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- 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]
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