Expanding envs in language config

helix-loader/Cargo.toml

@@ -31,6 +31,7 @@ log = "0.4"
 cc = { version = "1" }
 threadpool = { version = "1.0" }
 tempfile.workspace = true
+regex = "1.11.1"
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 libloading = "0.8"

helix-loader/src/config.rs

@@ -1,4 +1,5 @@
 use std::str::from_utf8;
+use crate::env_expander::get_env_expanded_toml;
 
 /// Default built-in languages.toml.
 pub fn default_lang_config() -> toml::Value {
@@ -17,7 +18,7 @@ pub fn user_lang_config() -> Result<toml::Value, toml::de::Error> {
     .map(|path| path.join("languages.toml"))
     .filter_map(|file| {
         std::fs::read_to_string(file)
-            .map(|config| toml::from_str(&config))
+            .map(|config| get_env_expanded_toml(&config))
             .ok()
     })
     .collect::<Result<Vec<_>, _>>()?

helix-loader/src/env_expander.rs

@@ -0,0 +1,91 @@
+use regex::Regex;
+use std::env;
+use std::str::FromStr;
+
+#[derive(Debug)]
+enum AllowedEnv {
+    Home,
+    User,
+    ConfigDir,
+}
+
+impl FromStr for AllowedEnv {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "HOME" => Ok(AllowedEnv::Home),
+            "USER" => Ok(AllowedEnv::User),
+            "CONFIG_DIR" => Ok(AllowedEnv::ConfigDir),
+            _ => Err(()),
+        }
+    }
+}
+
+/// Expands AllowedEnv variables in the input string.
+/// Allowed patterns are in the format `${VAR_NAME}`.
+pub fn expand_env_vars(input: &str) -> String {
+    let re = Regex::new(r"\$\{(\w+)\}").expect("Invalid regex");
+
+    re.replace_all(input, |caps: &regex::Captures| {
+        let var_name = &caps[1];
+        if let Ok(_allowed) = var_name.parse::<AllowedEnv>() {
+            env::var(var_name).unwrap_or_else(|_| "".to_string())
+        } else {
+            caps.get(0)
+                .map_or("".to_string(), |m| m.as_str().to_string())
+        }
+    })
+    .into_owned()
+}
+
+pub fn get_env_expanded_toml<T>(toml_str: &str) -> Result<T, toml::de::Error>
+where
+    T: serde::de::DeserializeOwned
+{
+    match std::env::consts::OS {
+        "linux" => toml::from_str(&expand_env_vars(toml_str)),
+        _ => toml::from_str(toml_str),
+    }
+
+}
+
+#[cfg(test)]
+mod env_expander_tests {
+    use toml::Value;
+    use std::env;
+    use super::get_env_expanded_toml;
+
+    #[test]
+    fn expand_envs_and_parse_toml() {
+        let toml_text = r#"
+            title = "My App"
+            dir = "${HOME}/project/source"
+            user = "${USER}"
+            config = "${CONFIG_DIR}"
+            unknown = "${NOT_ALLOWED}"
+        "#;
+
+        env::set_var("HOME", "/home/example");
+        env::set_var("USER", "example_user");
+        env::set_var("CONFIG_DIR", "/etc/myapp");
+
+        let parsed: Value = get_env_expanded_toml(toml_text).unwrap();
+        assert_eq!(
+            parsed["dir"],
+            "/home/example/project/source".into()
+        );
+        assert_eq!(
+            parsed["user"],
+            "example_user".into()
+        );
+        assert_eq!(
+            parsed["config"],
+            "/etc/myapp".into()
+        );
+        assert_eq!(
+            parsed["unknown"],
+            "${NOT_ALLOWED}".into()
+        );
+    }
+}
+

helix-loader/src/lib.rs

@@ -1,5 +1,6 @@
 pub mod config;
 pub mod grammar;
+pub mod env_expander;
 
 use helix_stdx::{env::current_working_dir, path};