[Php80] Skip mixed and untyped calls in TernaryToNullsafeCoalesceRector

[roxblnfk]

🔍 What was changed

TernaryToNullsafeCoalesceRector no longer rewrites a ternary to ?->… ?? $fallback when the call or property fetch returns mixed or has no declared type. Only calls whose type excludes null for sure are rewritten now.

Why?

The guard shouldSkipCoalesceFallback() relied on TypeCombinator::containsNull(), which returns false for MixedType — it only detects an explicit NullType or a union containing it. A null returned by such a call then fell through to the fallback, changing behavior:

// before: core returning null yields null
return $this->core === null
    ? $this->handler->handle($context)
    : $this->core->callAction(...); // callAction(): mixed

// after the rule: core returning null calls $this->handler, which is null here → Error
return $this->core?->callAction(...) ?? $this->handler->handle($context);

This broke InterceptorPipeline::handle() in spiral/framework (spiral/framework#1307).

Checklist

• How was this tested:
  • Unit tests added
  • rules-tests/Php80 suite and PHPStan on the rule run locally

[samsonasik]

Looks good

[TomasVotruba]

LGTM