feat: Add the Hover Range capability which enables showing the type of an expression

[alexfertel]

Closes #389

This PR extends the textDocument/hover method to allow getting the type of an expression. It looks like this:

Edit: One thing I noticed is that when hovering a selection that includes a macro it doesn't work, so maybe this would need a follow-up issue discussing what problem that may have.

(PS: What a great project! I am learning a lot! 🚀)

[matklad]

Oh my, I didn't realise that it's possible to convince VS Code to actually use this! My original plan was to just implement this in the server and wait for emacs/vim to pick this up, and then bug vs code maintainers to follow the suite. You, however, managed to implement this in vscode, kudos!

[matklad]

Note that we already have a custom hover request (we customize the return type), so you only need to add custom params:

diff --git a/crates/rust-analyzer/src/handlers.rs b/crates/rust-analyzer/src/handlers.rs
index f89b7f5d7..8a115ec30 100644
--- a/crates/rust-analyzer/src/handlers.rs
+++ b/crates/rust-analyzer/src/handlers.rs
@@ -867,7 +867,7 @@ pub(crate) fn handle_signature_help(
 
 pub(crate) fn handle_hover(
     snap: GlobalStateSnapshot,
-    params: lsp_types::HoverParams,
+    params: lsp_ext::HoverParams,
 ) -> Result<Option<lsp_ext::Hover>> {
     let _p = profile::span("handle_hover");
     let position = from_proto::file_position(&snap, params.text_document_position_params)?;
diff --git a/crates/rust-analyzer/src/lsp_ext.rs b/crates/rust-analyzer/src/lsp_ext.rs
index 7aed93f99..627cacc9c 100644
--- a/crates/rust-analyzer/src/lsp_ext.rs
+++ b/crates/rust-analyzer/src/lsp_ext.rs
@@ -376,24 +376,25 @@ pub struct SnippetTextEdit {
 pub enum HoverRequest {}
 
 impl Request for HoverRequest {
-    type Params = lsp_types::HoverParams;
+    type Params = HoverParams;
     type Result = Option<Hover>;
     const METHOD: &'static str = "textDocument/hover";
 }
 
-pub enum HoverRangeRequest {}
-
-impl Request for HoverRangeRequest {
-    type Params = HoverRangeParams;
-    type Result = Option<Hover>;
-    const METHOD: &'static str = "rust-analyzer/hoverRange";
-}
-
-#[derive(Deserialize, Serialize, Debug)]
+#[derive(Debug, Eq, PartialEq, Clone, Deserialize, Serialize)]
 #[serde(rename_all = "camelCase")]
-pub struct HoverRangeParams {
+pub struct HoverParams {
     pub text_document: TextDocumentIdentifier,
-    pub range: Range,
+    pub position: PositionOrRange,
+    #[serde(flatten)]
+    pub work_done_progress_params: WorkDoneProgressParams,
+}
+
+#[derive(Debug, Eq, PartialEq, Clone, Deserialize, Serialize)]
+#[serde(untagged)]
+enum PositionOrRange {
+    Position(lsp_types::Position),
+    Range(lsp_types::Range),
 }
 
 #[derive(Debug, PartialEq, Clone, Deserialize, Serialize)]

[matklad]

And don't forget to document the extension in the lsp-extensions.md and add a corresponding server capability for it.

[alexfertel]

Note that we already have a custom hover request (we customize the return type), so you only need to add custom params:

This is it!!! My god, I struggled so much because I thought the name of the param had to change 😭

Thanks for the quick response! I'll try to revisit this today 😁

[flodiebold]

If it's just an extension to the existing hover request, I think this should be very easy to add in Emacs as well.

[alexfertel]

@matklad I think this is fairly complete :) No clue on how to approach adding the client/server capability 😅 Halp!

[matklad]

This needs to use only two slashes, otherwise it won't be picked up by our docgen infra.

[matklad]

Rather than adding a second function, let's change the existing one to take a range, and let's use empty range for the case where the input is a single position.

[matklad]

This should have **Experimental Server Capability:** { "hoverRange": boolean }, see how thouse are defiened for some other requests in this file.

[matklad]

You'll want to add an actual capability to https://github.com/rust-analyzer/rust-analyzer/blob/3a59b56324db99475ea2027cb94f82785b16ad14/crates/rust-analyzer/src/caps.rs#L115-L125

[matklad]

bors r+

[bors]

Build succeeded:

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

[lnicola]

Not exactly, but...

changelog feat (first contribution) add "Hover Range" capability to get the type of an expression

[simrat39]

Can the hover response have actions (hover actions) attached to them? I guess not since its only the value of an expression.

[Veykril]

That should be doable just fine since we show a type we can show type hover actions, done with #9856