Reorganize Document::apply_impl (#11304)

These changes are ported from
<https://redirect.github.com/helix-editor/helix/pull/9801>. It's a
cleanup of `Document::apply_impl` that uses some early returns to
reduce nesting and some reordering of the steps. The early returns
bail out of `apply_impl` early if the transaction fails to apply or
if the changes are empty (in which case we emit the SelectionDidChange
event). It's a somewhat cosmetic refactor that makes the function easier
to reason about but it also makes it harder to introduce bugs by mapping
positions through empty changesets for example.

Co-authored-by: Pascal Kuthe <pascalkuthe@pm.me>

helix-view/src/document.rs

@@ -1222,17 +1222,27 @@ impl Document {
         use helix_core::Assoc;
 
         let old_doc = self.text().clone();
+        let changes = transaction.changes();
+        if !changes.apply(&mut self.text) {
+            return false;
+        }
 
-        let success = transaction.changes().apply(&mut self.text);
-
-        if success {
-            if emit_lsp_notification {
-                helix_event::dispatch(DocumentDidChange {
+        if changes.is_empty() {
+            if let Some(selection) = transaction.selection() {
+                self.selections.insert(
+                    view_id,
+                    selection.clone().ensure_invariants(self.text.slice(..)),
+                );
+                helix_event::dispatch(SelectionDidChange {
                     doc: self,
                     view: view_id,
-                    old_text: &old_doc,
                 });
             }
+            return true;
+        }
+
+        self.modified_since_accessed = true;
+        self.version += 1;
 
         for selection in self.selections.values_mut() {
             *selection = selection
@@ -1249,28 +1259,6 @@ impl Document {
                 .map_pos(view_data.view_position.anchor, Assoc::Before);
         }
 
-            // if specified, the current selection should instead be replaced by transaction.selection
-            if let Some(selection) = transaction.selection() {
-                self.selections.insert(
-                    view_id,
-                    selection.clone().ensure_invariants(self.text.slice(..)),
-                );
-                helix_event::dispatch(SelectionDidChange {
-                    doc: self,
-                    view: view_id,
-                });
-            }
-
-            self.modified_since_accessed = true;
-        }
-
-        if !transaction.changes().is_empty() {
-            self.version += 1;
-            // start computing the diff in parallel
-            if let Some(diff_handle) = &self.diff_handle {
-                diff_handle.update_document(self.text.clone(), false);
-            }
-
         // generate revert to savepoint
         if !self.savepoints.is_empty() {
             let revert = transaction.invert(&old_doc);
@@ -1300,7 +1288,11 @@ impl Document {
             }
         }
 
-            let changes = transaction.changes();
+        // TODO: all of that should likely just be hooks
+        // start computing the diff in parallel
+        if let Some(diff_handle) = &self.diff_handle {
+            diff_handle.update_document(self.text.clone(), false);
+        }
 
         // map diagnostics over changes too
         changes.update_positions(self.diagnostics.iter_mut().map(|diagnostic| {
@@ -1334,9 +1326,8 @@ impl Document {
             true
         });
 
-            self.diagnostics.sort_by_key(|diagnostic| {
-                (diagnostic.range, diagnostic.severity, diagnostic.provider)
-            });
+        self.diagnostics
+            .sort_by_key(|diagnostic| (diagnostic.range, diagnostic.severity, diagnostic.provider));
 
         // Update the inlay hint annotations' positions, helping ensure they are displayed in the proper place
         let apply_inlay_hint_changes = |annotations: &mut Vec<InlineAnnotation>| {
@@ -1365,6 +1356,24 @@ impl Document {
             apply_inlay_hint_changes(padding_after_inlay_hints);
         }
 
+        helix_event::dispatch(DocumentDidChange {
+            doc: self,
+            view: view_id,
+            old_text: &old_doc,
+        });
+
+        // if specified, the current selection should instead be replaced by transaction.selection
+        if let Some(selection) = transaction.selection() {
+            self.selections.insert(
+                view_id,
+                selection.clone().ensure_invariants(self.text.slice(..)),
+            );
+            helix_event::dispatch(SelectionDidChange {
+                doc: self,
+                view: view_id,
+            });
+        }
+
         if emit_lsp_notification {
             // TODO: move to hook
             // emit lsp notification
@@ -1381,8 +1390,8 @@ impl Document {
                 }
             }
         }
-        }
-        success
+
+        true
     }
 
     fn apply_inner(