PSA: LLCPP encoding/decoding APIs are unstable

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Yifei Teng

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Feb 8, 2022, 6:09:08 PM2/8/22

to fidl-dev, anno...@fuchsia.dev

~ If you don't use the low-level C++ bindings you may stop reading now ~

TLDR: The following classes will be moved to the `fidl::unstable` namespace:

- fidl::OwnedEncodedMessage<FidlType> - fidl::UnownedEncodedMessage<FidlType> - fidl::DecodedMessage<FidlType>

APIs in the `fidl::unstable` namespace are intentionally unstable: they may change or go away at any point. Please consider using other alternatives if possible when writing code in non-fuchsia.git repositories. Please refrain from using those in out-of-tree code (currently a small set of driver code).

Tracking bug: fxbug.dev/82681

Why are we doing this: These APIs lets users directly encode and decode FIDL domain objects without going through sending messages over protocol endpoints. They don't describe the wire format revision used in the encoding, hence are detrimental to wrei format evolution.

RFC-0120: Standalone use of the FIDL wire format ("FIDL at rest") is a project to replace these APIs with better ones that are aware of wire format revisions. To prepare for that, we are first moving the existing APIs to "unstable" status.

Please let us know on fidl...@fuchsia.dev if you have questions or suggestions. Thanks.