ArrayUnionDropsRightValues

warning native off by default

Group: Probable bugs

Array union keeps left-hand values when keys collide. Use merging when both lists must contribute their values. This inspection is disabled by default because the intended policy or use can vary.

Example

<?php
$all=[10,20]+[30,40]; foreach($all as $v){echo $v;}

Reported:

• line 2: Use array merging to preserve the right-hand list values.

Detection

• Both operands of array union are nonempty literal arrays with implicit zero-based keys, and at least one right key collides. The result is subsequently iterated as a value list without key access; opt-in because first-value precedence can be intentional.
• The initial supported downstream proof is an immediately following by-value foreach without a key binding.
• Resolve builtin functions, classes, constants and methods; user-defined lookalikes are excluded. Follow only bounded local proof in one lexical scope.
• Emit one finding per violating operation, not per supporting evidence statement. When the proof is inconclusive, nothing is reported.

Exceptions (no report)

• Do not report unresolved or shadowed builtin names, unknown values, or incomplete receiver/type provenance. Unknown calls, aliases escaping, and intervening writes invalidate local proof. Similar code outside the stated detection contract is not a finding.
• Both standard suppression forms suppress this native ID.

Fix

None. Choosing a repair requires intent or additional runtime information.

PHP versions

Available throughout supported PHP 5.3–8.5 where the referenced builtin/extension is available. Respect syntax/version-specific receiver contracts; unavailable APIs are not this rule’s concern.

Configure

In custos.json:

{
  "rules": {
    "ArrayUnionDropsRightValues": {
      "enabled": true
    }
  }
}

Suppress

Before the statement or declaration (or the first statement of the file):

// @custos-ignore ArrayUnionDropsRightValues