replaceString was crashing on acceptable input

Author: mattmassicotte

TextViewPlus/NSTextView+AttributedString.swift

@@ -20,17 +20,31 @@ public extension NSTextView {
         didChangeText()
     }
 
+    // swiftlint:disable line_length
+    private func safeAttributedSubstring(forProposedRange range: NSRange, actualRange: NSRangePointer?) -> NSAttributedString? {
+        // attributedSubstring returns nil for out-of-range AND for length == 0. But, zero-length ranges
+        // are totally acceptable, and I'm not sure that's reasonable behavior.
+        let maxLength = textStorage?.length ?? 0
+
+        guard NSMaxRange(range) <= maxLength else {
+            fatalError("Range out of bounds for underlying storage")
+        }
+
+        // also, we must have a copy, as the underlying TextStorage can change, and it seems the
+        // string is changing along with it.
+        return attributedSubstring(forProposedRange: range, actualRange: actualRange)?.copy() as? NSAttributedString
+    }
+
     func replaceString(in range: NSRange, with attributedString: NSAttributedString) {
         if let manager = undoManager {
-            guard let originalString = attributedSubstring(forProposedRange: range, actualRange: nil) else {
-                fatalError("Range invalid for string")
-            }
+            let originalString = safeAttributedSubstring(forProposedRange: range, actualRange: nil)
+            let usableReplacementString = originalString ?? NSAttributedString()
 
             let inverseLength = attributedString.length
             let inverseRange = NSRange(location: range.location, length: inverseLength)
 
             manager.registerUndo(withTarget: self, handler: { (view) in
-                view.replaceString(in: inverseRange, with: originalString)
+                view.replaceString(in: inverseRange, with: usableReplacementString)
             })
         }
 

TextViewPlus/TextViewPlus.xcconfig

@@ -12,8 +12,8 @@
 PRODUCT_NAME = TextViewPlus
 PRODUCT_BUNDLE_IDENTIFIER = com.chimehq.TextViewPlus
 PRODUCT_MODULE_NAME = TextViewPlus
-CURRENT_PROJECT_VERSION = 2
-MARKETING_VERSION = 1.0
+CURRENT_PROJECT_VERSION = 3
+MARKETING_VERSION = 1.0.1
 
 INFOPLIST_FILE = TextViewPlus/Info.plist
 FRAMEWORK_SEARCH_PATHS = $(PROJECT_DIR)/Carthage/Build/Mac $(PROJECT_DIR)/Carthage/Build/Mac/Static

TextViewPlusTests/TextViewPlusTests.swift

@@ -22,4 +22,30 @@ class TextViewPlusTests: XCTestCase {
 
         XCTAssertEqual(textView.string, "abc")
     }
+
+    func testProgrammaticModificationOfAttributedStringWithZeroLengthRange() {
+        let textView = TestableTextView(string: "abc")
+
+        let attrString = NSAttributedString(string: "z")
+        textView.replaceString(in: NSRange(location: 1, length: 0), with: attrString)
+
+        XCTAssertEqual(textView.string, "azbc")
+
+        textView.undoManager!.undo()
+
+        XCTAssertEqual(textView.string, "abc")
+    }
+
+    func testProgrammaticModificationOfAttributedStringWithFullRange() {
+        let textView = TestableTextView(string: "abc")
+
+        let attrString = NSAttributedString(string: "def")
+        textView.replaceString(in: NSRange(location: 0, length: 3), with: attrString)
+
+        XCTAssertEqual(textView.string, "def")
+
+        textView.undoManager!.undo()
+
+        XCTAssertEqual(textView.string, "abc")
+    }
 }