feat: Add action to expand a declarative macro once, inline. Fixes #13598

[tfpk]

This commit adds a new r-a method, expandMacroInline, which expands the macro that's currently selected. See #13598 for the most applicable issue; though I suspect it'll resolve part of #5949 and make #11888 significantly easier).

The macro works like this:

I have 2 questions before this PR can be merged:

1. Should we rustfmt the output? The advantage of doing this is neater code. The disadvantages are we'd have to format the whole expr/stmt/block (since there's no point just formatting one part, especially over multiple lines), and maybe it moves the code around more in weird ways. My suggestion here is to start off by not doing any formatting; and if it appears useful we can decide to do formatting in a later release.
2. Is it worth solving the $crate hygiene issue now? -- I think this PR is usable as of right now for some use-cases; but it is annoying that many common macros (i.e. println!(), format!()) can't be expanded further unless the user guesses the correct $crate value. The trouble with solving that issue is that I think it's complicated and imperfect. If we do solve it; we'd also need to either change the existing expandMacro/expandMacroInline commands; provide some option to allow/disallow $crate expanding; or come to some other compromise.

[Veykril]

will take a proper look later but there is no need for this to be a custom command, it would make more sense to implement this as an assist instead
not formatting is okay right now, likewise not fixing the $crate replacement

[tfpk]

I'll push a commit to make this an assist (thanks -- didn't know that was an option). Is it worth having a command too to do a recursive inline?

I'll start working on replacing $crate as well and can do that as a separate PR.

[tfpk]

Just an update - the assist is almost done (just finishing off the tests). There's no point in reviewing most of this because it'll get reverted by changing it to be an assist. Thanks for your patience, and suggestions :)

[tfpk]

Okay @Veykril I think this is now ready for review. Thanks again :)

[Veykril]

Suggested change

	let tok = ctx.token_at_offset().right_biased()?;
	let mut anc = tok.parent_ancestors();
	let (_name, expanded, unexpanded) = loop {
	let node = anc.next()?;
	if let Some(mac) = ast::MacroCall::cast(node.clone()) {
	break (
	mac.path()?.segment()?.name_ref()?.to_string(),
	ctx.sema.expand(&mac)?.clone_for_update(),
	node,
	);
	}
	};
	let unexpanded = ctx.find_node_at_offset::<ast::MacroCall>()?;
	let expanded = ctx.sema.expand(&mac)?.clone_for_update();

[Veykril]

small nit, otherwise lgtm
@bors delegate+

[bors]

✌️ @tfpk can now approve this pull request

[Veykril]

@bors r+

[bors]

📌 Commit 769273c has been approved by Veykril

It is now in the queue for this repository.

[tfpk]

@Veykril is the CI failure above a known issue? A segfault in vscode doesn't seem like my issue, but wondering if we need to report or something?

[lnicola]

CC microsoft/vscode#101069

[bors]

⌛ Testing commit 769273c with merge 336608a...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 336608a to master...

[tfpk]

Is it worth adding this to the change log?

[Veykril]

This will appear on the next release changelog I believe

[lnicola]

Yeah, it will be featured automatically next Monday (as it was merged today, after the release).

[tfpk]

Ah, sorry! Didn't realise this happened after the release. Thanks so much:)

[jonas-schievink]

The gif should ideally have been updated to show that this is an assist, not a command

[lnicola]

I wanted to, but I have this little issue on my system:

inline-macro.mp4

[tfpk]

I can update the gif in the next half hour if that helps?

[tfpk]