Add __tostring to error object

src/error.rs

@@ -1,6 +1,11 @@
+use anyhow::Result;
 use gmod::*;
 use sqlx::mysql::MySqlDatabaseError;
 
+use crate::cstr_from_args;
+
+const META_NAME: LuaCStr = cstr_from_args!(crate::GLOBAL_TABLE_NAME, "_error");
+
 // call this function after creating a table
 fn handle_database_error(l: lua::State, db_e: &MySqlDatabaseError) -> String {
     if let Some(sqlstate) = db_e.code() {
@@ -32,6 +37,8 @@ fn handle_sqlx_error_internal(l: lua::State, e: &sqlx::Error) -> String {
 
 pub fn handle_error(l: lua::State, e: anyhow::Error) -> String {
     l.create_table(0, 3);
+    l.get_metatable_name(META_NAME);
+    unsafe { l.set_metatable(-2) };
 
     let msg = match e.downcast_ref::<sqlx::Error>() {
         Some(sqlx_e) => handle_sqlx_error_internal(l, sqlx_e),
@@ -46,6 +53,37 @@ pub fn handle_error(l: lua::State, e: anyhow::Error) -> String {
 
 pub fn handle_sqlx_error(l: lua::State, e: sqlx::Error) -> String {
     l.create_table(0, 3);
+    l.get_metatable_name(META_NAME);
+    unsafe { l.set_metatable(-2) };
 
     handle_sqlx_error_internal(l, &e)
 }
+
+#[lua_function]
+fn __tostring(l: lua::State) -> Result<i32> {
+    // retrieve the code field and the message field
+    l.get_field(-1, c"code");
+    let code = l.check_number(-1);
+    l.pop();
+
+    l.get_field(-1, c"message");
+    let message = l.check_string(-1); // copy the string
+
+    let message = message.or_else(|_| anyhow::Ok("unknown error".into()))?;
+    if let Ok(code) = code {
+        l.push_string(&format!("({}) {}", code, message));
+    } else {
+        l.push_string(&message);
+    }
+
+    Ok(1)
+}
+
+pub fn init(l: lua::State) {
+    l.new_metatable(META_NAME);
+    {
+        l.push_function(__tostring);
+        l.set_field(-2, c"__tostring");
+    }
+    l.pop();
+}

src/lib.rs

@@ -37,6 +37,7 @@ fn gmod13_open(l: lua::State) -> i32 {
     runtime::load(get_max_worker_threads(l));
 
     conn::on_gmod_open::init(l);
+    error::init(l);
 
     0
 }