use std::{ffi::OsString, path::PathBuf}; use crate::Source; impl Source {    /// Produce a storage location for the this source while potentially querying environment variables using `env_var(<name>)`,    /// or `None` if the storage location could not be obtained.    ///    /// Note that local sources are returned as relative paths to be joined with the base in a separate step.    pub fn storage_location(self, env_var: &mut dyn FnMut(&str) -> Option<OsString>) -> Option<PathBuf> {        use Source::*;        Some(match self {            GitInstallation => gix_path::env::installation_config_prefix()?.join("gitattributes"),            System => {                if env_var("GIT_ATTR_NOSYSTEM").is_some() {                    return None;                } else {                    gix_path::env::system_prefix()?.join("etc/gitattributes")                }            }            Git => return gix_path::env::xdg_config("attributes", env_var),            Local => PathBuf::from("info/attributes"),        })    }}