flip comma

crates/libeditor/src/code_actions.rs

@@ -0,0 +1,33 @@
+use {TextUnit, File, EditBuilder, Edit};
+use libsyntax2::{
+    ast::AstNode,
+    SyntaxKind::COMMA,
+    SyntaxNodeRef,
+    algo::{
+        Direction, siblings,
+        find_leaf_at_offset,
+    },
+};
+
+pub fn flip_comma<'a>(file: &'a File, offset: TextUnit) -> Option<impl FnOnce() -> Edit + 'a> {
+    let syntax = file.syntax();
+    let syntax = syntax.as_ref();
+
+    let comma = find_leaf_at_offset(syntax, offset).find(|leaf| leaf.kind() == COMMA)?;
+    let left = non_trivia_sibling(comma, Direction::Backward)?;
+    let right = non_trivia_sibling(comma, Direction::Forward)?;
+    Some(move || {
+        let mut edit = EditBuilder::new();
+        edit.replace(left.range(), right.text());
+        edit.replace(right.range(), left.text());
+        edit.finish()
+    })
+}
+
+fn non_trivia_sibling(node: SyntaxNodeRef, direction: Direction) -> Option<SyntaxNodeRef> {
+    siblings(node, direction)
+        .skip(1)
+        .find(|node| !node.kind().is_trivia())
+}
+
+