Merge #5687

5687: Fix document symbols order r=matklad a=magurotuna

Resolves #5655 
And adds tests for `handle_document_symbol`, both with `hierarchical_symbols` enabled and with it disabled.

Previously document symbols were displayed in reverse order  in sublime text with its LSP plugin, but this patch fixes it like this:

![image](https://user-images.githubusercontent.com/23649474/89709020-fbccce00-d9b6-11ea-83b0-c88dc9f7977f.png)


Co-authored-by: Yusuke Tanaka <[email protected]>

1 files changed, 10 insertions, 5 deletions

diff --git a/crates/rust-analyzer/src/handlers.rs b/crates/rust-analyzer/src/handlers.rs
index e05ffc768..096127b0c 100644
--- a/crates/rust-analyzer/src/handlers.rs
+++ b/crates/rust-analyzer/src/handlers.rs
@@ -272,19 +272,24 @@ pub(crate) fn handle_document_symbol(
         parents.push((doc_symbol, symbol.parent));
     }
     let mut document_symbols = Vec::new();
+    // Constructs `document_symbols` from `parents`, in order from the end.
     while let Some((node, parent)) = parents.pop() {
         match parent {
             None => document_symbols.push(node),
             Some(i) => {
-                let children = &mut parents[i].0.children;
-                if children.is_none() {
-                    *children = Some(Vec::new());
-                }
-                children.as_mut().unwrap().push(node);
+                parents[i].0.children.get_or_insert_with(Vec::new).push(node);
             }
         }
     }
 
+    fn reverse(symbols: &mut Vec<DocumentSymbol>) {
+        for sym in symbols.iter_mut() {
+            sym.children.as_mut().map(|c| reverse(c));
+        }
+        symbols.reverse();
+    }
+    reverse(&mut document_symbols);
+
     let res = if snap.config.client_caps.hierarchical_symbols {
         document_symbols.into()
     } else {