## About the guide
-This guide describes the current start of the rust-analyzer as of 2019-01-20
+This guide describes the current state of `rust-analyzer` as of 2019-01-20
(git tag [guide-2019-01]). Its purpose is to document various problems and
architectural solutions related to the problem of building IDE-first compiler
for Rust.
## The big picture
-On the highest possible level, rust analyzer is a stateful component. Client may
+On the highest possible level, rust analyzer is a stateful component. A client may
apply changes to the analyzer (new contents of `foo.rs` file is "fn main() {}")
and it may ask semantic questions about the current state (what is the
definition of the identifier with offset 92 in file `bar.rs`?). Two important
properties hold:
-* Analyzer does not do any IO. It starts in an empty state and all input data is
+* Analyzer does not do any I/O. It starts in an empty state and all input data is
provided via `apply_change` API.
* Only queries about the current state are supported. One can, of course,
- simulate undo and redo by keeping log of changes and inverse-changes.
+ simulate undo and redo by keeping a log of changes and inverse changes respectively.
## IDE API
-To see this big picture, let's take a look at the [`AnalysisHost`] and
+To see the bigger picture of how the IDE features works, let's take a look at the [`AnalysisHost`] and
[`Analysis`] pair of types. `AnalysisHost` has three methods:
-* `default` for creating an empty analysis
+* `default()` for creating an empty analysis instance
* `apply_change(&mut self)` to make changes (this is how you get from an empty
state to something interesting)
* `analysis(&self)` to get an instance of `Analysis`
[`AnalysisHost`]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_ide_api/src/lib.rs#L265-L284
[`Analysis`]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_ide_api/src/lib.rs#L291-L478
-The reason for `Analysis` and `AnalysisHost` separation is that we want apply
-changes "uniquely", but we might want to fork an `Analysis` and send it to
+The reason for this separation of `Analysis` and `AnalysisHost` is that we want to apply
+changes "uniquely", but we might also want to fork an `Analysis` and send it to
another thread for background processing. That is, there is only a single
`AnalysisHost`, but there may be several (equivalent) `Analysis`.
Note that all of the `Analysis` API return `Cancelable<T>`. This is required to
-be responsive in IDE setting. Sometimes a long-running query is being computed
+be responsive in an IDE setting. Sometimes a long-running query is being computed
and the user types something in the editor and asks for completion. In this
case, we cancel the long-running computation (so it returns `Err(Canceled)`),
apply the change and execute request for completion. We never use stale data to
answer requests. Under the cover, `AnalysisHost` "remembers" all outstanding
-`Analysis` instances. `AnalysisHost::apply_change` method cancels all
-`Analysis`es, blocks until of them are `Dropped` and then applies change
-in-place. This is the familiar to rustaceans read-write lock interior
+`Analysis` instances. The `AnalysisHost::apply_change` method cancels all
+`Analysis`es, blocks until all of them are `Dropped` and then applies changes
+in-place. This may be familiar to Rustaceans who use read-write locks for interior
mutability.
-Next, lets talk about what are inputs to the Analysis, precisely.
+Next, let's talk about what the inputs to the `Analysis` are, precisely.
## Inputs
-Rust Analyzer never does any IO itself, all inputs get passed explicitly via
-`AnalysisHost::apply_change` method, which accepts a single argument:
+Rust Analyzer never does any I/O itself, all inputs get passed explicitly via
+the `AnalysisHost::apply_change` method, which accepts a single argument, a
`AnalysisChange`. [`AnalysisChange`] is a builder for a single change
"transaction", so it suffices to study its methods to understand all of the
input data.
The `(add|change|remove)_file` methods control the set of the input files, where
each file has an integer id (`FileId`, picked by the client), text (`String`)
-and a filesystem path. Paths are tricky, they'll be explained in source roots
-section, together with `add_root` method. `add_library` method allows to add a
+and a filesystem path. Paths are tricky; they'll be explained below, in source roots
+section, together with the `add_root` method. The `add_library` method allows us to add a
group of files which are assumed to rarely change. It's mostly an optimization
-and does not change fundamental picture.
+and does not change the fundamental picture.
-`set_crate_graph` method allows to control how the input files are partitioned
+The `set_crate_graph` method allows us to control how the input files are partitioned
into compilation unites -- crates. It also controls (in theory, not implemented
yet) `cfg` flags. `CrateGraph` is a directed acyclic graph of crates. Each crate
has a root `FileId`, a set of active `cfg` flags and a set of dependencies. Each
* **Functions**: pure functions (no side effects) that transform your inputs
into other values. The results of queries is memoized to avoid recomputing
- them a lot. When you make changes to the inputs, we'll figure out (fairlywe
- intelligently) when we can re-use these memoized values and when we have we
+ them a lot. When you make changes to the inputs, we'll figure out (fairly
+ intelligently) when we can re-use these memoized values and when we have to
recompute them.
For further discussion, its important to understand one bit of "fairly
-intelligently". Suppose we have to functions, `f1` and `f2`, and one input,we
+intelligently". Suppose we have two functions, `f1` and `f2`, and one input, `z`.
We call `f1(X)` which in turn calls `f2(Y)` which inspects `i(Z)`. `i(Z)`
-returns some value `V1`, `f2` uses that and returns `R1`, `f1` uses that anwe
-returns `O`. Now, let's change `i` at `Z` to `V2` from `V1` and try to compwe
-`f1(X)` again. Because `f1(X)` (transitively) depends on `i(Z)`, we can't jwe
-reuse its value as is. However, if `f2(Y)` is *still* equal to `R1` (despitwe
-`i`'s change), we, in fact, *can* reuse `O` as result of `f1(X)`. And that'we
-salsa works: it recomputes results in *reverse* order, starting from inputswe
-progressing towards outputs, stopping as soon as it sees an intermediate vawe
+returns some value `V1`, `f2` uses that and returns `R1`, `f1` uses that and
+returns `O`. Now, let's change `i` at `Z` to `V2` from `V1` and try to compute
+`f1(X)` again. Because `f1(X)` (transitively) depends on `i(Z)`, we can't just
+reuse its value as is. However, if `f2(Y)` is *still* equal to `R1` (despite
+`i`'s change), we, in fact, *can* reuse `O` as result of `f1(X)`. And that's how
+salsa works: it recomputes results in *reverse* order, starting from inputs and
+progressing towards outputs, stopping as soon as it sees an intermediate value
that hasn't changed.
## Salsa Input Queries
`Option`s. The tree for `fn foo` will contain a function declaration with
`None` for parameter list and body.
-* Syntax trees do not know the file they are build from, they only know about
+* Syntax trees do not know the file they are built from, they only know about
the text.
The implementation is based on the generic [rowan] crate on top of which a
First, rust analyzer builds a module tree for all crates in a source root
simultaneously. The main reason for this is historical (`module_tree` predates
-`CrateGraph`), but this approach also allows to account for files which are not
+`CrateGraph`), but this approach also enables accounting for files which are not
part of any crate. That is, if you create a file but do not include it as a
submodule anywhere, you still get semantic completion, and you get a warning
-about free-floating module (the actual warning is not implemented yet).
+about a free-floating module (the actual warning is not implemented yet).
The second difference is that `module_tree_query` does not *directly* depend on
the "parse" query (which is confusingly called `source_file`). Why would calling
it includes whitespace), and that means recomputing the whole module tree.
We deal with this problem by introducing an intermediate [`submodules_query`].
-This query processes the syntax tree an extract a set of declared submodule
+This query processes the syntax tree and extracts a set of declared submodule
names. Now, changing the whitespace results in `submodules_query` being
re-executed for a *single* module, but because the result of this query stays
the same, we don't have to re-execute [`module_tree_query`]. In fact, we only
need to re-execute it when we add/remove new files or when we change mod
declarations.
-[`submodules_query`]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/module_tree.rs#L41)
+[`submodules_query`]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/module_tree.rs#L41
We store the resulting modules in a `Vec`-based indexed arena. The indices in
the arena becomes module ids. And this brings us to the next topic:
we've reached a fixed point.
[lower]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/nameres/lower.rs#L113-L117
-[loop]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/nameres/lower.rs#L113-L117
+[loop]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/nameres.rs#L186-L196
And, given all our preparation with ids and position-independent representation,
it is satisfying to [test] that typing inside function body does not invalidate
[lower ast]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/expr.rs
[positional id]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/expr.rs#L13-L15
[a source map]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/expr.rs#L41-L44
-[type-inference]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/ty.rs#L1208-L1223
+[type inference]: https://github.com/rust-analyzer/rust-analyzer/blob/guide-2019-01/crates/ra_hir/src/ty.rs#L1208-L1223
## Tying it all together: completion
projects / rust.git / commitdiff