ra_salsa/
durability.rs

1/// Describes how likely a value is to change -- how "durable" it is.
2/// By default, inputs have `Durability::LOW` and interned values have
3/// `Durability::HIGH`. But inputs can be explicitly set with other
4/// durabilities.
5///
6/// We use durabilities to optimize the work of "revalidating" a query
7/// after some input has changed. Ordinarily, in a new revision,
8/// queries have to trace all their inputs back to the base inputs to
9/// determine if any of those inputs have changed. But if we know that
10/// the only changes were to inputs of low durability (the common
11/// case), and we know that the query only used inputs of medium
12/// durability or higher, then we can skip that enumeration.
13///
14/// Typically, one assigns low durabilities to inputs that the user is
15/// frequently editing. Medium or high durabilities are used for
16/// configuration, the source from library crates, or other things
17/// that are unlikely to be edited.
18#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
19pub struct Durability(u8);
20
21impl Durability {
22    /// Low durability: things that change frequently.
23    ///
24    /// Example: part of the crate being edited
25    pub const LOW: Durability = Durability(0);
26
27    /// Medium durability: things that change sometimes, but rarely.
28    ///
29    /// Example: a Cargo.toml file
30    pub const MEDIUM: Durability = Durability(1);
31
32    /// High durability: things that are not expected to change under
33    /// common usage.
34    ///
35    /// Example: the standard library or something from crates.io
36    pub const HIGH: Durability = Durability(2);
37
38    /// The maximum possible durability; equivalent to HIGH but
39    /// "conceptually" distinct (i.e., if we add more durability
40    /// levels, this could change).
41    pub(crate) const MAX: Durability = Self::HIGH;
42
43    /// Number of durability levels.
44    pub(crate) const LEN: usize = Self::MAX.index() + 1;
45
46    pub(crate) const fn index(self) -> usize {
47        self.0 as usize
48    }
49}
ra_salsa/durability.rs

ra_salsa/
durability.rs
