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