Gracefully avoid linebreak within short candidates

sources/SquirrelPanel.swift

@@ -223,7 +223,11 @@ final class SquirrelPanel: NSPanel {
 
       let line = NSMutableAttributedString(string: theme.candidateFormat, attributes: labelAttrs)
       for range in line.string.ranges(of: /\[candidate\]/) {
-        line.addAttributes(attrs, range: convert(range: range, in: line.string))
+        let convertedRange = convert(range: range, in: line.string)
+        line.addAttributes(attrs, range: convertedRange)
+        if candidate.count <= 5 {
+          line.addAttribute(.noBreak, value: true, range: NSMakeRange(convertedRange.location+1, convertedRange.length-1))
+        }
       }
       for range in line.string.ranges(of: /\[comment\]/) {
         line.addAttributes(commentAttrs, range: convert(range: range, in: line.string))
@@ -233,6 +237,10 @@ final class SquirrelPanel: NSPanel {
       line.mutableString.replaceOccurrences(of: "[candidate]", with: candidate, range: NSMakeRange(0, line.length))
       line.mutableString.replaceOccurrences(of: "[comment]", with: comment, range: NSMakeRange(0, line.length))
 
+      if line.length <= 10 {
+        line.addAttribute(.noBreak, value: true, range: NSMakeRange(1, line.length-1))
+      }
+
       let lineSeparator = NSAttributedString(string: linear ? "  " : "\n", attributes: attrs)
       if i > 0 {
         text.append(lineSeparator)

sources/SquirrelView.swift

@@ -10,6 +10,7 @@ import AppKit
 final class SquirrelView: NSView {
   let textView: NSTextView
 
+  private let squirrelLayoutDelegate: SquirrelLayoutDelegate
   var candidateRanges: [NSRange] = []
   var hilightedIndex = 0
   var preeditRange = NSMakeRange(NSNotFound, 0)
@@ -33,10 +34,12 @@ final class SquirrelView: NSView {
   }
 
   override init(frame frameRect: NSRect) {
+    squirrelLayoutDelegate = SquirrelLayoutDelegate()
     textView = NSTextView(frame: frameRect)
     textView.drawsBackground = false
     textView.isEditable = false
     textView.isSelectable = false
+    textView.textLayoutManager?.delegate = squirrelLayoutDelegate
     super.init(frame: frameRect)
     textContainer.lineFragmentPadding = 0
     self.wantsLayer = true
@@ -57,7 +60,7 @@ final class SquirrelView: NSView {
     guard range.location != NSNotFound else { return nil }
     guard let startLocation = textLayoutManager.location(textLayoutManager.documentRange.location, offsetBy: range.location) else { return nil }
     guard let endLocation = textLayoutManager.location(startLocation, offsetBy: range.length) else { return nil }
-    return NSTextRange(location: startLocation, end: endLocation) ?? textLayoutManager.documentRange
+    return NSTextRange(location: startLocation, end: endLocation)
   }
 
   // Get the rectangle containing entire contents, expensive to calculate
@@ -679,3 +682,17 @@ private extension SquirrelView {
     return newRect
   }
 }
+
+fileprivate class SquirrelLayoutDelegate: NSObject, NSTextLayoutManagerDelegate {
+  func textLayoutManager(_ textLayoutManager: NSTextLayoutManager, shouldBreakLineBefore location: any NSTextLocation, hyphenating: Bool) -> Bool {
+    let index = textLayoutManager.offset(from: textLayoutManager.documentRange.location, to: location)
+    if let attributes = textLayoutManager.textContainer?.textView?.textContentStorage?.attributedString?.attributes(at: index, effectiveRange: nil), let noBreak = attributes[.noBreak] as? Bool, noBreak {
+      return false
+    }
+    return true
+  }
+}
+
+extension NSAttributedString.Key {
+  static let noBreak = NSAttributedString.Key("noBreak")
+}