[mypyc] feat: call native __len__ when defined

mypyc/irbuild/ll_builder.py

@@ -2444,7 +2444,15 @@ def builtin_len(self, val: Value, line: int, use_pyssize_t: bool = False) -> Val
         if isinstance(typ, RInstance):
             # TODO: Support use_pyssize_t
             assert not use_pyssize_t
-            length = self.gen_method_call(val, "__len__", [], int_rprimitive, line)
+
+            if typ.class_ir.has_method("__len__") and typ.class_ir.is_method_final("__len__"):
+                # Direct C call for final native __len__ methods
+                decl = typ.class_ir.method_decl("__len__")
+                length = self.call(decl, [val], [ARG_POS], [None], line)
+            else:
+                # Fallback: generic method call for non-native or ambiguous cases
+                length = self.gen_method_call(val, "__len__", [], int_rprimitive, line)
+
             length = self.coerce(length, int_rprimitive, line)
             ok, fail = BasicBlock(), BasicBlock()
             cond = self.binary_op(length, Integer(0), ">=", line)

mypyc/test-data/irbuild-dunders.test

@@ -1,24 +1,92 @@
 # Test cases for (some) dunder methods
 
 [case testDundersLen]
+from typing import final
+
 class C:
     def __len__(self) -> int:
         return 2
-
+@final
+class D:
+    def __len__(self) -> int:
+        return 2
+class E:
+    @final
+    def __len__(self) -> int:
+        return 2
+class F(C):
+    """def __len__(self) -> int:
+        return 3"""
 def f(c: C) -> int:
     return len(c)
+def g(d: D) -> int:
+    return len(d)
+def h(e: E) -> int:
+    return len(e)
+def i(f: F) -> int:
+    return len(f)
 [out]
 def C.__len__(self):
     self :: __main__.C
 L0:
     return 4
+def D.__len__(self):
+    self :: __main__.D
+L0:
+    return 4
+def E.__len__(self):
+    self :: __main__.E
+L0:
+    return 4
 def f(c):
     c :: __main__.C
     r0 :: int
     r1 :: bit
     r2 :: bool
 L0:
-    r0 = c.__len__()
+    r0 = C.__len__(c)
+    r1 = int_ge r0, 0
+    if r1 goto L2 else goto L1 :: bool
+L1:
+    r2 = raise ValueError('__len__() should return >= 0')
+    unreachable
+L2:
+    return r0
+def g(d):
+    d :: __main__.D
+    r0 :: int
+    r1 :: bit
+    r2 :: bool
+L0:
+    r0 = D.__len__(d)
+    r1 = int_ge r0, 0
+    if r1 goto L2 else goto L1 :: bool
+L1:
+    r2 = raise ValueError('__len__() should return >= 0')
+    unreachable
+L2:
+    return r0
+def h(e):
+    e :: __main__.E
+    r0 :: int
+    r1 :: bit
+    r2 :: bool
+L0:
+    r0 = E.__len__(e)
+    r1 = int_ge r0, 0
+    if r1 goto L2 else goto L1 :: bool
+L1:
+    r2 = raise ValueError('__len__() should return >= 0')
+    unreachable
+L2:
+    return r0
+def i(f):
+    f :: __main__.F
+    r0 :: int
+    r1 :: bit
+    r2 :: bool
+L0:
+    r0 = C.__len__(f)
     r1 = int_ge r0, 0
     if r1 goto L2 else goto L1 :: bool
 L1: