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

use ra_syntax::{
    ast::{self, edit, make, AstNode, NameOwner, TypeBoundsOwner},
    SyntaxElement,
    SyntaxKind::*,
};

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

// Assist: move_bounds_to_where_clause
//
// Moves inline type bounds to a where clause.
//
// ```
// fn apply<T, U, <|>F: FnOnce(T) -> U>(f: F, x: T) -> U {
//     f(x)
// }
// ```
// ->
// ```
// fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
//     f(x)
// }
// ```
pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx) -> Option<Assist> {
    let type_param_list = ctx.find_node_at_offset::<ast::TypeParamList>()?;

    let mut type_params = type_param_list.type_params();
    if type_params.all(|p| p.type_bound_list().is_none()) {
        return None;
    }

    let parent = type_param_list.syntax().parent()?;
    if parent.children_with_tokens().any(|it| it.kind() == WHERE_CLAUSE) {
        return None;
    }

    let anchor: SyntaxElement = match parent.kind() {
        FN_DEF => ast::FnDef::cast(parent)?.body()?.syntax().clone().into(),
        TRAIT_DEF => ast::TraitDef::cast(parent)?.item_list()?.syntax().clone().into(),
        IMPL_BLOCK => ast::ImplBlock::cast(parent)?.item_list()?.syntax().clone().into(),
        ENUM_DEF => ast::EnumDef::cast(parent)?.variant_list()?.syntax().clone().into(),
        STRUCT_DEF => parent
            .children_with_tokens()
            .find(|it| it.kind() == RECORD_FIELD_DEF_LIST || it.kind() == SEMI)?,
        _ => return None,
    };

    ctx.add_assist(AssistId("move_bounds_to_where_clause"), "Move to where clause", |edit| {
        let new_params = type_param_list
            .type_params()
            .filter(|it| it.type_bound_list().is_some())
            .map(|type_param| {
                let without_bounds = type_param.remove_bounds();
                (type_param, without_bounds)
            });

        let new_type_param_list = edit::replace_descendants(&type_param_list, new_params);
        edit.replace_ast(type_param_list.clone(), new_type_param_list);

        let where_clause = {
            let predicates = type_param_list.type_params().filter_map(build_predicate);
            make::where_clause(predicates)
        };

        let to_insert = match anchor.prev_sibling_or_token() {
            Some(ref elem) if elem.kind() == WHITESPACE => format!("{} ", where_clause.syntax()),
            _ => format!(" {}", where_clause.syntax()),
        };
        edit.insert(anchor.text_range().start(), to_insert);
        edit.target(type_param_list.syntax().text_range());
    })
}

fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
    let path = {
        let name_ref = make::name_ref(&param.name()?.syntax().to_string());
        let segment = make::path_segment(name_ref);
        make::path_unqalified(segment)
    };
    let predicate = make::where_pred(path, param.type_bound_list()?.bounds());
    Some(predicate)
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::helpers::check_assist;

    #[test]
    fn move_bounds_to_where_clause_fn() {
        check_assist(
            move_bounds_to_where_clause,
            r#"
            fn foo<T: u32, <|>F: FnOnce(T) -> T>() {}
            "#,
            r#"
            fn foo<T, <|>F>() where T: u32, F: FnOnce(T) -> T {}
            "#,
        );
    }

    #[test]
    fn move_bounds_to_where_clause_impl() {
        check_assist(
            move_bounds_to_where_clause,
            r#"
            impl<U: u32, <|>T> A<U, T> {}
            "#,
            r#"
            impl<U, <|>T> A<U, T> where U: u32 {}
            "#,
        );
    }

    #[test]
    fn move_bounds_to_where_clause_struct() {
        check_assist(
            move_bounds_to_where_clause,
            r#"
            struct A<<|>T: Iterator<Item = u32>> {}
            "#,
            r#"
            struct A<<|>T> where T: Iterator<Item = u32> {}
            "#,
        );
    }

    #[test]
    fn move_bounds_to_where_clause_tuple_struct() {
        check_assist(
            move_bounds_to_where_clause,
            r#"
            struct Pair<<|>T: u32>(T, T);
            "#,
            r#"
            struct Pair<<|>T>(T, T) where T: u32;
            "#,
        );
    }
}