fix: infinite recursion bug

crates/erg_common/shared.rs

@@ -1,5 +1,6 @@
 use std::fmt;
 use std::hash::{Hash, Hasher};
+use std::sync::atomic::{AtomicU32, Ordering};
 use std::thread::ThreadId;
 // use std::rc::Rc;
 pub use parking_lot::{
@@ -292,6 +293,7 @@ pub struct Forkable<T: Send + Clone> {
     last_borrowed_at: Arc<ThreadLocal<RefCell<BorrowInfo>>>,
     #[cfg(any(feature = "backtrace", feature = "debug"))]
     last_mut_borrowed_at: Arc<ThreadLocal<RefCell<BorrowInfo>>>,
+    recursion_counter: Arc<AtomicU32>,
 }
 
 impl<T: fmt::Debug + Send + Clone> fmt::Debug for Forkable<T> {
@@ -326,9 +328,18 @@ impl<T: Send + Clone> Forkable<T> {
             last_borrowed_at: Arc::new(ThreadLocal::new()),
             #[cfg(any(feature = "backtrace", feature = "debug"))]
             last_mut_borrowed_at: Arc::new(ThreadLocal::new()),
+            recursion_counter: Arc::new(AtomicU32::new(0)),
         }
     }
 
+    /// return 1 if the recursion limit is reached.
+    pub fn dec_recursion_counter(&self) -> u32 {
+        if self.recursion_counter.load(Ordering::SeqCst) == 0 {
+            self.recursion_counter.store(256, Ordering::SeqCst);
+        }
+        self.recursion_counter.fetch_sub(1, Ordering::SeqCst)
+    }
+
     pub fn update_init(&mut self) {
         let clone = self.clone_inner();
         // NG: self.init = Arc::new(clone);

crates/erg_compiler/ty/free.rs

@@ -551,6 +551,9 @@ pub struct Free<T: Send + Clone>(Forkable<FreeKind<T>>);
 
 impl Hash for Free<Type> {
     fn hash<H: Hasher>(&self, state: &mut H) {
+        if self.0.dec_recursion_counter() == 1 {
+            return;
+        }
         if let Some(name) = self.unbound_name() {
             name.hash(state);
         }