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Description
Description
Summary
When multiple traits define properties with identical signatures but different attributes, PHP silently drops attributes during trait composition without any notice or warning.
Affected versions: PHP 8.0+ (since attributes were introduced)
Problem Description
PHP's trait system correctly handles method conflicts by throwing fatal errors when methods with the same name exist in multiple traits. However, when properties with identical signatures but different attributes are defined in multiple traits, PHP:
- ✅ Correctly merges the property (no fatal error)
- ❌ Silently drops attributes from one of the traits
- ❌ Provides no indication that attributes were lost
- ❌ Behavior is unpredictable (depends on trait order)
This creates silent data loss where code appears correct but attributes are missing.
Expected Behavior
When trait properties have identical signatures but different attributes, PHP should at minimum emit a notice or warning:
Notice: Trait property 'propertyName' has conflicting attributes during trait composition in %s on line %d
Reproduction Code
<?php
#[Attribute]
class Column {}
#[Attribute]
class Version {}
// Trait 1: Property with Column attribute
trait BasicTrait {
#[Column]
private ?string $data = null;
}
// Trait 2: Same property with Column AND Version attributes
trait VersionedTrait {
#[Column]
#[Version]
private ?string $data = null;
}
class TestEntity {
use BasicTrait;
use VersionedTrait; // Version attribute should be preserved
}
// Check what actually happened
$reflection = new ReflectionClass(TestEntity::class);
$property = $reflection->getProperty('data');
$attributes = $property->getAttributes();
echo "Total attributes: " . count($attributes) . "\n";
foreach ($attributes as $attr) {
echo "- " . $attr->getName() . "\n";
}
$versionAttrs = $property->getAttributes(Version::class);
echo "Version attributes: " . count($versionAttrs) . "\n";
if (count($versionAttrs) === 0) {
echo "BUG: Version attribute silently dropped!\n";
}
Expected Output
Notice: Trait property 'data' has conflicting attributes during trait composition in %s on line %d
Total attributes: 1
- Column
Version attributes: 0
BUG: Version attribute silently dropped!
Actual Output
Total attributes: 1
- Column
Version attributes: 0
BUG: Version attribute silently dropped!
Why This Is a Bug
- Inconsistent: Method conflicts properly throw fatal errors
- Silent data loss: PHP usually warns about potential issues
- Unpredictable: Same code behaves differently based on trait order
- No workaround: Cannot use
insteadof
oras
with properties
Proposed Fix
Emit a notice/warning when attributes are dropped during trait property merging (minimum viable fix).
PHP Version
PHP 8.2.28 (cli) (built: Mar 11 2025 17:58:12) (NTS)
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Operating System
No response