Display documentation for sway keywords (FuelLabs#3792)

This PR provides documentation when hovering over keywords in sway. I
copied over the documentation for keywords that are shared with rust and
tweaked them so they made sense to sway [from
here](https://github.com/rust-lang/rust/blob/master/library/std/src/keyword_docs.rs
).

It would be great to get some compiler engineers to look over the
documentation to make sure nothing is being incorrectly defined.

There are still a number of keywords that need documentation written up
for them but I've opened up FuelLabs#3939 so these can be added by someone on
the compiler team at a later date.

will close FuelLabs#3515

---------

sway-lsp/Cargo.toml

@@ -16,6 +16,8 @@ forc-tracing = { version = "0.34.0", path = "../forc-tracing" }
 notify = "5.0.0"
 notify-debouncer-mini = { version = "0.2.0" }
 parking_lot = "0.12.1"
+proc-macro2 = "1.0.5"
+quote = "1.0.9"
 ropey = "1.2"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0.60"
@@ -26,6 +28,7 @@ sway-parse = { version = "0.34.0", path = "../sway-parse" }
 sway-types = { version = "0.34.0", path = "../sway-types" }
 sway-utils = { version = "0.34.0", path = "../sway-utils" }
 swayfmt = { version = "0.34.0", path = "../swayfmt" }
+syn = { version = "1.0.73", features = ["full"] }
 tempfile = "3"
 thiserror = "1.0.30"
 tokio = { version = "1.3", features = ["io-std", "io-util", "macros", "net", "rt-multi-thread", "sync", "time"] }

sway-lsp/src/capabilities/hover.rs

@@ -1,9 +1,11 @@
 use crate::{
     core::{
         session::Session,
-        token::{get_range_from_span, to_ident_key, Token, TypedAstToken},
+        token::{get_range_from_span, to_ident_key, SymbolKind, Token, TypedAstToken},
+    },
+    utils::{
+        attributes::doc_comment_attributes, keyword_docs::KeywordDocs, markdown, markup::Markup,
     },
-    utils::{attributes::doc_comment_attributes, markdown, markup::Markup},
 };
 use std::sync::Arc;
 use sway_core::{
@@ -14,9 +16,29 @@ use sway_types::{Ident, Span, Spanned};
 use tower_lsp::lsp_types::{self, Position, Url};
 
 /// Extracts the hover information for a token at the current position.
-pub fn hover_data(session: Arc<Session>, url: Url, position: Position) -> Option<lsp_types::Hover> {
+pub fn hover_data(
+    session: Arc<Session>,
+    keyword_docs: &KeywordDocs,
+    url: Url,
+    position: Position,
+) -> Option<lsp_types::Hover> {
     let (ident, token) = session.token_map().token_at_position(&url, position)?;
     let range = get_range_from_span(&ident.span());
+
+    // check if our token is a keyword
+    if token.kind == SymbolKind::Keyword {
+        let name = ident.as_str();
+        let documentation = keyword_docs.get(name).unwrap();
+        let prefix = format!("\n```sway\n{name}\n```\n\n---\n\n");
+        let formatted_doc = format!("{prefix}{documentation}");
+        let content = Markup::new().text(&formatted_doc);
+        let contents = lsp_types::HoverContents::Markup(markup_content(content));
+        return Some(lsp_types::Hover {
+            contents,
+            range: Some(range),
+        });
+    }
+
     let (decl_ident, decl_token) = match token.declared_token_ident(&session.type_engine.read()) {
         Some(decl_ident) => {
             let decl_token = session

sway-lsp/src/server.rs

@@ -4,7 +4,7 @@ use crate::{
     config::{Config, Warnings},
     core::{session::Session, sync},
     error::{DirectoryError, LanguageServerError},
-    utils::debug,
+    utils::{debug, keyword_docs::KeywordDocs},
 };
 use dashmap::DashMap;
 use forc_pkg::manifest::PackageManifestFile;
@@ -27,17 +27,20 @@ use tracing::metadata::LevelFilter;
 pub struct Backend {
     pub client: Client,
     pub config: RwLock<Config>,
+    pub keyword_docs: KeywordDocs,
     sessions: DashMap<PathBuf, Arc<Session>>,
 }
 
 impl Backend {
     pub fn new(client: Client) -> Self {
         let sessions = DashMap::new();
         let config = RwLock::new(Default::default());
+        let keyword_docs = KeywordDocs::new();
 
         Backend {
             client,
             config,
+            keyword_docs,
             sessions,
         }
     }
@@ -302,7 +305,12 @@ impl LanguageServer for Backend {
         match self.get_uri_and_session(&params.text_document_position_params.text_document.uri) {
             Ok((uri, session)) => {
                 let position = params.text_document_position_params.position;
-                Ok(capabilities::hover::hover_data(session, uri, position))
+                Ok(capabilities::hover::hover_data(
+                    session,
+                    &self.keyword_docs,
+                    uri,
+                    position,
+                ))
             }
             Err(err) => {
                 tracing::error!("{}", err.to_string());