fix: delete trailing ASCII when accepting prediction

Author: ensan-hcl

Core/Sources/Core/InputUtils/SegmentsManager.swift

@@ -820,16 +820,6 @@ public final class SegmentsManager {
             return []
         }
 
-        var matchTarget = target
-        if let last = matchTarget.last,
-           last.unicodeScalars.allSatisfy({ $0.isASCII && CharacterSet.letters.contains($0) }) {
-            matchTarget.removeLast()
-        }
-        guard matchTarget.count >= 2 else {
-            return []
-        }
-        matchTarget = matchTarget.toHiragana()
-
         if let backspaceAdjustedPredictionCandidate {
             return [backspaceAdjustedPredictionCandidate]
         }
@@ -843,23 +833,51 @@ public final class SegmentsManager {
             guard !reading.isEmpty else {
                 continue
             }
-            let readingHiragana = reading.toHiragana()
-            guard readingHiragana.hasPrefix(matchTarget) else {
-                continue
+            if let predictionCandidate = Self.makePredictionCandidate(
+                currentTarget: target,
+                candidateReading: reading,
+                displayText: candidate.text
+            ) {
+                return [predictionCandidate]
             }
-            guard matchTarget.count < readingHiragana.count else {
-                continue
-            }
-            let appendText = String(readingHiragana.dropFirst(matchTarget.count))
-            guard !appendText.isEmpty else {
-                continue
-            }
-            return [.init(displayText: candidate.text, appendText: appendText)]
         }
 
         return []
     }
 
+    static func makePredictionCandidate(
+        currentTarget: String,
+        candidateReading: String,
+        displayText: String
+    ) -> PredictionCandidate? {
+        var matchTarget = currentTarget
+        var deleteCount = 0
+        if let last = matchTarget.last,
+           last.unicodeScalars.allSatisfy({ $0.isASCII && CharacterSet.letters.contains($0) }) {
+            matchTarget.removeLast()
+            deleteCount = 1
+        }
+        guard matchTarget.count >= 2 else {
+            return nil
+        }
+
+        let readingHiragana = candidateReading.toHiragana()
+        let matchTargetHiragana = matchTarget.toHiragana()
+        guard readingHiragana.hasPrefix(matchTargetHiragana) else {
+            return nil
+        }
+        guard matchTargetHiragana.count < readingHiragana.count else {
+            return nil
+        }
+
+        let appendText = String(readingHiragana.dropFirst(matchTargetHiragana.count))
+        guard !appendText.isEmpty else {
+            return nil
+        }
+
+        return .init(displayText: displayText, appendText: appendText, deleteCount: deleteCount)
+    }
+
     private func requestTypoCorrectionCandidates(composingText targetComposingText: ComposingText, inputStyle: InputStyle) -> [String] {
         guard Config.DebugTypoCorrection().value && self.hasDebugTypoCorrectionWeights() else {
             return []

Core/Tests/CoreTests/InputUtilsTests/SegmentsManagerPredictionCandidateTests.swift

@@ -0,0 +1,26 @@
+@testable import Core
+import Testing
+
+@Test func testMakePredictionCandidateDeletesTrailingASCIIUsedForMatching() async throws {
+    let candidate = SegmentsManager.makePredictionCandidate(
+        currentTarget: "おはようございm",
+        candidateReading: "おはようございます",
+        displayText: "おはようございます"
+    )
+
+    #expect(candidate?.displayText == "おはようございます")
+    #expect(candidate?.appendText == "ます")
+    #expect(candidate?.deleteCount == 1)
+}
+
+@Test func testMakePredictionCandidateKeepsDeleteCountZeroWithoutTrailingASCII() async throws {
+    let candidate = SegmentsManager.makePredictionCandidate(
+        currentTarget: "おはようござい",
+        candidateReading: "おはようございます",
+        displayText: "おはようございます"
+    )
+
+    #expect(candidate?.displayText == "おはようございます")
+    #expect(candidate?.appendText == "ます")
+    #expect(candidate?.deleteCount == 0)
+}