Merge #9693

9693: feat: Add the Hover Range capability which enables showing the type of an expression r=matklad a=alexfertel

Closes https://github.com/rust-analyzer/rust-analyzer/issues/389

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

![type_of_expression](https://user-images.githubusercontent.com/22298999/126914293-0ce49a92-545d-4005-a59e-9294fa2330d6.gif)

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! 🚀)

Co-authored-by: Alexander Gonzalez <alexfertel97@gmail.com>
Co-authored-by: Alexander González <alexfertel97@gmail.com>

crates/rust-analyzer/src/handlers.rs

@@ -36,7 +36,10 @@ use crate::{
     from_proto,
     global_state::{GlobalState, GlobalStateSnapshot},
     line_index::LineEndings,
-    lsp_ext::{self, InlayHint, InlayHintsParams, ViewCrateGraphParams, WorkspaceSymbolParams},
+    lsp_ext::{
+        self, InlayHint, InlayHintsParams, PositionOrRange, ViewCrateGraphParams,
+        WorkspaceSymbolParams,
+    },
     lsp_utils::all_edits_are_disjoint,
     to_proto, LspError, Result,
 };
@@ -867,15 +870,21 @@ 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)?;
-    let info = match snap.analysis.hover(&snap.config.hover(), position)? {
+    let range = match params.position {
+        PositionOrRange::Position(position) => Range::new(position, position),
+        PositionOrRange::Range(range) => range,
+    };
+
+    let file_range = from_proto::file_range(&snap, params.text_document, range)?;
+    let info = match snap.analysis.hover(&snap.config.hover(), file_range)? {
         None => return Ok(None),
         Some(info) => info,
     };
-    let line_index = snap.file_line_index(position.file_id)?;
+
+    let line_index = snap.file_line_index(file_range.file_id)?;
     let range = to_proto::range(&line_index, info.range);
     let hover = lsp_ext::Hover {
         hover: lsp_types::Hover {