ide_assists/handlers/
introduce_named_generic.rs

use ide_db::syntax_helpers::suggest_name;
use itertools::Itertools;
use syntax::ast::{self, syntax_factory::SyntaxFactory, AstNode, HasGenericParams, HasName};

use crate::{AssistContext, AssistId, AssistKind, Assists};

// Assist: introduce_named_generic
//
// Replaces `impl Trait` function argument with the named generic.
//
// ```
// fn foo(bar: $0impl Bar) {}
// ```
// ->
// ```
// fn foo<$0B: Bar>(bar: B) {}
// ```
pub(crate) fn introduce_named_generic(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let impl_trait_type = ctx.find_node_at_offset::<ast::ImplTraitType>()?;
    let param = impl_trait_type.syntax().ancestors().find_map(ast::Param::cast)?;
    let fn_ = param.syntax().ancestors().find_map(ast::Fn::cast)?;

    let type_bound_list = impl_trait_type.type_bound_list()?;

    let make = SyntaxFactory::new();
    let target = fn_.syntax().text_range();
    acc.add(
        AssistId("introduce_named_generic", AssistKind::RefactorRewrite),
        "Replace impl trait with generic",
        target,
        |builder| {
            let mut editor = builder.make_editor(fn_.syntax());

            let existing_names = match fn_.generic_param_list() {
                Some(generic_param_list) => generic_param_list
                    .generic_params()
                    .flat_map(|param| match param {
                        ast::GenericParam::TypeParam(t) => t.name().map(|name| name.to_string()),
                        p => Some(p.to_string()),
                    })
                    .collect_vec(),
                None => Vec::new(),
            };
            let type_param_name = suggest_name::NameGenerator::new_with_names(
                existing_names.iter().map(|s| s.as_str()),
            )
            .for_impl_trait_as_generic(&impl_trait_type);

            let type_param = make.type_param(make.name(&type_param_name), Some(type_bound_list));
            let new_ty = make.ty(&type_param_name);

            editor.replace(impl_trait_type.syntax(), new_ty.syntax());
            editor.add_generic_param(&fn_, type_param.clone().into());

            if let Some(cap) = ctx.config.snippet_cap {
                editor.add_annotation(type_param.syntax(), builder.make_tabstop_before(cap));
            }

            editor.add_mappings(make.finish_with_mappings());
            builder.add_file_edits(ctx.file_id(), editor);
        },
    )
}

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

    use crate::tests::check_assist;

    #[test]
    fn introduce_named_generic_params() {
        check_assist(
            introduce_named_generic,
            r#"fn foo<G>(bar: $0impl Bar) {}"#,
            r#"fn foo<G, $0B: Bar>(bar: B) {}"#,
        );
    }

    #[test]
    fn replace_impl_trait_without_generic_params() {
        check_assist(
            introduce_named_generic,
            r#"fn foo(bar: $0impl Bar) {}"#,
            r#"fn foo<$0B: Bar>(bar: B) {}"#,
        );
    }

    #[test]
    fn replace_two_impl_trait_with_generic_params() {
        check_assist(
            introduce_named_generic,
            r#"fn foo<G>(foo: impl Foo, bar: $0impl Bar) {}"#,
            r#"fn foo<G, $0B: Bar>(foo: impl Foo, bar: B) {}"#,
        );
    }

    #[test]
    fn replace_impl_trait_with_empty_generic_params() {
        check_assist(
            introduce_named_generic,
            r#"fn foo<>(bar: $0impl Bar) {}"#,
            r#"fn foo<$0B: Bar>(bar: B) {}"#,
        );
    }

    #[test]
    fn replace_impl_trait_with_empty_multiline_generic_params() {
        check_assist(
            introduce_named_generic,
            r#"
fn foo<
>(bar: $0impl Bar) {}
"#,
            r#"
fn foo<$0B: Bar
>(bar: B) {}
"#,
        );
    }

    #[test]
    fn replace_impl_trait_with_exist_generic_letter() {
        check_assist(
            introduce_named_generic,
            r#"fn foo<B>(bar: $0impl Bar) {}"#,
            r#"fn foo<B, $0B1: Bar>(bar: B1) {}"#,
        );
    }

    #[test]
    fn replace_impl_trait_with_more_exist_generic_letter() {
        check_assist(
            introduce_named_generic,
            r#"fn foo<B, B0, B1, B3>(bar: $0impl Bar) {}"#,
            r#"fn foo<B, B0, B1, B3, $0B4: Bar>(bar: B4) {}"#,
        );
    }

    #[test]
    fn replace_impl_trait_with_multiline_generic_params() {
        check_assist(
            introduce_named_generic,
            r#"
fn foo<
    G: Foo,
    F,
    H,
>(bar: $0impl Bar) {}
"#,
            r#"
fn foo<
    G: Foo,
    F,
    H, $0B: Bar,
>(bar: B) {}
"#,
        );
    }

    #[test]
    fn replace_impl_trait_multiple() {
        check_assist(
            introduce_named_generic,
            r#"fn foo(bar: $0impl Foo + Bar) {}"#,
            r#"fn foo<$0F: Foo + Bar>(bar: F) {}"#,
        );
    }

    #[test]
    fn replace_impl_with_mut() {
        check_assist(
            introduce_named_generic,
            r#"fn f(iter: &mut $0impl Iterator<Item = i32>) {}"#,
            r#"fn f<$0I: Iterator<Item = i32>>(iter: &mut I) {}"#,
        );
    }

    #[test]
    fn replace_impl_inside() {
        check_assist(
            introduce_named_generic,
            r#"fn f(x: &mut Vec<$0impl Iterator<Item = i32>>) {}"#,
            r#"fn f<$0I: Iterator<Item = i32>>(x: &mut Vec<I>) {}"#,
        );
    }
}
ide_assists/handlers/introduce_named_generic.rs

ide_assists/handlers/
introduce_named_generic.rs
