1 files changed, 97 insertions, 0 deletions

diff --git a/crates/ra_editor/src/assists/add_derive.rs b/crates/ra_editor/src/assists/add_derive.rs
new file mode 100644
index 000000000..33d9d2c31
--- /dev/null
+++ b/crates/ra_editor/src/assists/add_derive.rs
@@ -0,0 +1,97 @@
+use ra_text_edit::TextEditBuilder;
+use ra_syntax::{
+    ast::{self, AstNode, AttrsOwner},
+    SourceFileNode,
+    SyntaxKind::{WHITESPACE, COMMENT},
+    TextUnit,
+};
+
+use crate::{
+    find_node_at_offset,
+    assists::LocalEdit,
+};
+
+pub fn add_derive<'a>(
+    file: &'a SourceFileNode,
+    offset: TextUnit,
+) -> Option<impl FnOnce() -> LocalEdit + 'a> {
+    let nominal = find_node_at_offset::<ast::NominalDef>(file.syntax(), offset)?;
+    let node_start = derive_insertion_offset(nominal)?;
+    return Some(move || {
+        let derive_attr = nominal
+            .attrs()
+            .filter_map(|x| x.as_call())
+            .filter(|(name, _arg)| name == "derive")
+            .map(|(_name, arg)| arg)
+            .next();
+        let mut edit = TextEditBuilder::new();
+        let offset = match derive_attr {
+            None => {
+                edit.insert(node_start, "#[derive()]\n".to_string());
+                node_start + TextUnit::of_str("#[derive(")
+            }
+            Some(tt) => tt.syntax().range().end() - TextUnit::of_char(')'),
+        };
+        LocalEdit {
+            label: "add `#[derive]`".to_string(),
+            edit: edit.finish(),
+            cursor_position: Some(offset),
+        }
+    });
+
+    // Insert `derive` after doc comments.
+    fn derive_insertion_offset(nominal: ast::NominalDef) -> Option<TextUnit> {
+        let non_ws_child = nominal
+            .syntax()
+            .children()
+            .find(|it| it.kind() != COMMENT && it.kind() != WHITESPACE)?;
+        Some(non_ws_child.range().start())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test_utils::check_action;
+
+    #[test]
+    fn add_derive_new() {
+        check_action(
+            "struct Foo { a: i32, <|>}",
+            "#[derive(<|>)]\nstruct Foo { a: i32, }",
+            |file, off| add_derive(file, off).map(|f| f()),
+        );
+        check_action(
+            "struct Foo { <|> a: i32, }",
+            "#[derive(<|>)]\nstruct Foo {  a: i32, }",
+            |file, off| add_derive(file, off).map(|f| f()),
+        );
+    }
+
+    #[test]
+    fn add_derive_existing() {
+        check_action(
+            "#[derive(Clone)]\nstruct Foo { a: i32<|>, }",
+            "#[derive(Clone<|>)]\nstruct Foo { a: i32, }",
+            |file, off| add_derive(file, off).map(|f| f()),
+        );
+    }
+
+    #[test]
+    fn add_derive_new_with_doc_comment() {
+        check_action(
+            "
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+struct Foo { a: i32<|>, }
+            ",
+            "
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+#[derive(<|>)]
+struct Foo { a: i32, }
+            ",
+            |file, off| add_derive(file, off).map(|f| f()),
+        );
+    }
+}