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Narrowing a backed enum by its ->value comparison

Group: Cross-analyzer regressions · Category: regression · File: regressions_backed_enum_value_narrowing.php

A backed enum's case↔value map is a bijection, so $s->value === 'H' uniquely selects Suit::Hearts, and the fall-through is Suit::Spades. The match ($s) that follows is therefore exhaustive with only the Suit::Spades arm. Analyzers diverge on whether they propagate a ->value comparison to the enum case. PHPStan narrows case identity ($s === Suit::Hearts) but not the ->value form, so it keeps the full Suit type and reports the match as non-exhaustive. Source lead: cross-tool narrowing probe (companion to the class-string case).

Analyzer results

AnalyzerVersionResultDiagnostics
phan 6.0.10Phan 6.0.10 php-ast version 1.1.3 PHP version used to run Phan: 8.5.11 Fail

No diagnostics reported.

Expectation diff
Line 40: Expected 1 error(s)
phpstan 2.3.1PHPStan - PHP Static Analysis Tool 2.3.1 Pass reported Lv.4+ 
regressions_backed_enum_value_narrowing.php:33: Match expression does not handle remaining value: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts [reported-from-level=4]
regressions_backed_enum_value_narrowing.php:40: Match expression does not handle remaining value: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts [reported-from-level=4]
With strict-rules
regressions_backed_enum_value_narrowing.php:33: Match expression does not handle remaining value: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts
regressions_backed_enum_value_narrowing.php:40: Match expression does not handle remaining value: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts
psalm 6.20.0Psalm 6.20.0@804f03c0c183d149fcd4b8c7c0c9b3fbf836d34c
next: 7.0.0-rc2		 Pass 
regressions_backed_enum_value_narrowing.php:33: This match expression is not exhaustive - consider values enum(Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts) [UnhandledMatchCondition]
regressions_backed_enum_value_narrowing.php:40: This match expression is not exhaustive - consider values enum(Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts) [UnhandledMatchCondition]
mago 1.57.0mago 1.57.0 Pass 
regressions_backed_enum_value_narrowing.php:33: Non-exhaustive `match` expression: subject of type `enum(Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit)` is not fully handled. [match-not-exhaustive]
regressions_backed_enum_value_narrowing.php:40: Non-exhaustive `match` expression: subject of type `enum(Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit)` is not fully handled. [match-not-exhaustive]
mir 0.87.0mir 0.87.0 Pass 
regressions_backed_enum_value_narrowing.php:40: UnhandledMatchCondition: Unhandled match condition: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts [MIR0405]
phpantom 0.11.1phpantom_lsp 0.11.1 Fail

No diagnostics reported.

Expectation diff
Line 40: Expected 1 error(s)
intelephense 1.18.5intelephense 1.18.5 Fail

No diagnostics reported.

Expectation diff
Line 40: Expected 1 error(s)
phpactor 2026.10.07.0Phpactor 2026.10.07.0 Fail

No diagnostics reported.

Expectation diff
Line 40: Expected 1 error(s)
phpy 1.0.19409phpy 1.0.19409 Fail

No diagnostics reported.

Expectation diff
Line 40: Expected 1 error(s)
qodana 262.10968.76PhpStorm 262.10968.76 Pass 
regressions_backed_enum_value_narrowing.php:33: 'match' expression has uncovered enum cases [PhpUncoveredEnumCasesInspection]
regressions_backed_enum_value_narrowing.php:40: 'match' expression has uncovered enum cases [PhpUncoveredEnumCasesInspection]
noverify 0.5.5NoVerify, version 0.5.5: built on: 2025.04.22 14:36:46 OS: r-kuchinskas arm64 Commit: 4774b82f8adc53fbef38f95e97af4b953b4d1529 Fail 
regressions_backed_enum_value_narrowing.php:27: Class or interface named \Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit does not exist [undefinedClass]
regressions_backed_enum_value_narrowing.php:29: Property {\Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit}->value does not exist [undefinedProperty]
regressions_backed_enum_value_narrowing.php:34: Class constant \Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Spades does not exist [undefinedConstant]
regressions_backed_enum_value_narrowing.php:38: Class or interface named \Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit does not exist [undefinedClass]
regressions_backed_enum_value_narrowing.php:41: Class constant \Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Spades does not exist [undefinedConstant]
Expectation diff
Line 40: Expected 1 error(s)
steins 0.1.8steins 0.1.8 (2026-09-21 revision 76306a9) Fail

No diagnostics reported.

Expectation diff
Line 40: Expected 1 error(s)
phpstan-strict 2.3.1PHPStan - PHP Static Analysis Tool 2.3.1 Pass 
regressions_backed_enum_value_narrowing.php:33: Match expression does not handle remaining value: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts
regressions_backed_enum_value_narrowing.php:40: Match expression does not handle remaining value: Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts
psalm-next 7.0.0-rc2Psalm 7.0.0-rc2@20339e3fe5b8d03bcd8061030eb2a83ad50e5783 Pass 
regressions_backed_enum_value_narrowing.php:33: This match expression is not exhaustive - consider values enum(Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts) [UnhandledMatchCondition]
regressions_backed_enum_value_narrowing.php:40: This match expression is not exhaustive - consider values enum(Conformance\Tests\RegressionsBackedEnumValueNarrowing\Suit::Hearts) [UnhandledMatchCondition]

Source

<?php

declare(strict_types=1);

namespace Conformance\Tests\RegressionsBackedEnumValueNarrowing;

/**
 * Narrowing a backed enum by its `->value` comparison.
 *
 * A backed enum's case↔value map is a bijection, so `$s->value === 'H'` uniquely selects
 * `Suit::Hearts`, and the fall-through is `Suit::Spades`. The `match ($s)` that follows is
 * therefore exhaustive with only the `Suit::Spades` arm.
 *
 * Analyzers diverge on whether they propagate a `->value` comparison to the enum case.
 * PHPStan narrows case identity (`$s === Suit::Hearts`) but not the `->value` form, so it
 * keeps the full `Suit` type and reports the `match` as non-exhaustive.
 *
 * Source lead: cross-tool narrowing probe (companion to the class-string case).
 */

enum Suit: string
{
    case Hearts = 'H';
    case Spades = 'S';
}

function describe(Suit $s): string // E<noverify>: NoVerify 0.5.5 does not support enums and treats Suit as an undefined class
{
    if ($s->value === 'H') { // E<noverify>: enum property ->value unresolved because enums are unsupported
        return 'hearts';
    }

    return match ($s) { // E<phpstan>: $s not narrowed by ->value === 'H', so match is seen as non-exhaustive (Suit::Hearts unhandled) // E<phpstan-strict>: same // E<psalm>: UnhandledMatchCondition // E<mago>: match-not-exhaustive // E<pzoom>: same UnhandledMatchCondition as Psalm // E<qodana>: PhpUncoveredEnumCasesInspection. Phan is silent on the unguarded match too, so it never checked exhaustiveness
        Suit::Spades => 'spades', // E<noverify>: enum case constant Suit::Spades unresolved
    };
}

function stillFullSuit(Suit $s): string // E<noverify>: Suit unresolved, same as describe()
{
    return match ($s) { // E: Hearts is unhandled unless ->value already narrowed the subject
        Suit::Spades => 'spades', // E<noverify>: enum case constant unresolved
    };
}