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Fix phpstan/phpstan#9634: Cannot use "T is never" in conditional return #5082

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Merged
VincentLanglet merged 4 commits into from
Mar 29, 2026
Merged

Fix phpstan/phpstan#9634: Cannot use "T is never" in conditional return #5082

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42c3d05
Fix "T is never" in conditional return type reported as always false
github-actions[bot] Feb 27, 2026
db3018b
Use nsrt/bug-9634 in MethodConditionalReturnTypeRuleTest and delete d…
phpstan-bot Mar 28, 2026
4e894ee
Add test for phpstan/phpstan#10938: check if Iterator is empty via never
phpstan-bot Mar 28, 2026
72952cb
Add unit tests for NeverType and NonAcceptingNeverType isSuperTypeOf …
phpstan-bot Mar 28, 2026
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5 changes: 5 additions & 0 deletions src/Type/NeverType.php
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
use PHPStan\ShouldNotHappenException;
use PHPStan\TrinaryLogic;
use PHPStan\Type\Enum\EnumCaseObjectType;
use PHPStan\Type\Generic\TemplateType;
use PHPStan\Type\Traits\NonGeneralizableTypeTrait;
use PHPStan\Type\Traits\NonGenericTypeTrait;
use PHPStan\Type\Traits\NonRemoveableTypeTrait;
Expand Down Expand Up @@ -81,6 +82,10 @@ public function isSuperTypeOf(Type $type): IsSuperTypeOfResult
return IsSuperTypeOfResult::createYes();
}

if ($type instanceof TemplateType) {
return IsSuperTypeOfResult::createMaybe();
}

return IsSuperTypeOfResult::createNo();
}

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6 changes: 6 additions & 0 deletions src/Type/NonAcceptingNeverType.php
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Expand Up @@ -2,6 +2,8 @@

namespace PHPStan\Type;

use PHPStan\Type\Generic\TemplateType;

/** @api */
class NonAcceptingNeverType extends NeverType
{
Expand All @@ -21,6 +23,10 @@ public function isSuperTypeOf(Type $type): IsSuperTypeOfResult
return IsSuperTypeOfResult::createMaybe();
}

if ($type instanceof TemplateType) {
return IsSuperTypeOfResult::createMaybe();
}

return IsSuperTypeOfResult::createNo();
}

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28 changes: 28 additions & 0 deletions tests/PHPStan/Analyser/nsrt/bug-10938.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
<?php declare(strict_types = 1);

namespace Bug10938;

use function PHPStan\Testing\assertType;

/**
* @template TKey
* @template TValue
* @extends \IteratorAggregate<TKey, TValue>
*/
interface Collection extends \IteratorAggregate
{
/**
* @return (TValue is never ? true : bool)
*/
function isEmpty(): bool;
}

/** @param Collection<never, never> $c */
function emptyCollection(Collection $c): void {
assertType('true', $c->isEmpty());
}

/** @param Collection<int, string> $c */
function nonEmptyCollection(Collection $c): void {
assertType('bool', $c->isEmpty());
}
29 changes: 29 additions & 0 deletions tests/PHPStan/Analyser/nsrt/bug-9634.php
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@@ -0,0 +1,29 @@
<?php declare(strict_types = 1);

namespace Bug9634;

use function PHPStan\Testing\assertType;

/** @template T */
interface Option {
/** @return self<never> */
static function none(): self;

/** @return T */
function unwrap(): mixed;

/**
* @return (T is never ? false : bool)
*/
function isSome(): bool;
}

/** @param Option<never> $o */
function f(Option $o): void {
assertType('false', $o->isSome());
}

/** @param Option<int> $o */
function g(Option $o): void {
assertType('bool', $o->isSome());
}
10 changes: 10 additions & 0 deletions tests/PHPStan/Rules/PhpDoc/MethodConditionalReturnTypeRuleTest.php
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Expand Up @@ -102,4 +102,14 @@ public function testBug11939(): void
$this->analyse([__DIR__ . '/data/bug-11939.php'], []);
}

public function testBug9634(): void
{
$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-9634.php'], []);
}

public function testBug10938(): void
{
$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-10938.php'], []);
}

}
24 changes: 24 additions & 0 deletions tests/PHPStan/Type/TemplateTypeTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -281,6 +281,30 @@ public static function dataIsSuperTypeOf(): array
TrinaryLogic::createMaybe(),
TrinaryLogic::createYes(),
],
23 => [
$templateType('T', null),
new NeverType(),
TrinaryLogic::createYes(), // T isSuperTypeTo *NEVER* - never is bottom type
TrinaryLogic::createMaybe(), // *NEVER* isSuperTypeTo T - T could be never
],
24 => [
$templateType('T', null),
new NonAcceptingNeverType(),
TrinaryLogic::createYes(), // T isSuperTypeTo never - never is bottom type
TrinaryLogic::createMaybe(), // never isSuperTypeTo T - T could be never
],
25 => [
$templateType('T', new ObjectType('DateTime')),
new NeverType(),
TrinaryLogic::createYes(), // (T of DateTime) isSuperTypeTo *NEVER* - never is bottom type
TrinaryLogic::createMaybe(), // *NEVER* isSuperTypeTo (T of DateTime) - T could be never
],
26 => [
$templateType('T', new ObjectType('DateTime')),
new NonAcceptingNeverType(),
TrinaryLogic::createYes(), // (T of DateTime) isSuperTypeTo never - never is bottom type
TrinaryLogic::createMaybe(), // never isSuperTypeTo (T of DateTime) - T could be never
],
];
}

Expand Down
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