POC - Allow short ternary for false

src/Rules/DisallowedConstructs/DisallowedShortTernaryRule.php

@@ -7,6 +7,10 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\Constant\ConstantBooleanType;
+use PHPStan\Type\StaticTypeFactory;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
 
 /**
  * @implements Rule<Ternary>
@@ -25,11 +29,29 @@
 			return [];
 		}
 
+		if ($scope->getType($node->cond)->isSuperTypeOf($this->getNonBooleanFalseyType())->no()) {
+			return [];
+		}
+
 		return [
 			RuleErrorBuilder::message('Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.')
 				->identifier('ternary.shortNotAllowed')
 				->build(),
 		];
 	}
 
+	private function getNonBooleanFalseyType(): Type
+	{
+		static $falseyWithoutFalse;
+
+		if ($falseyWithoutFalse === null) {
+			$falseyWithoutFalse = TypeCombinator::remove(
+				StaticTypeFactory::falsey(),
+				new ConstantBooleanType(false),
+			);
+		}
+
+		return $falseyWithoutFalse;
+	}
+
 }

tests/Rules/DisallowedConstructs/DisallowedShortTernaryRuleTest.php

@@ -21,11 +21,43 @@ public function testRule(): void
 		$this->analyse([__DIR__ . '/data/short-ternary.php'], [
 			[
 				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
-				3,
+				6,
 			],
 			[
 				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
-				4,
+				7,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				13,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				14,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				31,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				32,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				37,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				38,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				49,
+			],
+			[
+				'Short ternary operator is not allowed. Use null coalesce operator if applicable or consider using long ternary.',
+				50,
 			],
 		]);
 	}

tests/Rules/DisallowedConstructs/data/short-ternary.php

@@ -1,5 +1,56 @@
 <?php
 
-$foo = 123 ?: 456;
-$bar = 123 ? : 456;
-$baz = 123 ? 456 : 789;
+/** @var int $cond */
+$cond = 123;
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+$baz = $cond ? 456 : 789;
+
+/** @var int|false $cond */
+$cond = 123;
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var positive-int|false $ */
+$cond = 123;
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var object|false $ */
+$cond = 123;
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var string|false $ */
+$cond = '123';
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var non-empty-string|false $ */
+$cond = '123';
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var non-falsy-string|false $ */
+$cond = '123';
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var array|false $ */
+$cond = [123];
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;
+
+/** @var non-empty-array|false $ */
+$cond = [123];
+
+$foo = $cond ?: 456;
+$bar = $cond ? : 456;