Feature request: Inline type alias

[jplatte]

Similar to "Inline function" / "Inline into all callers", it would be nice if there was "Inline typealias" and "Inline into all uses" for type aliases.

[djc]

Was thinking about this yesterday, would’ve been nice for rustls/rustls#895.

[steven-joruk]

I'll try to implement this.

[0xPoe]

@Veykril It seems we can close this issue?

[steven-joruk]

Hey @hi-rustin, #11690 only added inlining a single instance of a type alias use, this feature also requests inlining the definition to all users.

[sancho20021]

I'm going to try this one

[sancho20021]

Hi @steven-joruk! Currently I'm trying to implement inline_alias_uses.

You added a nice test:

rust-analyzer/crates/ide-assists/src/handlers/inline_type_alias.rs

Lines 385 to 398 in 49700e4

	// This must be supported in order to support "inline_alias_to_users" or
	// whatever it will be called.
	#[test]
	fn alias_as_expression_ignored() {
	check_assist_not_applicable(
	inline_type_alias,
	r#"
	type A = Vec<u32>;
	fn main() {
	let a: A = $0A::new();
	}
	"#,
	);
	}

which shows that the current implementation can't inline such alias uses.

IIUC, this happens because ctx.find_node_at_offset::<ast::PathType>() invocation returns None, and we have no alias instance to work with.

Could you please explain, why ctx.find_node_at_offset behaves in such a way? This is my first issue in rust-analyzer so I have very little understanding of things 😄

[Veykril]

An ast::PathType specifically is an ast::Path that appreas in type position, as an example let PathPat: PathType = PathExpr;.

So to support inlining on usages, we should be checking ctx.find_note_at_offset::<ast::Path>(), then check the parent node of that path and act accordingly.

[sancho20021]

Besides calling an associated function on an aliased type, there seems to be a lot of other usages. (Enum variant, Record expression, etc)

What is more important that needs to be done first, cover as much usages as possible in inline_type_alias or implementing a basic version of inline_type_alias_uses that works only for PathType?

By the way, I'm not sure I understand, what does Path represent?

[Veykril]

A Path is just something like foo::bar::Baz or foo on its own as well. PathType, PathPat, PathExpr etc just wrap a Path then depending on whether it is a type, pattern expression

It doesnt really matter what you improve herefirst, thats up to you