MonthAdditionDateOverflow

warning native off by default

Group: Probable bugs

Detect modify with literal +1 month or -1 month on a resolved literal date when the target month cannot contain the original day number.

Example

<?php
$next=(new DateTimeImmutable('2025-01-31'))->modify('+1 month');

Reported:

• line 2: Choose an explicit month-end overflow policy.

Detection

• Report modify with literal +1 month or -1 month on a resolved literal date when the target month cannot contain the original day number.
• Resolve builtin calls and named arguments before checking the contract. Project-local callees are considered only when their bodies or immutable summaries establish the required facts. The default is disabled; enable only when the stated intent matches the application.
• For flow-dependent conditions, require a reachable source-to-use path with no intervening invalidation. Unknown calls, ambiguous aliases, recursion or analysis-budget exhaustion cannot establish definite facts.

Exceptions (no report)

• Dates valid in both months, explicit overflow intent, guarded/clamped arithmetic and unknown dates are excluded.
• Unresolved targets, incomplete required facts, suppressed findings and PHP versions lacking the referenced API or language feature produce no report. User declarations shadowing builtin names are not builtin contracts.

Fix

No automatic fix: clamping, rolling and rejecting are distinct month-end policies.

PHP versions

Apply only on PHP versions supporting the referenced APIs and syntax (within PHP 5.3–8.5). Builtin behavior and argument contracts follow the configured PHP version. Extension-specific calls require resolved extension API symbols; do not treat same-named application functions as extension calls.

Options

None. Enable or disable this rule through normal rule configuration.

Configure

In custos.json:

{
  "rules": {
    "MonthAdditionDateOverflow": {
      "enabled": true
    }
  }
}

Suppress

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

// @custos-ignore MonthAdditionDateOverflow