feat: Add an assist for inlining type aliases

[steven-joruk]

I'm working towards implementing #10881, but I'd like to get this in first with earlier feedback.

Is inline_type_alias a good enough name? I guess the follow up assist would be called inline_type_alias_into_all_users based on that.

[Veykril]

Is inline_type_alias a good enough name? I guess the follow up assist would be called inline_type_alias_into_all_users based on that.

We'll go with similarity to inline call which has inline_call and inline_into_callers, so inline_type_alias and inline_type_alias_uses I'd say.

[steven-joruk]

Thanks for the review :), splitting up the function lead to some more improvements as well.

[Veykril]

Let's move this into the builder closure except for the early return.

[steven-joruk]

There are two more early exits for LifetimeMap::new and ConstAndTypeMap::new. Would you prefer this?

    enum Replacement {
        Generic { lifetime_map: LifetimeMap, const_and_type_map: ConstAndTypeMap },
        Plain,
    }

    let replacement = if let Some(alias_generics) = alias.generic_param_list() {
        if alias_generics.generic_params().next().is_none() {
            cov_mark::hit!(no_generics_params);
            return None;
        }

        let instance_args =
            alias_instance.syntax().descendants().find_map(ast::GenericArgList::cast);

        Replacement::Generic {
            lifetime_map: LifetimeMap::new(&instance_args, &alias_generics)?,
            const_and_type_map: ConstAndTypeMap::new(&instance_args, &alias_generics)?,
        }
    } else {
        Replacement::Plain
    };

    let target = alias_instance.syntax().text_range();

    acc.add(
        AssistId("inline_type_alias", AssistKind::RefactorInline),
        "Inline type alias",
        target,
        |builder| {
            let replacement_text = match replacement {
                Replacement::Generic { lifetime_map, const_and_type_map } => {
                    create_replacement(&lifetime_map, &const_and_type_map, &concrete_type)
                }
                Replacement::Plain => concrete_type.to_string(),
            };

            builder.replace(target, replacement_text);
        },
    )

[Veykril]

Ye that would work

[Veykril]

bors r+

[bors]

Build succeeded:

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)