Add derive intention

crates/libeditor/src/code_actions.rs

@@ -1,11 +1,12 @@
 use {TextUnit, File, EditBuilder, Edit};
 use libsyntax2::{
-    ast::AstNode,
+    ast::{self, AstNode},
     SyntaxKind::COMMA,
     SyntaxNodeRef,
+    SyntaxRoot,
     algo::{
         Direction, siblings,
-        find_leaf_at_offset,
+        find_leaf_at_offset, ancestors,
     },
 };
 
@@ -24,10 +25,32 @@ pub fn flip_comma<'a>(file: &'a File, offset: TextUnit) -> Option<impl FnOnce()
     })
 }
 
+pub fn add_derive<'a>(file: &'a File, offset: TextUnit) -> Option<impl FnOnce() -> Edit + 'a> {
+    let syntax = file.syntax();
+    let syntax = syntax.as_ref();
+    let nominal = find_node::<ast::NominalDef<_>>(syntax, offset)?;
+    Some(move || {
+        let mut edit = EditBuilder::new();
+        edit.insert(nominal.syntax().range().start(), "#[derive()]\n".to_string());
+        edit.finish()
+    })
+}
+
 fn non_trivia_sibling(node: SyntaxNodeRef, direction: Direction) -> Option<SyntaxNodeRef> {
     siblings(node, direction)
         .skip(1)
         .find(|node| !node.kind().is_trivia())
 }
 
+fn find_non_trivia_leaf(syntax: SyntaxNodeRef, offset: TextUnit) -> Option<SyntaxNodeRef> {
+    find_leaf_at_offset(syntax, offset)
+        .find(|leaf| !leaf.kind().is_trivia())
+}
+
+fn find_node<'a, N: AstNode<&'a SyntaxRoot>>(syntax: SyntaxNodeRef<'a>, offset: TextUnit) -> Option<N> {
+    let leaf = find_non_trivia_leaf(syntax, offset)?;
+    ancestors(leaf)
+        .filter_map(N::cast)
+        .next()
+}