impl Sentinel, part of #650 by asukaminato0721 · Pull Request #2252 · facebook/pyrefly

asukaminato0721 · 2026-01-29T03:53:33Z

Summary

Fixes part of #650

Added a sentinel literal type and wired is/is not narrowing to use final-name initializers, so Final sentinels now narrow even when the declared type isn’t literal. Updated literal display/output handling.

Test Plan

Added narrowing tests for Final bool and object sentinels.

Copilot

Pull request overview

This PR implements sentinel literal types to support type narrowing with is/is not operations on Final variables, as part of addressing issue #650 for comprehensive type guard support.

Changes:

Added LitSentinel variant to the Lit enum for representing sentinel values
Implemented final_sentinel_literal_for_expr to detect Final sentinel values and convert them to literal types
Integrated sentinel narrowing into is/is not narrowing operations
Updated type display and output handling for sentinel literals

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
`pyrefly/lib/test/narrow.rs`	Added test cases for Final bool and object sentinel narrowing
`pyrefly/lib/alt/narrow.rs`	Implemented sentinel detection and integrated into narrowing logic
`crates/pyrefly_types/src/literal.rs`	Added `LitSentinel` struct and related trait implementations
`crates/pyrefly_types/src/display.rs`	Added display formatting for sentinel literals
`crates/pyrefly_types/src/type_output.rs`	Added output handling for sentinel literals
`Cargo.lock`	Automatic checksum update for backtrace dependency

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Copilot · 2026-01-29T04:51:40Z

crates/pyrefly_types/src/literal.rs

+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Visit, VisitMut, TypeEq)]
+pub struct LitSentinel {
+    pub module: ModuleName,
+    pub name: Name,
+    pub range: Option<TextRange>,
+    pub class: ClassType,
+}
+
+impl Ord for LitSentinel {
+    fn cmp(&self, other: &Self) -> Ordering {
+        (&self.module, &self.name, &self.class).cmp(&(&other.module, &other.name, &other.class))
+    }
+}
+
+impl PartialOrd for LitSentinel {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}


The derived PartialEq, Eq, and Hash traits on line 71 compare/hash all fields including range, but the manual Ord and PartialOrd implementations exclude range from comparison. This is inconsistent and violates Rust's requirements:

Ord must be consistent with PartialEq: if two values are equal by cmp, they must be equal by PartialEq

Hash must be consistent with PartialEq: if two values are equal by PartialEq, they must have the same hash

Currently, two LitSentinel values that differ only in their range field would be:

Unequal by PartialEq (includes range)

Equal by Ord (excludes range)

Potentially different hashes (includes range)

This violates constraint 1. The fix is to manually implement PartialEq, Eq, and Hash to exclude range, matching the Ord behavior. See how similar types in the codebase handle this pattern.

yangdanny97

Hmm, I don't like adding a new literal case to represent a potentially non-literal type.

This is the implementation I have in mind:

at binding phase, if we see a is <some variable> we can generate a IsSentinel/IsNotSentinel narrow-op that holds 1) the variable binding idx and 2) the annotation idx
when that narrow op is solved it looks up the variable, looks up the annotation, and narrows the subject if the annotation is final. if it isn't final then we do nothing

.

github-actions · 2026-02-11T17:48:56Z

Diff from mypy_primer, showing the effect of this PR on open source code:

urllib3 (https://github.com/urllib3/urllib3)
- ERROR src/urllib3/util/timeout.py:128:16-79: Returned type `_TYPE_DEFAULT | float | None` is not assignable to declared return type `float | None` [bad-return]
- ERROR src/urllib3/util/timeout.py:150:19-24: Argument `_TYPE_DEFAULT | float` is not assignable to parameter `x` with type `Buffer | SupportsFloat | SupportsIndex | str` in function `float.__new__` [bad-argument-type]
- ERROR src/urllib3/util/timeout.py:158:16-26: `<=` is not supported between `_TYPE_DEFAULT` and `Literal[0]` [unsupported-operation]
- ERROR src/urllib3/util/timeout.py:270:24-34: Returned type `_TYPE_DEFAULT | float` is not assignable to declared return type `float | None` [bad-return]
- ERROR src/urllib3/util/timeout.py:271:30-84: No matching overload found for function `min` called with arguments: (float, _TYPE_DEFAULT | float) [no-matching-overload]
+ ERROR src/urllib3/util/timeout.py:271:23-85: No matching overload found for function `max` called with arguments: (Literal[0], float) [no-matching-overload]
- ERROR src/urllib3/util/timeout.py:271:31-71: `-` is not supported between `_TYPE_DEFAULT` and `float` [unsupported-operation]
- ERROR src/urllib3/util/timeout.py:273:27-67: `-` is not supported between `_TYPE_DEFAULT` and `float` [unsupported-operation]
- ::error file=src/urllib3/util/timeout.py,line=128,col=16,endLine=128,endColumn=79,title=Pyrefly bad-return::Returned type `_TYPE_DEFAULT | float | None` is not assignable to declared return type `float | None`
- ::error file=src/urllib3/util/timeout.py,line=150,col=19,endLine=150,endColumn=24,title=Pyrefly bad-argument-type::Argument `_TYPE_DEFAULT | float` is not assignable to parameter `x` with type `Buffer | SupportsFloat | SupportsIndex | str` in function `float.__new__`
- ::error file=src/urllib3/util/timeout.py,line=158,col=16,endLine=158,endColumn=26,title=Pyrefly unsupported-operation::`<=` is not supported between `_TYPE_DEFAULT` and `Literal[0]`%0A  Argument `_TYPE_DEFAULT` is not assignable to parameter `value` with type `int` in function `int.__ge__`
- ::error file=src/urllib3/util/timeout.py,line=270,col=24,endLine=270,endColumn=34,title=Pyrefly bad-return::Returned type `_TYPE_DEFAULT | float` is not assignable to declared return type `float | None`
- ::error file=src/urllib3/util/timeout.py,line=271,col=30,endLine=271,endColumn=84,title=Pyrefly no-matching-overload::No matching overload found for function `min` called with arguments: (float, _TYPE_DEFAULT | float)%0A  Possible overloads:%0A  (arg1: SupportsRichComparisonT, arg2: SupportsRichComparisonT, /, *_args: SupportsRichComparisonT, *, key: None = None) -> SupportsRichComparisonT [closest match]%0A  (arg1: _T, arg2: _T, /, *_args: _T, *, key: (_T) -> SupportsRichComparison) -> _T%0A  (iterable: Iterable[SupportsRichComparisonT], /, *, key: None = None) -> SupportsRichComparisonT%0A  (iterable: Iterable[_T], /, *, key: (_T) -> SupportsRichComparison) -> _T%0A  (iterable: Iterable[SupportsRichComparisonT], /, *, key: None = None, default: _T) -> SupportsRichComparisonT | _T%0A  (iterable: Iterable[_T1], /, *, key: (_T1) -> SupportsRichComparison, default: _T2) -> _T1 | _T2
+ ::error file=src/urllib3/util/timeout.py,line=271,col=23,endLine=271,endColumn=85,title=Pyrefly no-matching-overload::No matching overload found for function `max` called with arguments: (Literal[0], float)%0A  Possible overloads:%0A  (arg1: SupportsRichComparisonT, arg2: SupportsRichComparisonT, /, *_args: SupportsRichComparisonT, *, key: None = None) -> SupportsRichComparisonT [closest match]%0A  (arg1: _T, arg2: _T, /, *_args: _T, *, key: (_T) -> SupportsRichComparison) -> _T%0A  (iterable: Iterable[SupportsRichComparisonT], /, *, key: None = None) -> SupportsRichComparisonT%0A  (iterable: Iterable[_T], /, *, key: (_T) -> SupportsRichComparison) -> _T%0A  (iterable: Iterable[SupportsRichComparisonT], /, *, key: None = None, default: _T) -> SupportsRichComparisonT | _T%0A  (iterable: Iterable[_T1], /, *, key: (_T1) -> SupportsRichComparison, default: _T2) -> _T1 | _T2
- ::error file=src/urllib3/util/timeout.py,line=271,col=31,endLine=271,endColumn=71,title=Pyrefly unsupported-operation::`-` is not supported between `_TYPE_DEFAULT` and `float`%0A  Argument `_TYPE_DEFAULT` is not assignable to parameter `value` with type `float` in function `float.__rsub__`
- ::error file=src/urllib3/util/timeout.py,line=273,col=27,endLine=273,endColumn=67,title=Pyrefly unsupported-operation::`-` is not supported between `_TYPE_DEFAULT` and `float`%0A  Argument `_TYPE_DEFAULT` is not assignable to parameter `value` with type `float` in function `float.__rsub__`

sphinx (https://github.com/sphinx-doc/sphinx)
- ERROR sphinx/theming.py:542:65-81: Object of class `EllipsisType` has no attribute `split` [missing-attribute]
- ERROR sphinx/theming.py:550:62-75: Object of class `EllipsisType` has no attribute `split` [missing-attribute]
+ ERROR sphinx/theming.py:542:53-87: No matching overload found for function `map.__new__` called with arguments: (type[map[_S]], Overload[
+   (self: LiteralString, chars: LiteralString | None = None, /) -> LiteralString
+   (self: str, chars: str | None = None, /) -> str
+ ], list[str] | Unknown) [no-matching-overload]
+ ERROR sphinx/theming.py:550:50-81: No matching overload found for function `map.__new__` called with arguments: (type[map[_S]], Overload[
+   (self: LiteralString, chars: LiteralString | None = None, /) -> LiteralString
+   (self: str, chars: str | None = None, /) -> str
+ ], list[str] | Unknown) [no-matching-overload]
- ::error file=sphinx/theming.py,line=542,col=65,endLine=542,endColumn=81,title=Pyrefly missing-attribute::Object of class `EllipsisType` has no attribute `split`
- ::error file=sphinx/theming.py,line=550,col=62,endLine=550,endColumn=75,title=Pyrefly missing-attribute::Object of class `EllipsisType` has no attribute `split`
+ ::error file=sphinx/theming.py,line=542,col=53,endLine=542,endColumn=87,title=Pyrefly no-matching-overload::No matching overload found for function `map.__new__` called with arguments: (type[map[_S]], Overload[%0A  (self: LiteralString, chars: LiteralString | None = None, /) -> LiteralString%0A  (self: str, chars: str | None = None, /) -> str%0A], list[str] | Unknown)%0A  Possible overloads:%0A  (cls: type[map[_S]], func: (_T1) -> _S, iterable: Iterable[_T1], /) -> map[_S] [closest match]%0A  (cls: type[map[_S]], func: (_T1, _T2) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], /) -> map[_S]%0A  (cls: type[map[_S]], func: (_T1, _T2, _T3) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], /) -> map[_S]%0A  (cls: type[map[_S]], func: (_T1, _T2, _T3, _T4) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], iter4: Iterable[_T4], /) -> map[_S]%0A  (cls: type[map[_S]], func: (_T1, _T2, _T3, _T4, _T5) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], iter4: Iterable[_T4], iter5: Iterable[_T5], /) -> map[_S]%0A  (cls: type[map[_S]], func: (...) -> _S, iterable: Iterable[Any], iter2: Iterable[Any], iter3: Iterable[Any], iter4: Iterable[Any], iter5: Iterable[Any], iter6: Iterable[Any], /, *iterables: Iterable[Any]) -> map[_S]
+ ::error file=sphinx/theming.py,line=550,col=50,endLine=550,endColumn=81,title=Pyrefly no-matching-overload::No matching overload found for function `map.__new__` called with arguments: (type[map[_S]], Overload[%0A  (self: LiteralString, chars: LiteralString | None = None, /) -> LiteralString%0A  (self: str, chars: str | None = None, /) -> str%0A], list[str] | Unknown)%0A  Possible overloads:%0A  (cls: type[map[_S]], func: (_T1) -> _S, iterable: Iterable[_T1], /) -> map[_S] [closest match]%0A  (cls: type[map[_S]], func: (_T1, _T2) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], /) -> map[_S]%0A  (cls: type[map[_S]], func: (_T1, _T2, _T3) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], /) -> map[_S]%0A  (cls: type[map[_S]], func: (_T1, _T2, _T3, _T4) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], iter4: Iterable[_T4], /) -> map[_S]%0A  (cls: type[map[_S]], func: (_T1, _T2, _T3, _T4, _T5) -> _S, iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], iter4: Iterable[_T4], iter5: Iterable[_T5], /) -> map[_S]%0A  (cls: type[map[_S]], func: (...) -> _S, iterable: Iterable[Any], iter2: Iterable[Any], iter3: Iterable[Any], iter4: Iterable[Any], iter5: Iterable[Any], iter6: Iterable[Any], /, *iterables: Iterable[Any]) -> map[_S]

meta-codesync · 2026-02-23T16:09:33Z

@yangdanny97 has imported this pull request. If you are a Meta employee, you can view this in D94090300.

yangdanny97 · 2026-02-25T22:34:08Z

There's a potential performance regression here, I'll investigate when I have time.

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asukaminato0721 marked this pull request as ready for review January 29, 2026 04:48

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asukaminato0721 mentioned this pull request Jan 29, 2026

impl type guard for Ellipsis #650 #2253

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connernilsen requested a review from yangdanny97 February 4, 2026 19:41

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asukaminato0721 force-pushed the 650 branch from c603369 to 455bfed Compare February 9, 2026 04:40

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asukaminato0721 force-pushed the 650 branch from 366bb54 to 455bfed Compare February 9, 2026 05:29

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asukaminato0721 added 3 commits February 12, 2026 02:33

impl Sentinel

624b6f3

.

update

0ebbd86

.

8301a2e

asukaminato0721 force-pushed the 650 branch from 345ebb3 to 8301a2e Compare February 11, 2026 17:35

asukaminato0721 requested a review from yangdanny97 February 11, 2026 17:55

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impl Sentinel, part of #650#2252

impl Sentinel, part of #650#2252
asukaminato0721 wants to merge 3 commits intofacebook:mainfrom
asukaminato0721:650

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asukaminato0721 commented Jan 29, 2026

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