fix(name-resolve): Fix Scope.__eq__ giving recursion errors

Author: MarcellPerger1

parser/typecheck/typecheck.py

@@ -2,6 +2,7 @@
 
 from dataclasses import dataclass, field
 
+from util.recursive_eq import recursive_eq
 from ..astgen.ast_node import (
     AstNode, walk_ast, AstIdent, AstDeclNode, AstDefine, VarDeclType,
     VarDeclScope, FilteredWalker)
@@ -84,6 +85,9 @@ class Scope:
     (so type codegen/type-checker knows what each AstIdent refers to)"""
 
 
+Scope.__eq__ = recursive_eq(Scope.__eq__)
+
+
 class NameResolutionError(BaseLocatedError):
     pass
 

util/recursive_eq.py

@@ -0,0 +1,26 @@
+"""Safe recursive equality comparison."""
+import functools
+
+
+def recursive_eq(fn):
+    """Must be used as decorator, like reprlib.recursive_repr.
+    Works by hypothesising that 2 ids are equal. Then, it tries to compare
+    them. If it encounters one of them again, it checks that the corresponding
+    value is the hypothesised value. If so, they're equal. If not, they're
+    unequal."""
+    hypotheses: dict[int, int] = {}  # int <-> int (should be undirected)
+
+    @functools.wraps(fn)
+    def eq(a, b):
+        if (bid_exp := hypotheses.get(id(a))) is not None:
+            return bid_exp == id(b)
+        if (aid_exp := hypotheses.get(id(b))) is not None:
+            return aid_exp == id(a)
+        hypotheses[id(a)] = id(b)
+        hypotheses[id(b)] = id(a)
+        try:
+            return fn(a, b)  # Will call this function again
+        finally:
+            del hypotheses[id(a)]
+            del hypotheses[id(b)]
+    return eq