Enum QueryResult 

pub enum QueryResult<T> {
    Ok(T),
    Err(String),
}

Result wrapper for Salsa queries that can fail.

Why not std::result::Result?

Salsa’s memoization requires return types to implement Clone, PartialEq, Eq, and Hash. While std::result::Result<T, E> implements these traits when T and E do, using a dedicated type provides:

1. Simpler error type: Always String, avoiding generic error handling
2. Explicit intent: Clearly marks Salsa-compatible error boundaries
3. Consistent API: All Venus queries use the same error pattern

Usage Pattern

Most queries come in pairs: a *_result variant that returns errors, and a convenience variant that returns a default on failure:

// Option 1: Handle errors explicitly
match db.get_execution_order_result(source) {
    QueryResult::Ok(order) => process(order),
    QueryResult::Err(e) => log_error(e),
}

// Option 2: Use default on error (empty vec)
let order = db.get_execution_order(source); // Returns empty vec on error

Use the *_result variant when you need to:

• Display error messages to users
• Distinguish “no cells found” from “parse error”
• Propagate errors to callers

Variants

Ok(T)

Query succeeded with a result

Err(String)

Query failed with an error message

Implementations

impl<T> QueryResult<T>

pub fn is_ok(&self) -> bool

Returns true if the query succeeded.

pub fn is_err(&self) -> bool

Returns true if the query failed.

pub fn ok(&self) -> Option<&T>

Get the result if successful.

pub fn err(&self) -> Option<&str>

Get the error message if failed.

pub fn unwrap(self) -> T

Unwrap the result, panicking if it’s an error.

Panics

Panics with the error message if the query failed. This is intentional for cases where failure indicates a programming error (e.g., in tests). For production code, prefer [ok()], [unwrap_or()], or pattern matching.

pub fn unwrap_or(self, default: T) -> T

Unwrap the result or return a default value.

This is the recommended way to handle errors when you have a sensible default (e.g., empty vector for missing data).

Trait Implementations

impl<T: Clone> Clone for QueryResult<T>

fn clone(&self) -> QueryResult<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for QueryResult<T>

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

Formats the value using the given formatter.

impl<T: Hash> Hash for QueryResult<T>

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<T: PartialEq> PartialEq for QueryResult<T>

fn eq(&self, other: &QueryResult<T>) -> 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<T: Eq> Eq for QueryResult<T>

impl<T> StructuralPartialEq for QueryResult<T>