chore: set recursion call limit to sub_unify

crates/erg_compiler/context/unify.rs

@@ -2,6 +2,7 @@
 use std::iter::repeat;
 use std::mem;
 use std::option::Option;
+use std::sync::atomic::{AtomicUsize, Ordering};
 
 use erg_common::consts::DEBUG_MODE;
 use erg_common::fresh::FRESH_GEN;
@@ -33,6 +34,7 @@ pub struct Unifier<'c, 'l, 'u, L: Locational> {
     loc: &'l L,
     undoable: Option<&'u UndoableLinkedList>,
     change_generalized: bool,
+    recursion_limit: AtomicUsize,
     param_name: Option<Str>,
 }
 
@@ -49,6 +51,7 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
             loc,
             undoable,
             change_generalized,
+            recursion_limit: AtomicUsize::new(128),
             param_name,
         }
     }
@@ -945,6 +948,18 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
     /// ```
     fn sub_unify(&self, maybe_sub: &Type, maybe_sup: &Type) -> TyCheckResult<()> {
         log!(info "trying {}sub_unify:\nmaybe_sub: {maybe_sub}\nmaybe_sup: {maybe_sup}", self.undoable.map_or("", |_| "undoable_"));
+        self.recursion_limit.fetch_sub(1, Ordering::SeqCst);
+        if self.recursion_limit.load(Ordering::SeqCst) == 0 {
+            log!(err "recursion limit exceeded: {maybe_sub} / {maybe_sup}");
+            return Err(TyCheckError::recursion_limit(
+                self.ctx.cfg.input.clone(),
+                line!() as usize,
+                self.loc.loc(),
+                fn_name!(),
+                line!(),
+            )
+            .into());
+        }
         // In this case, there is no new information to be gained
         // この場合、特に新しく得られる情報はない
         if maybe_sub == &Type::Never || maybe_sup == &Type::Obj || maybe_sup.addr_eq(maybe_sub) {

crates/erg_compiler/error/tycheck.rs

@@ -53,6 +53,31 @@ impl TyCheckError {
         )
     }
 
+    pub fn recursion_limit(
+        input: Input,
+        errno: usize,
+        loc: Location,
+        fn_name: &str,
+        line: u32,
+    ) -> Self {
+        Self::new(
+            ErrorCore::new(
+                vec![SubMessage::only_loc(loc)],
+                switch_lang!(
+                    "japanese" => format!("コンパイラ内部の再帰呼び出し回数が上限に達しました。これはErg compilerのバグです、開発者に報告して下さい ({URL})\n\n{fn_name}:{line}より発生"),
+                    "simplified_chinese" => format!("编译器内部的递归调用次数已达到上限。这是Erg编译器的错误，请报告给{URL}\n\n原因来自: {fn_name}:{line}"),
+                    "traditional_chinese" => format!("編譯器內部的遞歸調用次數已達到上限。這是Erg編譯器的錯誤，請報告給{URL}\n\n原因來自: {fn_name}:{line}"),
+                    "english" => format!("the number of recursive calls in the compiler has reached the limit. This is a bug of the Erg compiler, please report it to {URL}\n\ncaused from: {fn_name}:{line}"),
+                ),
+                errno,
+                CompilerSystemError,
+                loc,
+            ),
+            input,
+            "".to_string(),
+        )
+    }
+
     pub fn no_type_spec_error(
         input: Input,
         errno: usize,