Give CommonProblemDetailsExceptionTrait typed properties with safe defaults

[iloveyouinc]

Problem

CommonProblemDetailsExceptionTrait declares its private properties untyped with no defaults, while exposing typed getters (getTitle(): string, getType(): string, …). The trait's docblock says composing classes are required to set the properties — but when a composing class constructs an instance without setting all of them (a very easy thing to do in a consumer's own __construct, never routed through a ::create()-style factory), the contract violation surfaces as a confusing TypeError deep inside response generation:

$e = new class extends Exception implements ProblemDetailsExceptionInterface {
    use CommonProblemDetailsExceptionTrait;
};

$e->getTitle();
// TypeError: getTitle(): Return value must be of type string, null returned

In practice, ProblemDetailsResponseFactory::createResponseFromThrowable() calls these getters, so an exception that was meant to become a clean RFC 7807 4xx response instead becomes an unhandled 500 — the failure appears in the response pipeline, far from the actual mistake.

Fix

Type the properties and give them safe defaults:

private int $status = 500;
private string $detail = '';
private string $title = '';
private string $type = '';
/** @var array<string, mixed> */
private array $additional = [];

'' for title/type is exactly the sentinel ProblemDetailsResponseFactory already treats as "derive from status" (createResponse() fills the title from the status map and builds the httpstatus.es type URI), so a partially-initialized exception now renders as a well-formed problem-details response instead of fataling. The trait docblock is updated to document the defaults.

BC considerations

• The properties are private to the trait — only trait code and composing classes write them, so adding native types cannot break external writers.
• The only observable behavior change is on the previously-fatal path: code that would have thrown TypeError now returns the documented defaults.
• Composing classes that already initialize everything (including all ::create() users) are byte-for-byte unaffected.

Testing

Adds a regression test constructing a composing class that sets nothing and asserting all getters + toArray() return the defaults. composer test (82 tests / 451 assertions), composer cs-check, and composer static-analysis all pass locally on PHP 8.4.

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Found while maintaining a downstream fork where ~200 new SomeProblemException($detail) call sites each needed a hand-written constructor purely to avoid this TypeError; this change makes the trait fail-safe by construction.

🤖 Generated with Claude Code

[gsteel]

The properties are private to the trait — only trait code and composing classes write them, so adding native types cannot break external writers.

This is a library that ships a trait. All private properties of the trait are effectively part of the public API, so this is a BC break for anyone that uses it: https://3v4l.org/Zr2aL