[Link] Fix OneTimeTextField crash in Mac Catalyst (#1416)

* Fix OneTimeTextField crash in Mac Catalyst

* Update README

* Fix rect calculation

* Cleanup

* Fix and document implementation

CHANGELOG.md

@@ -1,3 +1,7 @@
+## X.Y.Z
+### PaymentSheet
+* [Fixed] Fixed potential crash when using Link in Mac Catalyst.
+
 ## 22.8.0 2022-09-06
 ### PaymentSheet
 * [Changed] Renamed `PaymentSheet.reset()` to `PaymentSheet.resetCustomer()`. See `MIGRATING.md` for more info.

Stripe/OneTimeCodeTextField.swift

@@ -360,6 +360,16 @@ extension OneTimeCodeTextField: UIKeyInput {
 
 }
 
+// MARK: - Utils
+
+extension OneTimeCodeTextField {
+
+    private func clampIndex(_ index: Int) -> Int {
+        return max(min(index, numberOfDigits - 1), 0)
+    }
+
+}
+
 // MARK: - UITextInput
 
 extension OneTimeCodeTextField: UITextInput {
@@ -517,15 +527,25 @@ extension OneTimeCodeTextField: UITextInput {
     }
 
     func firstRect(for range: UITextRange) -> CGRect {
-        guard let range = range as? TextRange else {
+        guard let range = range as? TextRange, !range.isEmpty else {
             return .zero
         }
 
-        let firstDigitView = digitViews[range._start.index]
-        let secondDigitView = digitViews[range._end.index]
+        // This method should return a rectangle that contains the digit views that
+        // fall inside the given TextRange. For example, a [0,2] TextRange should
+        // return a rectangle that contains digit views 0 and 1:
+        //
+        // 0   1   2    3    4   5   6  <- TextPosition
+        //  [*] [*] [*]   [*] [*] [*]   <- UI
+        //   0   1   2     3   4   5    <- DigitView index
+        // ^       ^
+        // |_______|                    <- [0,2] TextRange
+
+        let firstDigitView = digitViews[clampIndex(range._start.index)]
+        let secondDigitView = digitViews[clampIndex(range._end.index - 1)]
 
         let firstRect = firstDigitView.convert(firstDigitView.bounds, to: self)
-        let secondRect = firstDigitView.convert(secondDigitView.bounds, to: self)
+        let secondRect = secondDigitView.convert(secondDigitView.bounds, to: self)
 
         return firstRect.union(secondRect)
     }
@@ -535,7 +555,7 @@ extension OneTimeCodeTextField: UITextInput {
             return .zero
         }
 
-        let digitView = digitViews[position.index]
+        let digitView = digitViews[clampIndex(position.index)]
         return digitView.convert(digitView.caretRect, to: self)
     }
 

Tests/Tests/OneTimeCodeTextFieldTests.swift

@@ -236,6 +236,36 @@ class OneTimeCodeTextFieldTests: XCTestCase {
         XCTAssertNil(field.characterRange(byExtending: position, in: .down))
     }
 
+    func test_firstRectForRange_singleDigit() {
+        let sut = makeSUT(value: "123456")
+
+        // A [0,1] text range
+        let range = OneTimeCodeTextField.TextRange(
+            start: OneTimeCodeTextField.TextPosition(0),
+            end: OneTimeCodeTextField.TextPosition(1)
+        )
+        let rect = sut.firstRect(for: range)
+        XCTAssertEqual(rect.minX, 0, accuracy: 0.2)
+        XCTAssertEqual(rect.minY, 0, accuracy: 0.2)
+        XCTAssertEqual(rect.width, 46.0, accuracy: 0.2)
+        XCTAssertEqual(rect.height, 60, accuracy: 0.2)
+    }
+
+    func test_firstRectForRange_multipleDigits() {
+        let sut = makeSUT(value: "123456")
+
+        // A [0,3] Text range
+        let range = OneTimeCodeTextField.TextRange(
+            start: OneTimeCodeTextField.TextPosition(0),
+            end: OneTimeCodeTextField.TextPosition(3)
+        )
+        let rect = sut.firstRect(for: range)
+        XCTAssertEqual(rect.minX, 0, accuracy: 0.2)
+        XCTAssertEqual(rect.minY, 0, accuracy: 0.2)
+        XCTAssertEqual(rect.width, 150, accuracy: 0.2)
+        XCTAssertEqual(rect.height, 60, accuracy: 0.2)
+    }
+
     func test_caretRectForPosition() {
         let sut = makeSUT()
         let frame = sut.caretRect(for: OneTimeCodeTextField.TextPosition(1))