Improve Step 5 of overload call evaluation.#2250
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rchen152 wants to merge 7 commits intopython:mainfrom
Open
Improve Step 5 of overload call evaluation.#2250rchen152 wants to merge 7 commits intopython:mainfrom
rchen152 wants to merge 7 commits intopython:mainfrom
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Makes two modifications to step 5 of overload call evaluation: 1. When materializing arguments to check whether we can eliminate overloads, skip arguments that have the same parameter type in all overloads. 2. When we still have multiple overloads after the materialization filter, try to find a return type that all materializations of all other return types are assignable to. Updates the conformance tests as well. All type checkers already do (1). Mypy and pyrefly pass the conformance test for (2). I believe mypy has a heuristic that approximates the new rule; pyrefly implements it exactly.
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I think it's preferable to keep PRs updating type-checker versions separate from PRs implementing conformance suite and spec changes. |
docs/spec/overload.rst
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| - All possible :term:`materializations <materialize>` of the argument's type are | ||
| assignable to the corresponding parameter type, or | ||
| - The parameter types corresponding to this argument in all of the remaining overloads | ||
| are :term:`equivalent`. |
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I think this is correct but there's some subtlety in the wording that we should cover in the test cases:
- "The parameter types corresponding to this argument". That may be a very different parameter in each of the overloads; e.g. maybe one takes
*argsand the other has explicit arguments. So my reading is that to check this, you have to create for each overload a mapping between argument and parameter type, and consult that. What is the parameter type corresponding to an unpacked argument, though? - "the remaining overloads". So we only check this overload and all following overloads, not ones above it?
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Great points, thanks!
- I added a clarification about unpacked arguments and some more tests.
- Ah, I meant all of the candidate overloads that are remaining at the beginning of Step 5, not just the overloads following the one that we're checking. I replaced "remaining overloads" with "candidate overloads" - hopefully that's clearer.
carljm
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Apr 8, 2026
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Point taken, sorry! I was being a bit sloppy because I didn't want to open two PRs XD Version update here: #2254 |
* "remaining" overloads => "candidate" overloads * moar tests
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Thanks for the feedback! I believe I've addressed all the comments. |
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Makes two modifications to step 5 of overload call evaluation:
Updates the conformance tests as well. All type checkers already do (1). Mypy and pyrefly pass the conformance test for (2). I believe mypy has a heuristic that approximates the new rule; pyrefly implements it exactly.