pub(crate) no_project: bool,
+    pub(crate) no_sync: bool,
     pub(crate) python: Option<String>,
     pub(crate) refresh: Refresh,
     pub(crate) settings: ResolverInstallerSettings,
@@ -237,6 +238,7 @@ impl RunSettings {
             with_editable,
             with_requirements,
             isolated,
+            no_sync,
             locked,
             frozen,
             installer,
@@ -266,6 +268,7 @@ impl RunSettings {
             show_resolution,
             package,
             no_project,
+            no_sync,
             python,
             refresh: Refresh::from(refresh),
             settings: ResolverInstallerSettings::combine(

crates/uv/tests/run.rs

@@ -976,6 +976,62 @@ fn run_frozen() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn run_no_sync() -> 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 = ["anyio==3.7.0"]
+
+        [build-system]
+        requires = ["setuptools>=42"]
+        build-backend = "setuptools.build_meta"
+        "#,
+    )?;
+
+    // Running with `--no-sync` should succeed error, even if the lockfile isn't present.
+    uv_snapshot!(context.filters(), context.run().arg("--no-sync").arg("--").arg("python").arg("--version"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Python 3.12.[X]
+
+    ----- stderr -----
+    "###);
+
+    context.lock().assert().success();
+
+    // Running with `--no-sync` should not install any requirements.
+    uv_snapshot!(context.filters(), context.run().arg("--no-sync").arg("--").arg("python").arg("--version"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Python 3.12.[X]
+
+    ----- stderr -----
+    "###);
+
+    context.sync().assert().success();
+
+    // But it should have access to the installed packages.
+    uv_snapshot!(context.filters(), context.run().arg("--no-sync").arg("--").arg("python").arg("-c").arg("import anyio; print(anyio.__name__)"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    anyio
+
+    ----- stderr -----
+    "###);
+
+    Ok(())
+}
+
 #[test]
 fn run_empty_requirements_txt() -> Result<()> {
     let context = TestContext::new("3.12");

docs/concepts/projects.md

@@ -358,6 +358,8 @@ and not usable by other tools.
 
 To avoid updating the lockfile during `uv sync` and `uv run` invocations, use the `--frozen` flag.
 
+To avoid updating the environment during `uv run` invocations, use the `--no-sync` flag.
+
 To assert the lockfile matches the project metadata, use the `--locked` flag. If the lockfile is not
 up-to-date, an error will be raised instead of updating the lockfile.
 

docs/reference/cli.md

@@ -265,6 +265,10 @@ uv run [OPTIONS] <COMMAND>
 
 </dd><dt><code>--no-sources</code></dt><dd><p>Ignore the <code>tool.uv.sources</code> table when resolving dependencies. Used to lock against the standards-compliant, publishable package metadata, as opposed to using any local or Git sources</p>
 
+</dd><dt><code>--no-sync</code></dt><dd><p>Avoid syncing the virtual environment.</p>
+
+<p>Implies <code>--frozen</code>, as the project dependencies will be ignored (i.e., the lockfile will not be updated, since the environment will not be synced regardless).</p>
+
 </dd><dt><code>--offline</code></dt><dd><p>Disable network access.</p>
 
 <p>When disabled, uv will only use locally cached data and locally available files.</p>
@@ -721,7 +725,7 @@ uv add [OPTIONS] <PACKAGES|--requirements <REQUIREMENTS>>
 
 </dd><dt><code>--no-sources</code></dt><dd><p>Ignore the <code>tool.uv.sources</code> table when resolving dependencies. Used to lock against the standards-compliant, publishable package metadata, as opposed to using any local or Git sources</p>
 
-</dd><dt><code>--no-sync</code></dt><dd><p>Avoid syncing the virtual environment after re-locking the project</p>
+</dd><dt><code>--no-sync</code></dt><dd><p>Avoid syncing the virtual environment</p>
 
 </dd><dt><code>--offline</code></dt><dd><p>Disable network access.</p>