Allow discoverBuckTargets with no documents

Summary: If given no documents, just immediately return the current set of projects. This essentially allows us to ask the server for the current set of projects. This is used in the next diff to support simultaneous editing in fbsource and aosp.

Reviewed By: Wilfred

Differential Revision: D55899017

fbshipit-source-id: 4d60264e6ae1ae3bc440fcfa5b538df87ce8a6a2

integrations/rust-project/src/server.rs

@@ -293,6 +293,11 @@ fn handle_discover_buck_targets(
     let State {
         server, projects, ..
     } = state;
+
+    if params.text_documents.is_empty() {
+        return Ok(DiscoverBuckTargetsResult::Many(projects.clone()));
+    }
+
     let develop = Develop::new();
 
     // this request is load-bearing: it is necessary in order to start showing in-editor progress.