Struct ExpectationFailure 

pub struct ExpectationFailure {

    pub ok: False,
    pub code: FailureCode,
    pub message: String,
    pub selector: Option<Selector>,
    pub suggestions: Vec<String>,
    pub visible_elements: Vec<ElementSummary>,
    pub hint: Option<String>,
    pub smix_version: String,
    pub screenshot: Option<String>,
    pub device_log: Vec<String>,
    pub visible_total: Option<usize>,
    pub windows: Vec<WindowInfo>,
    pub unreadable_windows: Option<u32>,
}

Structured failure thrown by SDK matchers and driver calls. Shape is AI-feed-back-ready.

selector is the typed Selector rather than the wire serde_json::Value — callers raising failures from the driver / SDK side already have the typed selector, and to_prompt invokes describe_selector for stable rendering.

Serializes as { ok: false, code, message, selector, suggestions, visibleElements, hint, screenshot, deviceLog }; the ok = false discriminant identifies the failure branch of a Result wire.

Fields

ok: False

Always false for failures. Round-trip discriminator for Result<T, ExpectationFailure> wire.

code: FailureCode

Failure code discriminator.

message: String

Human-readable summary (and AI-readable when fed into to_prompt).

selector: Option<Selector>

Originating selector, when one is available.

suggestions: Vec<String>

Ranked near-miss suggestions (edit-distance to label / id / etc.).

visible_elements: Vec<ElementSummary>

Snapshot of visible+enabled elements at failure time.

hint: Option<String>

Optional one-line hint (e.g. “try app.wait_for(...) first”).

smix_version: String

The smix that produced this failure.

Not decoration. A consumer wrote up two defects against smix behaviour that had been fixed hours earlier, quoting an error message the current build no longer emits — they had no way to tell whether the smix in front of them contained the fix for the thing they had just hit. A failure that names its version makes that answerable from the failure itself.

Set by ExpectationFailure::new from the crate version, so no call site can forget it.

screenshot: Option<String>

base64-encoded PNG; omitted from default rendering to keep logs lean.

device_log: Vec<String>

Last-N-lines of captured device log, folded into AI-readable output for failure-window system context.

visible_total: Option<usize>

How many elements visible_elements was cut from.

A list of ten read as the whole screen: a consumer built a detector on it that called every Android failure blind, because the ten were always the status bar. The total says it is a sample.

windows: Vec<WindowInfo>

The windows the screen held when this failed, focused app first.

unreadable_windows: Option<u32>

Windows the reader could not read. “The app is not in the tree” and “the app’s window could not be read” are different failures.

Implementations

impl ExpectationFailure

pub fn new(init: FailureInit) -> Self

Construct from an init struct. code defaults to DriverError if init.code was None (defensive; SDK callers should always set it).

pub fn to_prompt(&self) -> String

AI-facing rendering. Designed so the output can be pasted back as a user message into a coding agent.

Trait Implementations

impl Clone for ExpectationFailure

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ExpectationFailure

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for ExpectationFailure

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for ExpectationFailure

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

Formats the value using the given formatter.

impl Error for ExpectationFailure

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

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

Provides type-based access to context intended for error reports.

impl Serialize for ExpectationFailure

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.