command/hook_ui: Truncate the ID considering multibyte characters

Fixes #18822

The `tuncatedId` function had been introduced in #12261 and increased the
`maxIdLen` to 80 in #13317. Since the number of bytes itself seems to be
unimportant, the ID should be truncated to 80 characters, not 80 bytes.

command/hook_ui.go

@@ -373,7 +373,10 @@ func dropCR(data []byte) []byte {
 }
 
 func truncateId(id string, maxLen int) string {
-	totalLength := len(id)
+	// Note that the id may contain multibyte characters.
+	// We need to truncate it to maxLen characters, not maxLen bytes.
+	rid := []rune(id)
+	totalLength := len(rid)
 	if totalLength <= maxLen {
 		return id
 	}
@@ -383,11 +386,11 @@ func truncateId(id string, maxLen int) string {
 		maxLen = 5
 	}
 
-	dots := "..."
+	dots := []rune("...")
 	partLen := maxLen / 2
 
 	leftIdx := partLen - 1
-	leftPart := id[0:leftIdx]
+	leftPart := rid[0:leftIdx]
 
 	rightIdx := totalLength - partLen - 1
 
@@ -396,7 +399,7 @@ func truncateId(id string, maxLen int) string {
 		rightIdx -= overlap
 	}
 
-	rightPart := id[rightIdx:]
+	rightPart := rid[rightIdx:]
 
-	return leftPart + dots + rightPart
+	return string(leftPart) + string(dots) + string(rightPart)
 }

command/hook_ui_test.go

@@ -252,6 +252,51 @@ func TestTruncateId(t *testing.T) {
 			Expected: "Hello world",
 			MaxLen:   12,
 		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あ...さ",
+			MaxLen:   3,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あ...さ",
+			MaxLen:   5,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あい...さ",
+			MaxLen:   6,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あい...こさ",
+			MaxLen:   7,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あいう...こさ",
+			MaxLen:   8,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あいう...けこさ",
+			MaxLen:   9,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あいうえ...けこさ",
+			MaxLen:   10,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あいうえおかきくけこさ",
+			MaxLen:   11,
+		},
+		{
+			Input:    "あいうえおかきくけこさ",
+			Expected: "あいうえおかきくけこさ",
+			MaxLen:   12,
+		},
 	}
 	for i, tc := range testCases {
 		testName := fmt.Sprintf("%d", i)