From 66be735aa98c32fb062d1c756fa9303ff2d13002 Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Sun, 12 Aug 2018 18:50:16 +0300
Subject: flip comma

---
 crates/libsyntax2/src/yellow/syntax.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'crates/libsyntax2/src/yellow/syntax.rs')

diff --git a/crates/libsyntax2/src/yellow/syntax.rs b/crates/libsyntax2/src/yellow/syntax.rs
index a22275ed9..00f76e51c 100644
--- a/crates/libsyntax2/src/yellow/syntax.rs
+++ b/crates/libsyntax2/src/yellow/syntax.rs
@@ -101,6 +101,17 @@ impl<R: TreeRoot> SyntaxNode<R> {
         })
     }
 
+    pub fn prev_sibling(&self) -> Option<SyntaxNode<R>> {
+        let red = self.red();
+        let parent = self.parent()?;
+        let prev_sibling_idx = red.index_in_parent()?.checked_sub(1)?;
+        let sibling_red = parent.red().get_child(prev_sibling_idx)?;
+        Some(SyntaxNode {
+            root: self.root.clone(),
+            red: sibling_red,
+        })
+    }
+
     pub fn is_leaf(&self) -> bool {
         self.first_child().is_none()
     }
-- 
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