fix: avoid infinite recursion

crates/erg_compiler/context/compare.rs

@@ -7,7 +7,7 @@ use erg_common::dict::Dict;
 use erg_common::set::Set;
 use erg_common::style::colors::DEBUG_ERROR;
 use erg_common::traits::StructuralEq;
-use erg_common::{assume_unreachable, fmt_vec, log, set, set_recursion_limit};
+use erg_common::{assume_unreachable, fmt_vec, log, set};
 use erg_common::{Str, Triple};
 
 use crate::context::eval::UndoableLinkedList;
@@ -359,7 +359,6 @@ impl Context {
     /// 単一化、評価等はここでは行わない、スーパータイプになる **可能性があるか** だけ判定する
     /// ので、lhsが(未連携)型変数の場合は単一化せずにtrueを返す
     pub(crate) fn structural_supertype_of(&self, lhs: &Type, rhs: &Type) -> bool {
-        set_recursion_limit!(false, 128);
         match (lhs, rhs) {
             // Proc :> Func if params are compatible
             // * default params can be omitted (e.g. (Int, x := Int) -> Int <: (Int) -> Int)
@@ -937,6 +936,11 @@ impl Context {
         }
     }
 
+    /// ```erg
+    /// Int.fields() == { imag: Int, real: Int, abs: (self: Int) -> Nat, ... }
+    /// ?T(<: Int).fields() == Int.fields()
+    /// Structural({ .x = Int }).fields() == { x: Int }
+    /// ```
     pub fn fields(&self, t: &Type) -> Dict<Field, Type> {
         match t {
             Type::FreeVar(fv) if fv.is_linked() => self.fields(&fv.unwrap_linked()),

crates/erg_compiler/context/unify.rs

@@ -2,14 +2,13 @@
 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;
 use erg_common::traits::Locational;
-use erg_common::Str;
 #[allow(unused_imports)]
 use erg_common::{dict, fmt_vec, fn_name, log};
+use erg_common::{get_hash, set_recursion_limit, Str};
 
 use crate::context::eval::Substituter;
 use crate::context::instantiate::TyVarCache;
@@ -35,7 +34,6 @@ 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>,
 }
 
@@ -52,7 +50,6 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
             loc,
             undoable,
             change_generalized,
-            recursion_limit: AtomicUsize::new(128),
             param_name,
         }
     }
@@ -1037,21 +1034,18 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
     /// ```
     fn sub_unify(&self, maybe_sub: &Type, maybe_super: &Type) -> TyCheckResult<()> {
         log!(info "trying {}sub_unify:\nmaybe_sub: {maybe_sub}\nmaybe_super: {maybe_super}", self.undoable.map_or("", |_| "undoable_"));
-        if self.recursion_limit.fetch_sub(1, Ordering::SeqCst) == 0 {
+        set_recursion_limit!(
-            self.recursion_limit.store(128, Ordering::SeqCst);
+            panic,
-            log!(err "recursion limit exceeded: {maybe_sub} / {maybe_super}");
+            "recursion limit exceed: sub_unify({maybe_sub}, {maybe_super})",
-            return Err(TyCheckError::recursion_limit(
+            128
-                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
-        if maybe_sub == &Type::Never || maybe_super == &Type::Obj || maybe_super.addr_eq(maybe_sub)
+            || maybe_super == &Type::Obj
+            || maybe_super.addr_eq(maybe_sub)
+            || (maybe_sub.has_no_unbound_var()
+                && maybe_super.has_no_unbound_var()
+                && maybe_sub == maybe_super)
         {
             log!(info "no-op:\nmaybe_sub: {maybe_sub}\nmaybe_super: {maybe_super}");
             return Ok(());
@@ -1481,8 +1475,11 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
                             .inspect_err(|_e| sub_fv.undo())?;
                     } else if !self.ctx.subtype_of(&sub, &Never) {
                         sub_fv.undo();
+                        let sub_hash = get_hash(maybe_sub);
                         maybe_sub.coerce(self.undoable);
-                        return self.sub_unify(maybe_sub, maybe_super);
+                        if get_hash(maybe_sub) != sub_hash {
+                            return self.sub_unify(maybe_sub, maybe_super);
+                        }
                     } else {
                         // e.g. ?T / Structural({ .method = (self: ?T) -> Int })
                         let constr = Constraint::new_sandwiched(
@@ -1518,23 +1515,27 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
                     }
                     let sub = mem::take(&mut sub);
                     // min(L, R) != L and R
-                    let new_sup = if let Some(new_sup) = self.ctx.min(&supe, maybe_super).either() {
+                    let new_super = if let Some(new_sup) = self.ctx.min(&supe, maybe_super).either()
+                    {
                         new_sup.clone()
                     } else {
                         self.ctx.intersection(&supe, maybe_super)
                     };
-                    self.sub_unify(&sub, &new_sup)?;
+                    if !maybe_sub.is_recursive() && (&sub != maybe_sub || &new_super != maybe_super)
+                    {
+                        self.sub_unify(&sub, &new_super)?;
+                    }
                     // ?T(:> Int, <: Int) ==> ?T == Int
                     // ?T(:> List(Int, 3), <: List(?T, ?N)) ==> ?T == List(Int, 3)
                     // ?T(:> List(Int, 3), <: Indexable(?K, ?V)) ==> ?T(:> List(Int, 3), <: Indexable(0..2, Int))
                     if !sub.is_refinement()
-                        && new_sup.qual_name() == sub.qual_name()
+                        && new_super.qual_name() == sub.qual_name()
-                        && !new_sup.is_unbound_var()
+                        && !new_super.is_unbound_var()
                         && !sub.is_unbound_var()
                     {
                         maybe_sub.link(&sub, self.undoable);
                     } else {
-                        maybe_sub.update_tyvar(sub, new_sup, self.undoable, true);
+                        maybe_sub.update_tyvar(sub, new_super, self.undoable, true);
                     }
                 }
                 // sub_unify(?T(: Type), Int): (?T(<: Int))

crates/erg_compiler/ty/mod.rs

@@ -31,7 +31,7 @@ use erg_common::fresh::FRESH_GEN;
 use erg_common::log;
 use erg_common::set::Set;
 use erg_common::traits::{LimitedDisplay, Locational, StructuralEq};
-use erg_common::{enum_unwrap, fmt_option, ref_addr_eq, set, set_recursion_limit, Str};
+use erg_common::{enum_unwrap, fmt_option, ref_addr_eq, set, Str};
 
 use erg_parser::ast::Expr;
 use erg_parser::token::TokenKind;
@@ -1005,7 +1005,7 @@ impl Eq for RefineKind {}
 /// {_: StrWithLen N | N >= 0}
 /// {T: (Int, Int) | T.0 >= 0, T.1 >= 0}
 /// ```
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone)]
 pub struct RefinementType {
     pub var: Str,
     pub t: Box<Type>,
@@ -1029,6 +1029,24 @@ impl<'a> TryFrom<&'a Type> for &'a RefinementType {
     }
 }
 
+impl PartialEq for RefinementType {
+    fn eq(&self, other: &Self) -> bool {
+        self.t == other.t && *self.pred == other.pred.clone().change_subject_name(self.var.clone())
+    }
+}
+
+impl Eq for RefinementType {}
+
+impl Hash for RefinementType {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.t.hash(state);
+        self.pred
+            .clone()
+            .change_subject_name("%RefinementType::hash".into())
+            .hash(state);
+    }
+}
+
 impl LimitedDisplay for RefinementType {
     fn limited_fmt<W: std::fmt::Write>(&self, f: &mut W, limit: isize) -> std::fmt::Result {
         if limit == 0 {
@@ -3616,8 +3634,6 @@ impl Type {
                 fv.crack().destructive_coerce();
             }
             Type::FreeVar(fv) if fv.is_unbound_and_sandwiched() => {
-                // TODO: other way to avoid infinite recursion
-                set_recursion_limit!({}, 128);
                 let (sub, _sup) = fv.get_subsup().unwrap();
                 sub.destructive_coerce();
                 self.destructive_link(&sub);
@@ -3684,7 +3700,6 @@ impl Type {
                 }
             }
             Type::FreeVar(fv) if fv.is_unbound_and_sandwiched() => {
-                set_recursion_limit!({}, 128);
                 let (sub, _sup) = fv.get_subsup().unwrap();
                 sub.undoable_coerce(list);
                 self.undoable_link(&sub, list);