uv init ignores workspace when --isolated flag is used (#5290)

## Summary

Per #5250 (comment)

> It would also be great to have an argument (perhaps leveraging the
global isolated option) that allows us to disable workspace discovery
when we don't want to add a project as a member.


## Test Plan

```sh

$cargo run -- init work
$ cargo run -- init work/pkg-a --isolated
warning: `uv init` is experimental and may change without warning
Initialized project sub-c in /tmp/work
```

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

@@ -19,18 +19,17 @@ pub(crate) async fn init(
     explicit_path: Option<String>,
     name: Option<PackageName>,
     no_readme: bool,
+    isolated: bool,
     preview: PreviewMode,
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
         warn_user_once!("`uv init` is experimental and may change without warning");
     }
 
-    let current_dir = std::env::current_dir()?.canonicalize()?;
-
     // Default to the current directory if a path was not provided.
     let path = match explicit_path {
-        None => current_dir.clone(),
+        None => std::env::current_dir()?.canonicalize()?,
         Some(ref path) => PathBuf::from(path),
     };
 
@@ -67,10 +66,14 @@ pub(crate) async fn init(
     let path = path.canonicalize()?;
 
     // Discover the current workspace, if it exists.
-    let workspace = match ProjectWorkspace::discover(&path, None).await {
-        Ok(project) => Some(project),
-        Err(WorkspaceError::MissingPyprojectToml) => None,
-        Err(err) => return Err(err.into()),
+    let workspace = if isolated {
+        None
+    } else {
+        match ProjectWorkspace::discover(&path, None).await {
+            Ok(project) => Some(project),
+            Err(WorkspaceError::MissingPyprojectToml) => None,
+            Err(err) => return Err(err.into()),
+        }
     };
 
     // Create the `pyproject.toml`.

crates/uv/src/lib.rs

@@ -834,6 +834,7 @@ async fn run_project(
                 args.path,
                 args.name,
                 args.no_readme,
+                globals.isolated,
                 globals.preview,
                 printer,
             )

crates/uv/tests/init.rs

@@ -511,3 +511,48 @@ fn init_invalid_names() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn init_workspace_isolated() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        "#,
+    })?;
+
+    let child = context.temp_dir.join("foo");
+    fs_err::create_dir(&child)?;
+
+    uv_snapshot!(context.filters(), context.init().current_dir(&child).arg("--isolated"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv init` is experimental and may change without warning
+    Initialized project foo
+    "###);
+
+    let workspace = fs_err::read_to_string(context.temp_dir.join("pyproject.toml"))?;
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            workspace, @r###"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        "###
+        );
+    });
+
+    Ok(())
+}