ArrayColumnDuplicateIndexLoss

warning native on by default

Group: Probable bugs

Using duplicate index values in array_column overwrites earlier rows. Use unique indices or group rows when every value must remain available.

Example

<?php
$a=array_column([["id"=>7,"v"=>"a"],["id"=>7,"v"=>"b"]],"v","id");

Reported:

• line 2: Use unique index values or group the duplicate rows.

Detection

• Resolved array_column receives a literal array of literal rows, a literal column key, and a literal index key whose normalized array-key values repeat in two rows. Both rows contain the requested column.
• Evaluate the effective array after PHP key normalization and duplicate-key overwrites, recursively where nested values supply evidence. Only surviving entries establish row collisions, nested arrays, non-stringable objects, formatted numeric strings or nested list shapes. Earlier entries overwritten by a later occurrence of the same normalized key are not evidence; unknown keys or unsupported effective-array evaluation discard proof.
• 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.

Effective array-key behavior follows the PHP array contract.

Configure

In custos.json:

{
  "rules": {
    "ArrayColumnDuplicateIndexLoss": {
      "enabled": false
    }
  }
}

Suppress

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

// @custos-ignore ArrayColumnDuplicateIndexLoss