Replace common functionality with rust implementation

mgr/src/dirs.rs

@@ -0,0 +1,29 @@
+use std::path::PathBuf;
+
+use thiserror::Error;
+
+use super::env;
+
+const ENV_XDG_RUNTIME_DIR: &str = "XDG_RUNTIME_DIR";
+const ENV_XDG_CACHE_DIR: &str = "XDG_CACHE_HOME";
+
+#[derive(Debug, Error)]
+pub enum Error {
+    #[error(transparent)]
+    Env(#[from] env::Error),
+}
+
+pub(crate) fn xdg_runtime_dir() -> Result<Option<PathBuf>, Error> {
+    Ok(env::get(ENV_XDG_RUNTIME_DIR)?.map(PathBuf::from))
+}
+
+pub(crate) fn require_xdg_runtime_dir() -> Result<PathBuf, Error> {
+    Ok(PathBuf::from(env::require(ENV_XDG_RUNTIME_DIR)?))
+}
+
+pub(crate) fn xdg_cache_dir() -> Result<PathBuf, Error> {
+    Ok(match env::get(ENV_XDG_CACHE_DIR)? {
+        Some(value) => PathBuf::from(value),
+        None => PathBuf::from(env::require("HOME")?).join(".cache"),
+    })
+}