1 files changed, 77 insertions, 0 deletions

diff --git a/crates/ra_assists/src/assists/add_impl.rs b/crates/ra_assists/src/assists/add_impl.rs
new file mode 100644
index 000000000..4b61f4031
--- /dev/null
+++ b/crates/ra_assists/src/assists/add_impl.rs
@@ -0,0 +1,77 @@
+use format_buf::format;
+use hir::db::HirDatabase;
+use join_to_string::join;
+use ra_syntax::{
+    ast::{self, AstNode, NameOwner, TypeParamsOwner},
+    TextUnit,
+};
+
+use crate::{Assist, AssistCtx, AssistId};
+
+pub(crate) fn add_impl(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
+    let name = nominal.name()?;
+    ctx.add_action(AssistId("add_impl"), "add impl", |edit| {
+        edit.target(nominal.syntax().text_range());
+        let type_params = nominal.type_param_list();
+        let start_offset = nominal.syntax().text_range().end();
+        let mut buf = String::new();
+        buf.push_str("\n\nimpl");
+        if let Some(type_params) = &type_params {
+            format!(buf, "{}", type_params.syntax());
+        }
+        buf.push_str(" ");
+        buf.push_str(name.text().as_str());
+        if let Some(type_params) = type_params {
+            let lifetime_params = type_params
+                .lifetime_params()
+                .filter_map(|it| it.lifetime_token())
+                .map(|it| it.text().clone());
+            let type_params =
+                type_params.type_params().filter_map(|it| it.name()).map(|it| it.text().clone());
+            join(lifetime_params.chain(type_params)).surround_with("<", ">").to_buf(&mut buf);
+        }
+        buf.push_str(" {\n");
+        edit.set_cursor(start_offset + TextUnit::of_str(&buf));
+        buf.push_str("\n}");
+        edit.insert(start_offset, buf);
+    });
+
+    ctx.build()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::helpers::{check_assist, check_assist_target};
+
+    #[test]
+    fn test_add_impl() {
+        check_assist(add_impl, "struct Foo {<|>}\n", "struct Foo {}\n\nimpl Foo {\n<|>\n}\n");
+        check_assist(
+            add_impl,
+            "struct Foo<T: Clone> {<|>}",
+            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n<|>\n}",
+        );
+        check_assist(
+            add_impl,
+            "struct Foo<'a, T: Foo<'a>> {<|>}",
+            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n<|>\n}",
+        );
+    }
+
+    #[test]
+    fn add_impl_target() {
+        check_assist_target(
+            add_impl,
+            "
+struct SomeThingIrrelevant;
+/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {<|>}
+struct EvenMoreIrrelevant;
+",
+            "/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {}",
+        );
+    }
+}