support `--no-project` in `uv format` (#15572)

When a user passes `--no-project` argument to `uv format` command,
instead of running the formatter in the context of the current project,
run it in the context of the current directory. This is useful when the
current directory is not a project.

Closes https://github.com/astral-sh/uv/issues/15462

crates/uv-cli/src/lib.rs

@@ -4461,6 +4461,14 @@ pub struct FormatArgs {
     /// `uv format -- src/module/foo.py` to format a specific file.
     #[arg(last = true)]
     pub extra_args: Vec<String>,
+
+    /// Avoid discovering a project or workspace.
+    ///
+    /// Instead of running the formatter in the context of the current project, run it in the
+    /// context of the current directory. This is useful when the current directory is not a
+    /// project.
+    #[arg(long)]
+    pub no_project: bool,
 }
 
 #[derive(Args)]

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

@@ -29,6 +29,7 @@ pub(crate) async fn format(
     cache: Cache,
     printer: Printer,
     preview: Preview,
+    no_project: bool,
 ) -> Result<ExitStatus> {
     // Check if the format feature is in preview
     if !preview.is_enabled(PreviewFeatures::FORMAT) {
@@ -39,7 +40,11 @@ pub(crate) async fn format(
     }
 
     let workspace_cache = WorkspaceCache::default();
-    let target_dir =
+    // If `no_project` is provided, we use the provided directory
+    // Otherwise, we discover the project and use the project root.
+    let target_dir = if no_project {
+        project_dir.to_owned()
+    } else {
         match VirtualProject::discover(project_dir, &DiscoveryOptions::default(), &workspace_cache)
             .await
         {
@@ -53,7 +58,8 @@ pub(crate) async fn format(
                 | WorkspaceError::NonWorkspace(_),
             ) => project_dir.to_owned(),
             Err(err) => return Err(err.into()),
-        };
+        }
+    };
 
     // Parse version if provided
     let version = version.as_deref().map(Version::from_str).transpose()?;

crates/uv/src/lib.rs

@@ -2283,6 +2283,7 @@ async fn run_project(
                 cache,
                 printer,
                 globals.preview,
+                args.no_project,
             ))
             .await
         }

crates/uv/src/settings.rs

@@ -1911,6 +1911,7 @@ pub(crate) struct FormatSettings {
     pub(crate) diff: bool,
     pub(crate) extra_args: Vec<String>,
     pub(crate) version: Option<String>,
+    pub(crate) no_project: bool,
 }
 
 impl FormatSettings {
@@ -1921,6 +1922,7 @@ impl FormatSettings {
             diff,
             extra_args,
             version,
+            no_project,
         } = args;
 
         Self {
@@ -1928,6 +1930,7 @@ impl FormatSettings {
             diff,
             extra_args,
             version,
+            no_project,
         }
     }
 }

crates/uv/tests/it/format.rs

@@ -187,6 +187,34 @@ fn format_from_project_root() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn format_no_project() -> Result<()> {
+    let context = TestContext::new_with_versions(&[]);
+
+    let main_py = context.temp_dir.child("main.py");
+    main_py.write_str(indoc! {r"
+        x    = 1
+    "})?;
+
+    uv_snapshot!(context.filters(), context.format().arg("--no-project"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    1 file reformatted
+
+    ----- stderr -----
+    warning: `uv format` is experimental and may change without warning. Pass `--preview-features format` to disable this warning.
+    ");
+
+    // Check that the file was formatted
+    let formatted_content = fs_err::read_to_string(&main_py)?;
+    assert_snapshot!(formatted_content, @r"
+        x = 1
+    ");
+
+    Ok(())
+}
+
 #[test]
 fn format_relative_project() -> Result<()> {
     let context = TestContext::new_with_versions(&[]);

docs/reference/cli.md

@@ -2279,7 +2279,9 @@ uv format [OPTIONS] [-- <EXTRA_ARGS>...]
 <p>Instead, uv will search for a suitable Python version on the system.</p>
 <p>May also be set with the <code>UV_NO_MANAGED_PYTHON</code> environment variable.</p></dd><dt id="uv-format--no-progress"><a href="#uv-format--no-progress"><code>--no-progress</code></a></dt><dd><p>Hide all progress outputs.</p>
 <p>For example, spinners or progress bars.</p>
-<p>May also be set with the <code>UV_NO_PROGRESS</code> environment variable.</p></dd><dt id="uv-format--no-python-downloads"><a href="#uv-format--no-python-downloads"><code>--no-python-downloads</code></a></dt><dd><p>Disable automatic downloads of Python.</p>
+<p>May also be set with the <code>UV_NO_PROGRESS</code> environment variable.</p></dd><dt id="uv-format--no-project"><a href="#uv-format--no-project"><code>--no-project</code></a></dt><dd><p>Avoid discovering a project or workspace.</p>
+<p>Instead of running the formatter in the context of the current project, run it in the context of the current directory. This is useful when the current directory is not a project.</p>
+</dd><dt id="uv-format--no-python-downloads"><a href="#uv-format--no-python-downloads"><code>--no-python-downloads</code></a></dt><dd><p>Disable automatic downloads of Python.</p>
 </dd><dt id="uv-format--offline"><a href="#uv-format--offline"><code>--offline</code></a></dt><dd><p>Disable network access.</p>
 <p>When disabled, uv will only use locally cached data and locally available files.</p>
 <p>May also be set with the <code>UV_OFFLINE</code> environment variable.</p></dd><dt id="uv-format--project"><a href="#uv-format--project"><code>--project</code></a> <i>project</i></dt><dd><p>Run the command within the given project directory.</p>