Enum PayloadHint 

#[non_exhaustive]
pub enum PayloadHint {
    Unknown,
    NoStructPayload,
    StructPayload,
}

Whether a structure has an @httpPayload member that supplies its own body framing, ex: a member carrying @httpPayload whose target is a structure or a union.

Why this is a hint and not a fact

The HTTP binding protocol needs this answer on every request, and deriving it means scanning the input schema’s members. Codegen already knows the answer, so it records it here and the runtime reads it instead of scanning.

Unknown is the default, and the runtime falls back to scanning when it sees it. That fallback is permanent, not transitional. Two callers rely on it:

• schemas constructed by hand or materialized at runtime, which have no codegen step to set the hint;
• generated crates produced before codegen began emitting the hint, which Cargo permits to link against a newer aws-smithy-schema within the same major version.

So this value must never become load-bearing for correctness. Anything that consumes it has to produce identical output for Unknown by deriving the answer itself.

Why the framing question rather than the payload’s shape

The variants deliberately answer “does a payload member frame the body?” rather than describing the payload’s type. @httpPayload may also target a blob, string, or document, and those are not grouped together by the runtime: blob and string payloads bypass the codec entirely (their bytes become the body verbatim), while a document payload is written through the codec. A variant named for one of those groupings would either be wrong or would have to change meaning if a consumer for the distinction appeared.

The enum is #[non_exhaustive], so a finer classification can be added later without a breaking change.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Unknown

Not recorded. Consumers must derive the answer themselves.

This is the default for every schema, including every hand-constructed one.

NoStructPayload

No member carries @httpPayload targeting a structure or union.

Body framing, if any, comes from the codec.

StructPayload

A member carries @httpPayload targeting a structure or union.

That member writes its own framing, so the codec must not add top-level framing around it.

Trait Implementations

impl Clone for PayloadHint

fn clone(&self) -> PayloadHint

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PayloadHint

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for PayloadHint

fn default() -> PayloadHint

Returns the “default value” for a type.

impl Hash for PayloadHint

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for PayloadHint

fn eq(&self, other: &PayloadHint) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for PayloadHint

impl Eq for PayloadHint

impl StructuralPartialEq for PayloadHint