1 files changed, 109 insertions, 0 deletions

diff --git a/crates/ra_assists/src/handlers/generate_impl.rs b/crates/ra_assists/src/handlers/generate_impl.rs
new file mode 100644
index 000000000..d9b87c9c0
--- /dev/null
+++ b/crates/ra_assists/src/handlers/generate_impl.rs
@@ -0,0 +1,109 @@
+use ra_syntax::ast::{self, AstNode, GenericParamsOwner, NameOwner};
+use stdx::{format_to, SepBy};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_impl
+//
+// Adds a new inherent impl for a type.
+//
+// ```
+// struct Ctx<T: Clone> {
+//     data: T,<|>
+// }
+// ```
+// ->
+// ```
+// struct Ctx<T: Clone> {
+//     data: T,
+// }
+//
+// impl<T: Clone> Ctx<T> {
+//     $0
+// }
+// ```
+pub(crate) fn generate_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let nominal = ctx.find_node_at_offset::<ast::AdtDef>()?;
+    let name = nominal.name()?;
+    let target = nominal.syntax().text_range();
+    acc.add(
+        AssistId("generate_impl", AssistKind::Generate),
+        format!("Generate impl for `{}`", name),
+        target,
+        |edit| {
+            let type_params = nominal.generic_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_to!(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());
+
+                let generic_params = lifetime_params.chain(type_params).sep_by(", ");
+                format_to!(buf, "<{}>", generic_params)
+            }
+            match ctx.config.snippet_cap {
+                Some(cap) => {
+                    buf.push_str(" {\n    $0\n}");
+                    edit.insert_snippet(cap, start_offset, buf);
+                }
+                None => {
+                    buf.push_str(" {\n}");
+                    edit.insert(start_offset, buf);
+                }
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn test_add_impl() {
+        check_assist(
+            generate_impl,
+            "struct Foo {<|>}\n",
+            "struct Foo {}\n\nimpl Foo {\n    $0\n}\n",
+        );
+        check_assist(
+            generate_impl,
+            "struct Foo<T: Clone> {<|>}",
+            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n    $0\n}",
+        );
+        check_assist(
+            generate_impl,
+            "struct Foo<'a, T: Foo<'a>> {<|>}",
+            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n    $0\n}",
+        );
+    }
+
+    #[test]
+    fn add_impl_target() {
+        check_assist_target(
+            generate_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>> {}",
+        );
+    }
+}