rust/crates/ra_assists/src/handlers/add_impl.rs

use ra_syntax::{
    ast::{self, AstNode, NameOwner, TypeParamsOwner},
    TextSize,
};
use stdx::{format_to, SepBy};

use crate::{Assist, AssistCtx, AssistId};

// Assist: add_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> {
//
// }
// ```
pub(crate) fn add_impl(ctx: AssistCtx) -> Option<Assist> {
    let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
    let name = nominal.name()?;
    let target = nominal.syntax().text_range();
    ctx.add_assist(
        AssistId("add_impl"),
        format!("Implement {}", name.text().as_str()),
        target,
        |edit| {
            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_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)
            }
            buf.push_str(" {\n");
            edit.set_cursor(start_offset + TextSize::of(&buf));
            buf.push_str("\n}");
            edit.insert(start_offset, buf);
        },
    )
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::tests::{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>> {}",
        );
    }
}