Feat: LSP Type Hints (#5934)

* misc: missing inline, outdated link

* doc: Add new theme keys and config option to book

* fix: don't panic in Tree::try_get(view_id)

Necessary for later, where we could be receiving an LSP response
for a closed window, in which case we don't want to crash while
checking for its existence

* fix: reset idle timer on all mouse events

* refacto: Introduce Overlay::new and InlineAnnotation::new

* refacto: extract make_job_callback from Context::callback

* feat: add LSP display_inlay_hint option to config

* feat: communicate inlay hints support capabilities of helix to LSP server

* feat: Add function to request range of inlay hint from LSP

* feat: Save inlay hints in document, per view

* feat: Update inlay hints on document changes

* feat: Compute inlay hints on idle timeout

* nit: Add todo's about inlay hints for later

* fix: compute text annotations for current view in view.rs, not document.rs

* doc: Improve Document::text_annotations() description

* nit: getters don't use 'get_' in front

* fix: Drop inlay hints annotations on config refresh if necessary

* fix: padding theming for LSP inlay hints

* fix: tracking of outdated inlay hints should not be dependant on document revision (because of undos and such)

* fix: follow LSP spec and don't highlight padding as virtual text

* config: add some LSP inlay hint configs

4 files changed, 212 insertions, 14 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 803f4051..1c1edece 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -114,17 +114,7 @@ impl<'a> Context<'a> {
         T: for<'de> serde::Deserialize<'de> + Send + 'static,
         F: FnOnce(&mut Editor, &mut Compositor, T) + Send + 'static,
     {
-        let callback = Box::pin(async move {
-            let json = call.await?;
-            let response = serde_json::from_value(json)?;
-            let call: job::Callback = Callback::EditorCompositor(Box::new(
-                move |editor: &mut Editor, compositor: &mut Compositor| {
-                    callback(editor, compositor, response)
-                },
-            ));
-            Ok(call)
-        });
-        self.jobs.callback(callback);
+        self.jobs.callback(make_job_callback(call, callback));
     }
 
     /// Returns 1 if no explicit count was provided
@@ -134,6 +124,27 @@ impl<'a> Context<'a> {
     }
 }
 
+#[inline]
+fn make_job_callback<T, F>(
+    call: impl Future<Output = helix_lsp::Result<serde_json::Value>> + 'static + Send,
+    callback: F,
+) -> std::pin::Pin<Box<impl Future<Output = Result<Callback, anyhow::Error>>>>
+where
+    T: for<'de> serde::Deserialize<'de> + Send + 'static,
+    F: FnOnce(&mut Editor, &mut Compositor, T) + Send + 'static,
+{
+    Box::pin(async move {
+        let json = call.await?;
+        let response = serde_json::from_value(json)?;
+        let call: job::Callback = Callback::EditorCompositor(Box::new(
+            move |editor: &mut Editor, compositor: &mut Compositor| {
+                callback(editor, compositor, response)
+            },
+        ));
+        Ok(call)
+    })
+}
+
 use helix_view::{align_view, Align};
 
 /// A MappableCommand is either a static command like "jump_view_up" or a Typable command like
diff --git a/helix-term/src/commands/lsp.rs b/helix-term/src/commands/lsp.rs
index 08519366..f9d9856f 100644
--- a/helix-term/src/commands/lsp.rs
+++ b/helix-term/src/commands/lsp.rs
@@ -15,8 +15,13 @@ use tui::{
 
 use super::{align_view, push_jump, Align, Context, Editor, Open};
 
-use helix_core::{path, Selection};
-use helix_view::{document::Mode, editor::Action, theme::Style};
+use helix_core::{path, text_annotations::InlineAnnotation, Selection};
+use helix_view::{
+    document::{DocumentInlayHints, DocumentInlayHintsId, Mode},
+    editor::Action,
+    theme::Style,
+    Document, View,
+};
 
 use crate::{
     compositor::{self, Compositor},
@@ -27,7 +32,8 @@ use crate::{
 };
 
 use std::{
-    borrow::Cow, cmp::Ordering, collections::BTreeMap, fmt::Write, path::PathBuf, sync::Arc,
+    borrow::Cow, cmp::Ordering, collections::BTreeMap, fmt::Write, future::Future, path::PathBuf,
+    sync::Arc,
 };
 
 /// Gets the language server that is attached to a document, and
@@ -1391,3 +1397,174 @@ pub fn select_references_to_symbol_under_cursor(cx: &mut Context) {
         },
     );
 }
+
+pub fn compute_inlay_hints_for_all_views(editor: &mut Editor, jobs: &mut crate::job::Jobs) {
+    if !editor.config().lsp.display_inlay_hints {
+        return;
+    }
+
+    for (view, _) in editor.tree.views() {
+        let doc = match editor.documents.get(&view.doc) {
+            Some(doc) => doc,
+            None => continue,
+        };
+        if let Some(callback) = compute_inlay_hints_for_view(view, doc) {
+            jobs.callback(callback);
+        }
+    }
+}
+
+fn compute_inlay_hints_for_view(
+    view: &View,
+    doc: &Document,
+) -> Option<std::pin::Pin<Box<impl Future<Output = Result<crate::job::Callback, anyhow::Error>>>>> {
+    let view_id = view.id;
+    let doc_id = view.doc;
+
+    let language_server = doc.language_server()?;
+
+    let capabilities = language_server.capabilities();
+
+    let (future, new_doc_inlay_hints_id) = match capabilities.inlay_hint_provider {
+        Some(
+            lsp::OneOf::Left(true)
+            | lsp::OneOf::Right(lsp::InlayHintServerCapabilities::Options(_)),
+        ) => {
+            let doc_text = doc.text();
+            let len_lines = doc_text.len_lines();
+
+            // Compute ~3 times the current view height of inlay hints, that way some scrolling
+            // will not show half the view with hints and half without while still being faster
+            // than computing all the hints for the full file (which could be dozens of time
+            // longer than the view is).
+            let view_height = view.inner_height();
+            let first_visible_line = doc_text.char_to_line(view.offset.anchor);
+            let first_line = first_visible_line.saturating_sub(view_height);
+            let last_line = first_visible_line
+                .saturating_add(view_height.saturating_mul(2))
+                .min(len_lines);
+
+            let new_doc_inlay_hint_id = DocumentInlayHintsId {
+                first_line,
+                last_line,
+            };
+            // Don't recompute the annotations in case nothing has changed about the view
+            if !doc.inlay_hints_oudated
+                && doc
+                    .inlay_hints(view_id)
+                    .map_or(false, |dih| dih.id == new_doc_inlay_hint_id)
+            {
+                return None;
+            }
+
+            let doc_slice = doc_text.slice(..);
+            let first_char_in_range = doc_slice.line_to_char(first_line);
+            let last_char_in_range = doc_slice.line_to_char(last_line);
+
+            let range = helix_lsp::util::range_to_lsp_range(
+                doc_text,
+                helix_core::Range::new(first_char_in_range, last_char_in_range),
+                language_server.offset_encoding(),
+            );
+
+            (
+                language_server.text_document_range_inlay_hints(doc.identifier(), range, None),
+                new_doc_inlay_hint_id,
+            )
+        }
+        _ => return None,
+    };
+
+    let callback = super::make_job_callback(
+        future?,
+        move |editor, _compositor, response: Option<Vec<lsp::InlayHint>>| {
+            // The config was modified or the window was closed while the request was in flight
+            if !editor.config().lsp.display_inlay_hints || editor.tree.try_get(view_id).is_none() {
+                return;
+            }
+
+            // Add annotations to relevant document, not the current one (it may have changed in between)
+            let doc = match editor.documents.get_mut(&doc_id) {
+                Some(doc) => doc,
+                None => return,
+            };
+
+            // If we have neither hints nor an LSP, empty the inlay hints since they're now oudated
+            let (mut hints, offset_encoding) = match (response, doc.language_server()) {
+                (Some(h), Some(ls)) if !h.is_empty() => (h, ls.offset_encoding()),
+                _ => {
+                    doc.set_inlay_hints(
+                        view_id,
+                        DocumentInlayHints::empty_with_id(new_doc_inlay_hints_id),
+                    );
+                    doc.inlay_hints_oudated = false;
+                    return;
+                }
+            };
+
+            // Most language servers will already send them sorted but ensure this is the case to
+            // avoid errors on our end.
+            hints.sort_unstable_by_key(|inlay_hint| inlay_hint.position);
+
+            let mut padding_before_inlay_hints = Vec::new();
+            let mut type_inlay_hints = Vec::new();
+            let mut parameter_inlay_hints = Vec::new();
+            let mut other_inlay_hints = Vec::new();
+            let mut padding_after_inlay_hints = Vec::new();
+
+            let doc_text = doc.text();
+
+            for hint in hints {
+                let char_idx =
+                    match helix_lsp::util::lsp_pos_to_pos(doc_text, hint.position, offset_encoding)
+                    {
+                        Some(pos) => pos,
+                        // Skip inlay hints that have no "real" position
+                        None => continue,
+                    };
+
+                let label = match hint.label {
+                    lsp::InlayHintLabel::String(s) => s,
+                    lsp::InlayHintLabel::LabelParts(parts) => parts
+                        .into_iter()
+                        .map(|p| p.value)
+                        .collect::<Vec<_>>()
+                        .join(""),
+                };
+
+                let inlay_hints_vec = match hint.kind {
+                    Some(lsp::InlayHintKind::TYPE) => &mut type_inlay_hints,
+                    Some(lsp::InlayHintKind::PARAMETER) => &mut parameter_inlay_hints,
+                    // We can't warn on unknown kind here since LSPs are free to set it or not, for
+                    // example Rust Analyzer does not: every kind will be `None`.
+                    _ => &mut other_inlay_hints,
+                };
+
+                if let Some(true) = hint.padding_left {
+                    padding_before_inlay_hints.push(InlineAnnotation::new(char_idx, " "));
+                }
+
+                inlay_hints_vec.push(InlineAnnotation::new(char_idx, label));
+
+                if let Some(true) = hint.padding_right {
+                    padding_after_inlay_hints.push(InlineAnnotation::new(char_idx, " "));
+                }
+            }
+
+            doc.set_inlay_hints(
+                view_id,
+                DocumentInlayHints {
+                    id: new_doc_inlay_hints_id,
+                    type_inlay_hints: type_inlay_hints.into(),
+                    parameter_inlay_hints: parameter_inlay_hints.into(),
+                    other_inlay_hints: other_inlay_hints.into(),
+                    padding_before_inlay_hints: padding_before_inlay_hints.into(),
+                    padding_after_inlay_hints: padding_after_inlay_hints.into(),
+                },
+            );
+            doc.inlay_hints_oudated = false;
+        },
+    );
+
+    Some(callback)
+}
diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 4abbe01e..7c22df74 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -990,6 +990,8 @@ impl EditorView {
     }
 
     pub fn handle_idle_timeout(&mut self, cx: &mut commands::Context) -> EventResult {
+        commands::compute_inlay_hints_for_all_views(cx.editor, cx.jobs);
+
         if let Some(completion) = &mut self.completion {
             return if completion.ensure_item_resolved(cx) {
                 EventResult::Consumed(None)
@@ -1014,6 +1016,10 @@ impl EditorView {
         event: &MouseEvent,
         cxt: &mut commands::Context,
     ) -> EventResult {
+        if event.kind != MouseEventKind::Moved {
+            cxt.editor.reset_idle_timer();
+        }
+
         let config = cxt.editor.config();
         let MouseEvent {
             kind,
diff --git a/helix-term/src/ui/picker.rs b/helix-term/src/ui/picker.rs
index ec8b1c7f..bc2f98ee 100644
--- a/helix-term/src/ui/picker.rs
+++ b/helix-term/src/ui/picker.rs
@@ -225,6 +225,9 @@ impl<T: Item> FilePicker<T> {
                 let loader = cx.editor.syn_loader.clone();
                 doc.detect_language(loader);
             }
+
+            // QUESTION: do we want to compute inlay hints in pickers too ? Probably not for now
+            // but it could be interesting in the future
         }
 
         EventResult::Consumed(None)
@@ -339,6 +342,7 @@ impl<T: Item + 'static> Component for FilePicker<T> {
                 inner,
                 doc,
                 offset,
+                // TODO: compute text annotations asynchronously here (like inlay hints)
                 &TextAnnotations::default(),
                 highlights,
                 &cx.editor.theme,