Add --config-file support (#3047)

## Summary

Users can now pass a config file on the command line, e.g., with
`--config-file /path/to/file.py`.

crates/uv-workspace/src/workspace.rs

@@ -21,7 +21,7 @@ impl Workspace {
     /// found.
     pub fn find(path: impl AsRef<Path>) -> Result<Option<Self>, WorkspaceError> {
         for ancestor in path.as_ref().ancestors() {
-            match read_options(ancestor) {
+            match find_in_directory(ancestor) {
                 Ok(Some(options)) => {
                     return Ok(Some(Self {
                         options,
@@ -43,10 +43,18 @@ impl Workspace {
         }
         Ok(None)
     }
+
+    /// Load a [`Workspace`] from a `pyproject.toml` or `uv.toml` file.
+    pub fn from_file(path: impl AsRef<Path>) -> Result<Self, WorkspaceError> {
+        Ok(Self {
+            options: read_file(path.as_ref())?,
+            root: path.as_ref().parent().unwrap().to_path_buf(),
+        })
+    }
 }
 
 /// Read a `uv.toml` or `pyproject.toml` file in the given directory.
-fn read_options(dir: &Path) -> Result<Option<Options>, WorkspaceError> {
+fn find_in_directory(dir: &Path) -> Result<Option<Options>, WorkspaceError> {
     // Read a `uv.toml` file in the current directory.
     let path = dir.join("uv.toml");
     match fs_err::read_to_string(&path) {
@@ -94,6 +102,20 @@ fn read_options(dir: &Path) -> Result<Option<Options>, WorkspaceError> {
     Ok(None)
 }
 
+/// Load [`Options`] from a `pyproject.toml` or `ruff.toml` file.
+fn read_file(path: &Path) -> Result<Options, WorkspaceError> {
+    let content = fs_err::read_to_string(path)?;
+    if path.ends_with("pyproject.toml") {
+        let pyproject: PyProjectToml = toml::from_str(&content)
+            .map_err(|err| WorkspaceError::PyprojectToml(path.user_display().to_string(), err))?;
+        Ok(pyproject.tool.and_then(|tool| tool.uv).unwrap_or_default())
+    } else {
+        let options: Options = toml::from_str(&content)
+            .map_err(|err| WorkspaceError::UvToml(path.user_display().to_string(), err))?;
+        Ok(options)
+    }
+}
+
 #[derive(thiserror::Error, Debug)]
 pub enum WorkspaceError {
     #[error(transparent)]

crates/uv/src/cli.rs

@@ -30,6 +30,10 @@ pub(crate) struct Cli {
 
     #[command(flatten)]
     pub(crate) cache_args: CacheArgs,
+
+    /// The path to a `pyproject.toml` or `uv.toml` file to use for configuration.
+    #[arg(long, short, env = "UV_CONFIG_FILE", hide = true)]
+    pub(crate) config_file: Option<PathBuf>,
 }
 
 #[derive(Parser, Debug, Clone)]

crates/uv/src/main.rs

@@ -110,7 +110,11 @@ async fn run() -> Result<ExitStatus> {
     };
 
     // Load the workspace settings.
-    let workspace = uv_workspace::Workspace::find(env::current_dir()?)?;
+    let workspace = if let Some(config_file) = cli.config_file.as_ref() {
+        Some(uv_workspace::Workspace::from_file(config_file)?)
+    } else {
+        uv_workspace::Workspace::find(env::current_dir()?)?
+    };
 
     // Resolve the global settings.
     let globals = GlobalSettings::resolve(cli.global_args, workspace.as_ref());