diff --git a/src/salsa.md b/src/salsa.md index a49c324d..8d21b454 100644 --- a/src/salsa.md +++ b/src/salsa.md @@ -4,17 +4,17 @@ This chapter is based on the explanation given by Niko Matsakis in this [video](https://www.youtube.com/watch?v=_muY4HjSqVw) about -[Salsa](https://github.com/salsa-rs/salsa). To find out more you may -want to watch [Salsa In More +[`Salsa`](https://github.com/salsa-rs/salsa). To find out more you may +want to watch [`Salsa` In More Depth](https://www.youtube.com/watch?v=i_IhACacPRY), also by Niko Matsakis. -> As of November 2022, although Salsa is inspired by -> (among other things) rustc's query system, it is not used directly in rustc. -> It _is_ used in [chalk], an implementation of Rust's trait system, and extensively in -> [`rust-analyzer`], the official implementation of the language server protocol for Rust, but -> there are no medium or long-term concrete plans to integrate it into the -> compiler. +> As of November 2022, although `Salsa` is inspired by (among +> other things) `rustc`'s query system, it is not used directly in `rustc`. It +> _is_ used in [chalk], an implementation of Rust's trait system, and +> extensively in [`rust-analyzer`], the official implementation of the language +> server protocol for Rust, but there are no medium or long-term concrete +> plans to integrate it into the compiler. [`rust-analyzer`]: https://rust-analyzer.github.io/ @@ -22,19 +22,19 @@ Matsakis. ## What is Salsa? -Salsa is a library for incremental recomputation. This means it allows reusing +`Salsa` is a library for incremental recomputation. This means it allows reusing computations that were already done in the past to increase the efficiency of future computations. -The objectives of Salsa are: +The objectives of `Salsa` are: * Provide that functionality in an automatic way, so reusing old computations - is done automatically by the library + is done automatically by the library. * Doing so in a "sound", or "correct", way, therefore leading to the same - results as if it had been done from scratch + results as if it had been done from scratch. -Salsa's actual model is much richer, allowing many kinds of inputs and many +`Salsa`'s actual model is much richer, allowing many kinds of inputs and many different outputs. -For example, integrating Salsa with an IDE could mean that the inputs could be +For example, integrating `Salsa` with an IDE could mean that the inputs could be the manifest (`Cargo.toml`), entire source files (`foo.rs`), snippets and so on; the outputs of such an integration could range from a binary executable, to lints, types (for example, if a user selects a certain variable and wishes to @@ -42,10 +42,10 @@ see its type), completions, etc. ## How does it work? -The first thing that Salsa has to do is identify the "base inputs" that +The first thing that `Salsa` has to do is identify the "base inputs" that are not something computed but given as input. -Then Salsa has to also identify intermediate, "derived" values, which are +Then `Salsa` has to also identify intermediate, "derived" values, which are something that the library produces, but, for each derived value there's a "pure" function that computes the derived value. @@ -53,16 +53,16 @@ For example, there might be a function `ast(x: Path) -> AST`. The produced `AST` isn't a final value, it's an intermediate value that the library would use for the computation. -This means that when you try to compute with the library, Salsa is going to +This means that when you try to compute with the library, `Salsa` is going to compute various derived values, and eventually read the input and produce the result for the asked computation. -In the course of computing, Salsa tracks which inputs were accessed and which +In the course of computing, `Salsa` tracks which inputs were accessed and which values are derived. This information is used to determine what's going to happen when the inputs change: are the derived values still valid? This doesn't necessarily mean that each computation downstream from the input -is going to be checked, which could be costly. Salsa only needs to check each +is going to be checked, which could be costly. `Salsa` only needs to check each downstream computation until it finds one that isn't changed. At that point, it won't check other derived computations since they wouldn't need to change. @@ -78,7 +78,7 @@ J <- B <--+ When an input `I` changes, the derived value `A` could change. The derived value `B`, which does not depend on `I`, `A`, or any value derived from `A` or -`I`, is not subject to change. Therefore, Salsa can reuse the computation done +`I`, is not subject to change. Therefore, `Salsa` can reuse the computation done for `B` in the past, without having to compute it again. The computation could also terminate early. Keeping the same graph as before, @@ -88,29 +88,29 @@ computation. This leads to an "early termination", because there's no need to check if `C` needs to change, since both `C` direct inputs, `A` and `B`, haven't changed. -## Key Salsa concepts +## Key `Salsa` concepts ### Query -A query is some value that Salsa can access in the course of computation. Each +A query is some value that `Salsa` can access in the course of computation. Each query can have a number of keys (from 0 to many), and all queries have a -result, akin to functions. 0-key queries are called "input" queries. +result, akin to functions. `0-key` queries are called "input" queries. ### Database The database is basically the context for the entire computation, it's meant to -store Salsa's internal state, all intermediate values for each query, and -anything else that the computation might need. The database must know all the -queries that the library is going to do before it can be built, but they don't -need to be specified in the same place. +store `Salsa`'s internal state, all intermediate values for each query, and +anything else that the computation might need. The database must know all the +queries the library is going to do before it can be built, but they don't need +to be specified in the same place. After the database is formed, it can be accessed with queries that are very -similar to functions. Since each query's result is stored in the database, -when a query is invoked N times, it will return N **cloned** results, without -having to recompute the query (unless the input has changed in such a way that -it warrants recomputation). +similar to functions. Since each query's result is stored in the database, when +a query is invoked `N`-times, it will return `N`-**cloned** results, without having +to recompute the query (unless the input has changed in such a way that it +warrants recomputation). -For each input query (0-key), a "set" method is generated, allowing the user to +For each input query (`0-key`), a "set" method is generated, allowing the user to change the output of such query, and trigger previous memoized values to be potentially invalidated. @@ -118,7 +118,7 @@ potentially invalidated. A query group is a set of queries which have been defined together as a unit. The database is formed by combining query groups. Query groups are akin to -"Salsa modules". +"`Salsa` modules". A set of queries in a query group are just a set of methods in a trait. @@ -132,7 +132,7 @@ Example input query group: ```rust,ignore /// This attribute will process this tree, produce this tree as output, and produce -/// a bunch of intermediate stuff that Salsa also uses. One of these things is a +/// a bunch of intermediate stuff that Salsa also uses. One of these things is a /// "StorageStruct", whose name we have specified in the attribute. /// /// This query group is a bunch of **input** queries, that do not rely on any @@ -154,9 +154,9 @@ this one depends on by specifying them as supertraits, as seen in the following example: ```rust,ignore -/// This query group is going to contain queries that depend on derived values. A -/// query group can access another query group's queries by specifying the -/// dependency as a super trait. Query groups can be stacked as much as needed using +/// This query group is going to contain queries that depend on derived values. +/// A query group can access another query group's queries by specifying the +/// dependency as a supertrait. Query groups can be stacked as much as needed using /// that pattern. #[salsa::query_group(ParserStorage)] pub trait Parser: Inputs { @@ -172,10 +172,11 @@ Trait` (or `dyn Trait`), where `Trait` is the query group that the definition belongs to, in addition to the other keys. ```rust,ignore -///This is going to be the definition of the `ast` query in the `Parser` trait. -///So, when the query `ast` is invoked, and it needs to be recomputed, Salsa is going to call this function -///and it's going to give it the database as `impl Parser`. -///The function doesn't need to be aware of all the queries of all the query groups +/// This is going to be the definition of the `ast` query in the `Parser` trait. +/// So, when the query `ast` is invoked, and it needs to be recomputed, Salsa is +/// going to call this function and it's going to give it the database as `impl +/// Parser`. The function doesn't need to be aware of all the queries of all the +/// query groups fn ast(db: &impl Parser, name: String) -> String { //! Note, `impl Parser` is used here but `dyn Parser` works just as well /* code */