This commit add Cargo-style project discovery for Buck and Bazel users.

This feature requires the user to add a command that generates a
`rust-project.json` from a set of files. Project discovery can be invoked
in two ways:

1. At extension activation time, which includes the generated
   `rust-project.json` as part of the linkedProjects argument in
    InitializeParams
2. Through a new command titled "Add current file to workspace", which
   makes use of a new, rust-analyzer specific LSP request that adds
   the workspace without erasing any existing workspaces.

I think that the command-running functionality _could_ merit being
placed into its own extension (and expose it via extension contribution
points), if only provide build-system idiomatic progress reporting and
status handling, but I haven't (yet) made an extension that does this.

crates/rust-analyzer/src/config.rs

@@ -272,7 +272,6 @@ config_data! {
         /// The warnings will be indicated by a blue squiggly underline in code
         /// and a blue icon in the `Problems Panel`.
         diagnostics_warningsAsInfo: Vec<String> = "[]",
-
         /// These directories will be ignored by rust-analyzer. They are
         /// relative to the workspace root, and globs are not supported. You may
         /// also need to add the folders to Code's `files.watcherExclude`.
@@ -895,6 +894,15 @@ impl Config {
         }
     }
 
+    pub fn add_linked_projects(&mut self, linked_projects: Vec<ProjectJsonData>) {
+        let mut linked_projects = linked_projects
+            .into_iter()
+            .map(ManifestOrProjectJson::ProjectJson)
+            .collect::<Vec<ManifestOrProjectJson>>();
+
+        self.data.linkedProjects.append(&mut linked_projects);
+    }
+
     pub fn did_save_text_document_dynamic_registration(&self) -> bool {
         let caps = try_or_def!(self.caps.text_document.as_ref()?.synchronization.clone()?);
         caps.did_save == Some(true) && caps.dynamic_registration == Some(true)

crates/rust-analyzer/src/handlers.rs

@@ -5,6 +5,7 @@
 use std::{
     io::Write as _,
     process::{self, Stdio},
+    sync::Arc,
 };
 
 use anyhow::Context;
@@ -46,6 +47,22 @@ use crate::{
 pub(crate) fn handle_workspace_reload(state: &mut GlobalState, _: ()) -> Result<()> {
     state.proc_macro_clients.clear();
     state.proc_macro_changed = false;
+
+    state.fetch_workspaces_queue.request_op("reload workspace request".to_string());
+    state.fetch_build_data_queue.request_op("reload workspace request".to_string());
+    Ok(())
+}
+
+pub(crate) fn handle_add_project(
+    state: &mut GlobalState,
+    params: lsp_ext::AddProjectParams,
+) -> Result<()> {
+    state.proc_macro_clients.clear();
+    state.proc_macro_changed = false;
+
+    let config = Arc::make_mut(&mut state.config);
+    config.add_linked_projects(params.project);
+
     state.fetch_workspaces_queue.request_op("reload workspace request".to_string());
     state.fetch_build_data_queue.request_op("reload workspace request".to_string());
     Ok(())

crates/rust-analyzer/src/lsp_ext.rs

@@ -9,6 +9,7 @@ use lsp_types::{
     notification::Notification, CodeActionKind, DocumentOnTypeFormattingParams,
     PartialResultParams, Position, Range, TextDocumentIdentifier, WorkDoneProgressParams,
 };
+use project_model::ProjectJsonData;
 use serde::{Deserialize, Serialize};
 
 use crate::line_index::PositionEncoding;
@@ -51,6 +52,20 @@ impl Request for ReloadWorkspace {
     const METHOD: &'static str = "rust-analyzer/reloadWorkspace";
 }
 
+pub enum AddProject {}
+
+impl Request for AddProject {
+    type Params = AddProjectParams;
+    type Result = ();
+    const METHOD: &'static str = "rust-analyzer/addProject";
+}
+
+#[derive(Serialize, Deserialize, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct AddProjectParams {
+    pub project: Vec<ProjectJsonData>,
+}
+
 pub enum SyntaxTree {}
 
 impl Request for SyntaxTree {

crates/rust-analyzer/src/main_loop.rs

@@ -625,6 +625,7 @@ impl GlobalState {
             .on_sync_mut::<lsp_ext::ReloadWorkspace>(handlers::handle_workspace_reload)
             .on_sync_mut::<lsp_ext::MemoryUsage>(handlers::handle_memory_usage)
             .on_sync_mut::<lsp_ext::ShuffleCrateGraph>(handlers::handle_shuffle_crate_graph)
+            .on_sync_mut::<lsp_ext::AddProject>(handlers::handle_add_project)
             .on_sync::<lsp_ext::JoinLines>(handlers::handle_join_lines)
             .on_sync::<lsp_ext::OnEnter>(handlers::handle_on_enter)
             .on_sync::<lsp_types::request::SelectionRangeRequest>(handlers::handle_selection_range)