Invalidate Visible Range, Responsive Language Update (#238)

### Description

- Updates the visible set of indices when text storage happens, fixing
the linked issue.
- When setting a new language on the highlighter, adds a small "reset"
that clears all current highlights. This makes the language update feel
snappier, as the user receives immediate feedback. Before the ts parser
could take a few seconds to begin highlighting, so there would be a
delay making it seem like the language update was not happening.
- Adds a missing `throw` to the tree-sitter client that made edits
always run synchronously (didn't feel big enough for a whole PR, found
while debugging).
- Only updates the font if the font is new, making text layouts occur
much less frequently (also doesn't feel big enough for a separate PR)

### Related Issues

* #235 

### Checklist

- [x] I read and understood the [contributing
guide](https://github.com/CodeEditApp/CodeEdit/blob/main/CONTRIBUTING.md)
as well as the [code of
conduct](https://github.com/CodeEditApp/CodeEdit/blob/main/CODE_OF_CONDUCT.md)
- [x] The issues this PR addresses are related to each other
- [x] My changes generate no new warnings
- [x] My code builds and runs on my machine
- [x] My changes are all related to the related issue above
- [x] I documented my code

### Screenshots



https://github.com/CodeEditApp/CodeEditSourceEditor/assets/35942988/e719178e-bc9a-4830-9ca5-8d113dcb9d8b

Sources/CodeEditSourceEditor/CodeEditSourceEditor.swift

@@ -156,12 +156,16 @@ public struct CodeEditSourceEditor: NSViewControllerRepresentable {
             return
         }
 
-        controller.font = font
+        if controller.font != font {
+            controller.font = font
+        }
+
         controller.wrapLines = wrapLines
         controller.useThemeBackground = useThemeBackground
         controller.lineHeightMultiple = lineHeight
         controller.editorOverscroll = editorOverscroll
         controller.contentInsets = contentInsets
+
         if controller.isEditable != isEditable {
             controller.isEditable = isEditable
         }
@@ -173,15 +177,19 @@ public struct CodeEditSourceEditor: NSViewControllerRepresentable {
         if controller.language.id != language.id {
             controller.language = language
         }
+
         if controller.theme != theme {
             controller.theme = theme
         }
+
         if controller.indentOption != indentOption {
             controller.indentOption = indentOption
         }
+
         if controller.tabWidth != tabWidth {
             controller.tabWidth = tabWidth
         }
+
         if controller.letterSpacing != letterSpacing {
             controller.letterSpacing = letterSpacing
         }

Sources/CodeEditSourceEditor/Highlighting/Highlighter.swift

@@ -36,10 +36,6 @@ class Highlighter: NSObject {
         return IndexSet(integersIn: textView?.visibleTextRange ?? NSRange())
     }()
 
-    // MARK: - Tasks
-
-    private var runningTasks: [UUID: Task<Void, Never>] = [:]
-
     // MARK: - UI
 
     /// The text view to highlight
@@ -114,6 +110,15 @@ class Highlighter: NSObject {
     /// - Parameter language: The language to update to.
     public func setLanguage(language: CodeLanguage) {
         guard let textView = self.textView else { return }
+        // Remove all current highlights. Makes the language setting feel snappier and tells the user we're doing
+        // something immediately.
+        textView.textStorage.setAttributes(
+            attributeProvider.attributesFor(nil),
+            range: NSRange(location: 0, length: textView.textStorage.length)
+        )
+        textView.layoutManager.invalidateLayoutForRect(textView.visibleRect)
+        validSet.removeAll()
+        pendingSet.removeAll()
         highlightProvider?.setUp(textView: textView, codeLanguage: language)
         invalidate()
     }
@@ -304,11 +309,11 @@ extension Highlighter {
             visibleSet.insert(range: editedRange)
         }
 
+        updateVisibleSet(textView: textView)
+
         highlightProvider?.applyEdit(textView: textView, range: range, delta: delta) { [weak self] invalidIndexSet in
             let indexSet = invalidIndexSet
                 .union(IndexSet(integersIn: editedRange))
-                // Only invalidate indices that are visible.
-                .intersection(self?.visibleSet ?? IndexSet())
 
             for range in indexSet.rangeView {
                 self?.invalidate(range: NSRange(range))

Sources/CodeEditSourceEditor/TreeSitter/TreeSitterClient.swift

@@ -218,7 +218,7 @@ public final class TreeSitterClient: HighlightProviding {
             let longDocument = textView.documentRange.length > Constants.maxSyncContentLength
 
             if longEdit || longDocument {
-
+                throw Error.syncUnavailable
             }
             try performSync(operation)
         } catch {