CtlCandidateTDK // Add isFilterable().

Packages/vChewing_CandidateWindow/Sources/CandidateWindow/CandidatePool.swift

@@ -232,6 +232,16 @@ public extension CandidatePool {
     }
     return (min, nil)
   }
+
+  func isFilterable(target index: Int) -> Bool {
+    let spanLength = candidateDataAll[index].spanLength
+    guard spanLength == 1 else { return true }
+    return cellsOf(spanLength: spanLength).count > 1
+  }
+
+  func cellsOf(spanLength: Int) -> [CandidateCellData] {
+    candidateDataAll.filter { $0.spanLength == spanLength }
+  }
 }
 
 // MARK: - Privates.

Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/VwrCandidateTDK_Cocoa.swift

@@ -333,6 +333,7 @@ private extension VwrCandidateTDKCocoa {
     var theMenu: NSMenu?
 
     private func prepareMenu() {
+      guard let thePool = (target as? VwrCandidateTDKCocoa)?.thePool else { return }
       let newMenu = NSMenu()
       let boostMenuItem = NSMenuItem(
         title: "↑ \(cellData.displayedText)",
@@ -350,9 +351,7 @@ private extension VwrCandidateTDKCocoa {
       nerfMenuItem.target = self
       newMenu.addItem(nerfMenuItem)
 
-      if let dataAll = (target as? VwrCandidateTDKCocoa)?.thePool.candidateDataAll,
+      if thePool.isFilterable(target: cellData.index) {
-         dataAll.count > cellData.index, dataAll[cellData.index].spanLength > 1
-      {
         let filterMenuItem = NSMenuItem(
           title: "✖︎ \(cellData.displayedText)",
           action: #selector(menuActionOfFiltering(_:)),

Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/VwrCandidateTDK_SwiftUI.swift

@@ -168,9 +168,7 @@ extension VwrCandidateTDK {
           } label: {
             Text("↓ " + cell.displayedText)
           }
-          if thePool.candidateDataAll.count > cell.index,
+          if thePool.isFilterable(target: cell.index) {
-             thePool.candidateDataAll[cell.index].spanLength > 1
-          {
             Button {
               didRightClickCandidateAt(cell.index, action: .toFilter)
             } label: {