Improve `uv init` error for invalid directory names (#16554)

Resolves https://github.com/astral-sh/uv/issues/16433

When `uv init` infers a project name from the working directory,
directories with characters outside the PEP 503 rules produced the
generic “Not a valid package or extra name” message that didn’t explain
the source of the problem. This change intercepts that failure, reports
whether the current or explicit target directory caused it, and tells
the user to supply an explicit `--name`.

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

@@ -116,15 +116,27 @@ pub(crate) async fn init(
             let name = match name {
                 Some(name) => name,
                 None => {
-                    let name = path
+                    let directory_name = path
                         .file_name()
                         .and_then(|path| path.to_str())
                         .context("Missing directory name")?;
 
                     // Pre-normalize the package name by removing any leading or trailing
                     // whitespace, and replacing any internal whitespace with hyphens.
-                    let name = name.trim().replace(' ', "-");
-                    PackageName::from_owned(name)?
+                    let candidate = directory_name.trim().replace(' ', "-");
+                    match PackageName::from_owned(candidate) {
+                        Ok(name) => name,
+                        Err(_) => {
+                            let directory_description = if explicit_path.is_some() {
+                                "target directory"
+                            } else {
+                                "current directory"
+                            };
+                            anyhow::bail!(
+                                "The {directory_description} (`{directory_name}`) is not a valid package name. Please provide a package name with `--name`."
+                            );
+                        }
+                    }
                 }
             };
 

crates/uv/tests/it/init.rs

@@ -2659,10 +2659,32 @@ fn init_hidden() {
     ----- stdout -----
 
     ----- stderr -----
-    error: Not a valid package or extra name: ".foo". Names must start and end with a letter or digit and may only contain -, _, ., and alphanumeric characters.
+    error: The target directory (`.foo`) is not a valid package name. Please provide a package name with `--name`.
     "###);
 }
 
+#[test]
+fn init_non_ascii_directory() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let directory = context.temp_dir.child("püthon");
+    directory.create_dir_all()?;
+
+    let mut command = context.init();
+    command.current_dir(directory.path());
+
+    uv_snapshot!(context.filters(), command, @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: The current directory (`püthon`) is not a valid package name. Please provide a package name with `--name`.
+    "###);
+
+    Ok(())
+}
+
 /// Run `uv init` with an invalid `pyproject.toml` in a parent directory.
 #[test]
 fn init_failure() -> Result<()> {