Make parsing of _VERSION global more robust

src/lune/globals/version.rs

@@ -1,24 +1,39 @@
 use mlua::prelude::*;
 
 pub fn create(lua: &Lua) -> LuaResult<impl IntoLua<'_>> {
+    let lune_version = format!("Lune {}", env!("CARGO_PKG_VERSION"));
+
     let luau_version_full = lua
         .globals()
         .get::<_, LuaString>("_VERSION")
         .expect("Missing _VERSION global");
+    let luau_version_str = luau_version_full
+        .to_str()
+        .context("Invalid utf8 found in _VERSION global")?;
 
-    let luau_version = luau_version_full
-        .to_str()?
-        .strip_prefix("Luau 0.")
-        .expect("_VERSION global is formatted incorrectly")
-        .trim();
-
-    if luau_version.is_empty() {
-        panic!("_VERSION global is missing version number")
+    // If this function runs more than once, we
+    // may get an already formatted lune version.
+    if luau_version_str.starts_with(&lune_version) {
+        return Ok(luau_version_full);
     }
 
-    lua.create_string(format!(
-        "Lune {lune}+{luau}",
-        lune = env!("CARGO_PKG_VERSION"),
-        luau = luau_version,
-    ))
+    // Luau version is expected to be in the format "Luau 0.x" and sometimes "Luau 0.x.y"
+    if !luau_version_str.starts_with("Luau 0.") {
+        panic!("_VERSION global is formatted incorrectly\nGot: '{luau_version_str}'")
+    }
+    let luau_version = luau_version_str.strip_prefix("Luau 0.").unwrap().trim();
+
+    // We make some guarantees about the format of the _VERSION global,
+    // so make sure that the luau version also follows those rules.
+    if luau_version.is_empty() {
+        panic!("_VERSION global is missing version number\nGot: '{luau_version_str}'")
+    } else if !luau_version.chars().all(is_valid_version_char) {
+        panic!("_VERSION global contains invalid characters\nGot: '{luau_version_str}'")
+    }
+
+    lua.create_string(format!("{lune_version}+{luau_version}"))
+}
+
+fn is_valid_version_char(c: char) -> bool {
+    matches!(c, '0'..='9' | '.')
 }