Undo the previous mistaken change and make publish_decorations optional

See https://github.com/Microsoft/language-server-protocol/issues/567
for motivations to not require `InitializationOptions`

TODO: Check if there are any other protocol extensions
which should be disabled if not implemented on the client

crates/ra_lsp_server/src/main.rs

@@ -27,7 +27,10 @@ fn main() -> Result<()> {
 #[derive(Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct InitializationOptions {
-    highlighting_on: bool,
+    // Whether the client supports our custom highlighting publishing decorations.
+    // This is different to the highlightingOn setting, which is whether the client
+    // wants highlighting to be used or sent.
+    publish_decorations: Option<bool>,
 }
 
 fn main_inner() -> Result<()> {
@@ -42,12 +45,12 @@ fn main_inner() -> Result<()> {
                 .root_uri
                 .and_then(|it| it.to_file_path().ok())
                 .unwrap_or(cwd);
-            let publish_decorations = params
+            let supports_decorations = params
                 .initialization_options
                 .and_then(|v| InitializationOptions::deserialize(v).ok())
-                .map(|it| it.highlighting_on)
+                .and_then(|it| it.publish_decorations)
                 == Some(true);
-            ra_lsp_server::main_loop(false, root, publish_decorations, r, s)
+            ra_lsp_server::main_loop(false, root, supports_decorations, r, s)
         },
     )?;
     log::info!("shutting down IO...");

crates/ra_lsp_server/src/main_loop.rs

@@ -53,7 +53,7 @@ enum Task {
 pub fn main_loop(
     internal_mode: bool,
     ws_root: PathBuf,
-    publish_decorations: bool,
+    supports_decorations: bool,
     msg_receiver: &Receiver<RawMessage>,
     msg_sender: &Sender<RawMessage>,
 ) -> Result<()> {
@@ -82,7 +82,7 @@ pub fn main_loop(
     let mut subs = Subscriptions::new();
     let main_res = main_loop_inner(
         internal_mode,
-        publish_decorations,
+        supports_decorations,
         &pool,
         msg_sender,
         msg_receiver,
@@ -111,7 +111,7 @@ pub fn main_loop(
 
 fn main_loop_inner(
     internal_mode: bool,
-    publish_decorations: bool,
+    supports_decorations: bool,
     pool: &ThreadPool,
     msg_sender: &Sender<RawMessage>,
     msg_receiver: &Receiver<RawMessage>,
@@ -201,7 +201,7 @@ fn main_loop_inner(
             update_file_notifications_on_threadpool(
                 pool,
                 state.snapshot(),
-                publish_decorations,
+                supports_decorations,
                 task_sender.clone(),
                 subs.subscriptions(),
             )