Enum DegradeRule 

pub enum DegradeRule {
    StructuredContentToText,
    DropAnnotations,
    AudioToTextPlaceholder,
    DropAudio,
    DropImage,
    DropResourceLink,
    DropResource,
}

One thing lowering may do to make a value expressible.

Variants

StructuredContentToText

Serialise structuredContent into a text content block.

Added 2025-06-18; the specification names this as the recommended fallback. Lossless: the bytes are unchanged, only the carrier differs.

DropAnnotations

Drop annotations a revision does not define.

Loss::Flagged. Annotations arrived in 2025-03-26 and a 2024-11-05 peer simply ignores them, so nothing that peer could have acted on is lost — but a bridge that drops them without saying so is lying about what happened.

AudioToTextPlaceholder

Replace an audio block with a text placeholder naming it.

Loss::Destructive, and there is no lossless alternative: there is no textual stand-in for audio. For this reason it is the one rule the specification does not sanction, and a caller must name it.

DropAudio

Drop an audio block.

DropImage

Drop an image block.

DropResourceLink

Drop a resource link, 2025-06-18 and later.

DropResource

Drop an embedded resource.

Implementations

impl DegradeRule

pub const ALL: &'static [Self]

Every rule a DegradePolicy can select to satisfy a missing feature, in a stable order so a policy set or a report reads the same way twice.

Every rule here names a feature, which is the invariant that keeps the list honest: a rule in this list is reachable by rule_for, and a rule that is not in it is not reachable by a policy at all.

The three that are not listed — AudioToTextPlaceholder, DropImage and DropResource — are opt-in reductions rather than fallbacks. The placeholder because the specification does not sanction it and dropping the block is the only policy-selectable response to audio; the other two because images and embedded resources are expressible at every revision, so no revision’s absence ever requires dropping them. Listing any of them would let rule_for hand back something a caller never asked for, or that could never apply.

pub const fn feature(self) -> Option<Feature>

The feature whose absence this rule exists to work around.

None for a rule that is not a fallback — a reduction a caller opts into for its own reasons, not something a revision forces. Images and embedded resources have been expressible since 2024-11-05 and annotations are simply ignored by older peers, so there is no revision whose absence ever makes dropping them necessary. Reporting a feature for them would be a lie about why the rule exists, and would make rule_for offer them as answers to a question they cannot answer.

pub const fn loss(self) -> Loss

How much this rule gives up.

Only DropAnnotations is Loss::Flagged. Every rule that removes a content block is Loss::Destructive, because a block the tool produced is the tool’s answer: dropping it does not degrade the message, it makes it say something the tool did not. Calling that “flagged” would let a bridge promise “lossless or flagged” and quietly remove content.

pub fn is_fallback_for(self, feature: Feature) -> bool

Whether this rule is the one that makes a value needing feature expressible again.

Not const: Feature’s PartialEq is not const-callable, the same trade T05 made on defined_in.

Trait Implementations

impl Clone for DegradeRule

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for DegradeRule

impl Debug for DegradeRule

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

Formats the value using the given formatter.

impl Eq for DegradeRule

impl Hash for DegradeRule

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 Ord for DegradeRule

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for DegradeRule

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

Equality operator ==.

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

Inequality operator !=.

impl PartialOrd for DegradeRule

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for DegradeRule