D395 - An undocumented out-parameter is refused, or measured, never invented

Status: decided Date: 2026-08-30

A call filling a structure whose field layout no lawful source describes answers a negative status by default; under a diagnostic setting it instead fills the structure with markers that name their own offset, so a guest's own reads reveal which fields it actually wants.

Why: Inventing a plausible layout produces a run that looks like it worked while feeding a guest fields that mean nothing; refusing outright is honest but stops short of measuring, when the guest itself is the source that can settle it. A negative status is also the right shape for a failure - a small positive placeholder reads to a status-checking caller as success.

Rejected:

• Filling the structure with an invented plausible layout: not sourced from anything, and a guest that reads it acts on a fabrication.
• Refusing without ever measuring: leaves the real layout permanently unknown when the guest could reveal it a field at a time.