Add optional range parameter to SyntaxTreeParams

When range is provided, instead of showing the syntax for the whole file, we'll
show the syntax tree for the given range.

crates/ra_lsp_server/src/main_loop/handlers.rs

@@ -32,7 +32,9 @@ pub fn handle_analyzer_status(world: ServerWorld, _: ()) -> Result<String> {
 
 pub fn handle_syntax_tree(world: ServerWorld, params: req::SyntaxTreeParams) -> Result<String> {
     let id = params.text_document.try_conv_with(&world)?;
-    let res = world.analysis().syntax_tree(id);
+    let line_index = world.analysis().file_line_index(id);
+    let text_range = params.range.map(|p| p.conv_with(&line_index));
+    let res = world.analysis().syntax_tree(id, text_range);
     Ok(res)
 }
 

crates/ra_lsp_server/src/req.rs

@@ -39,6 +39,7 @@ impl Request for SyntaxTree {
 #[serde(rename_all = "camelCase")]
 pub struct SyntaxTreeParams {
     pub text_document: TextDocumentIdentifier,
+    pub range: Option<Range>,
 }
 
 pub enum ExtendSelection {}