Fix Cmd+A highlight missing last line on trailing-newline documents

Sources/CodeEditTextView/TextLineStorage/TextLineStorage+Iterator.swift

@@ -72,8 +72,16 @@ public extension TextLineStorage {
 
         public mutating func next() -> TextLinePosition? {
             if let currentPosition {
-                guard currentPosition.range.max < range.max,
-                      let nextPosition = storage.getLine(atIndex: currentPosition.index + 1) else {
+                guard let nextPosition = storage.getLine(atIndex: currentPosition.index + 1) else {
+                    return nil
+                }
+                // An empty trailing line (length 0) sits at the same offset as the previous
+                // line's `range.max`. Without this exception, iterating to the end of the
+                // document would skip it — see issue #121 (Cmd+A highlight missing the last
+                // empty line on documents ending with a newline).
+                let isTrailingEmptyLineAtRangeEnd = nextPosition.range.length == 0
+                    && nextPosition.range.location == range.max
+                guard currentPosition.range.max < range.max || isTrailingEmptyLineAtRangeEnd else {
                     return nil
                 }
                 self.currentPosition = nextPosition

Tests/CodeEditTextViewTests/LayoutManager/TextLayoutManagerTests.swift

@@ -181,6 +181,23 @@ struct TextLayoutManagerTests {
         }
     }
 
+    /// Documents that end with a line ending get an empty trailing line in storage. Iterating the
+    /// document range must include it, otherwise `Cmd+A` selects the line but never highlights it.
+    /// Regression test for https://github.com/CodeEditApp/CodeEditTextView/issues/121.
+    @Test
+    func rangeIteratorIncludesTrailingEmptyLine() {
+        textStorage.mutableString.setString("a\nb\nc\n")
+        layoutManager.layoutLines(in: NSRect(x: 0, y: 0, width: 1000, height: 1000))
+
+        let docRange = NSRange(location: 0, length: textStorage.length)
+        let iterated = Array(layoutManager.lineStorage.linesInRange(docRange))
+
+        #expect(layoutManager.lineStorage.count == 4, "Storage should hold 3 lines + 1 trailing empty line")
+        #expect(iterated.count == layoutManager.lineStorage.count, "Trailing empty line was skipped")
+        #expect(iterated.last?.range.length == 0)
+        #expect(iterated.last?.range.location == textStorage.length)
+    }
+
     @Test
     func afterLayoutDoesntNeedLayout() {
         layoutManager.layoutLines(in: NSRect(x: 0, y: 0, width: 1000, height: 1000))