Major fixes and new features

venv/lib/python3.12/site-packages/mypy/mro.py

@@ -0,0 +1,62 @@
+from __future__ import annotations
+
+from typing import Callable
+
+from mypy.nodes import TypeInfo
+from mypy.types import Instance
+from mypy.typestate import type_state
+
+
+def calculate_mro(info: TypeInfo, obj_type: Callable[[], Instance] | None = None) -> None:
+    """Calculate and set mro (method resolution order).
+
+    Raise MroError if cannot determine mro.
+    """
+    mro = linearize_hierarchy(info, obj_type)
+    assert mro, f"Could not produce a MRO at all for {info}"
+    info.mro = mro
+    # The property of falling back to Any is inherited.
+    info.fallback_to_any = any(baseinfo.fallback_to_any for baseinfo in info.mro)
+    type_state.reset_all_subtype_caches_for(info)
+
+
+class MroError(Exception):
+    """Raised if a consistent mro cannot be determined for a class."""
+
+
+def linearize_hierarchy(
+    info: TypeInfo, obj_type: Callable[[], Instance] | None = None
+) -> list[TypeInfo]:
+    # TODO describe
+    if info.mro:
+        return info.mro
+    bases = info.direct_base_classes()
+    if not bases and info.fullname != "builtins.object" and obj_type is not None:
+        # Probably an error, add a dummy `object` base class,
+        # otherwise MRO calculation may spuriously fail.
+        bases = [obj_type().type]
+    lin_bases = []
+    for base in bases:
+        assert base is not None, f"Cannot linearize bases for {info.fullname} {bases}"
+        lin_bases.append(linearize_hierarchy(base, obj_type))
+    lin_bases.append(bases)
+    return [info] + merge(lin_bases)
+
+
+def merge(seqs: list[list[TypeInfo]]) -> list[TypeInfo]:
+    seqs = [s.copy() for s in seqs]
+    result: list[TypeInfo] = []
+    while True:
+        seqs = [s for s in seqs if s]
+        if not seqs:
+            return result
+        for seq in seqs:
+            head = seq[0]
+            if not [s for s in seqs if head in s[1:]]:
+                break
+        else:
+            raise MroError()
+        result.append(head)
+        for s in seqs:
+            if s[0] is head:
+                del s[0]