feat(layout): Support environment variables in cwd (zellij-org#2288)

* add `shellexpand` as dependency
* expand environment variable in kdl parser's `parse_cwd()`

zellij-utils/Cargo.toml

@@ -38,6 +38,7 @@ miette = { version = "3.3.0", features = ["fancy"] }
 regex = "1.5.5"
 tempfile = "3.2.0"
 kdl = { version = "4.5.0", features = ["span"] }
+shellexpand = "3.0.0"
 
 #[cfg(not(target_family = "wasm"))]
 [target.'cfg(not(target_family = "wasm"))'.dependencies]

zellij-utils/src/input/unit/layout_test.rs

@@ -2031,3 +2031,35 @@ fn run_plugin_location_parsing() {
     };
     assert_eq!(layout, expected_layout);
 }
+
+fn get_cwd(layout: &Layout) -> Option<&PathBuf> {
+    match layout.template.as_ref()?.0.children.get(0)?.run.as_ref()? {
+        Run::Cwd(cwd) => Some(cwd),
+        _ => None,
+    }
+}
+
+#[test]
+fn pane_cwd_valid_env_var() {
+    let kdl_layout = r#"
+        layout {
+            pane cwd="$ZELLIJ_FOO/foo"
+        }
+    "#;
+    std::env::set_var("ZELLIJ_FOO", "/test_cwd");
+    let layout = Layout::from_kdl(kdl_layout, "layout_file_name".into(), None, None).unwrap();
+    let cwd = get_cwd(&layout).unwrap();
+    assert_eq!(cwd.to_string_lossy(), "/test_cwd/foo");
+}
+
+#[test]
+fn pane_cwd_invalid_env_var() {
+    let kdl_layout = r#"
+        layout {
+            pane cwd="$ZELLIJ_BAR/foo"
+        }
+    "#;
+    std::env::remove_var("ZELLIJ_BAR");
+    let layout = Layout::from_kdl(kdl_layout, "layout_file_name".into(), None, None).unwrap();
+    assert_eq!(get_cwd(&layout), None);
+}

zellij-utils/src/kdl/kdl_layout_parser.rs

@@ -334,6 +334,13 @@ impl<'a> KdlLayoutParser<'a> {
     fn parse_cwd(&self, kdl_node: &KdlNode) -> Result<Option<PathBuf>, ConfigError> {
         Ok(
             kdl_get_string_property_or_child_value_with_error!(kdl_node, "cwd")
+                .and_then(|cwd| match shellexpand::env(cwd) {
+                    Ok(cwd) => Some(cwd.to_string()),
+                    Err(e) => {
+                        log::error!("when parsing `cwd`: {}", e);
+                        None
+                    },
+                })
                 .map(|cwd| PathBuf::from(cwd)),
         )
     }