Add Emacs-style mark commands (setMark:, selectToMark:, swapWithMark:, deleteToMark:)

Sources/STTextViewAppKit/STTextView+Mark.swift

@@ -0,0 +1,49 @@
+//  Created by Marcin Krzyzanowski
+//  https://github.com/krzyzanowskim/STTextView/blob/main/LICENSE.md
+
+import AppKit
+
+extension STTextView {
+
+    /// The mark is a saved selection that later commands can select to, swap with, or kill to.
+    /// Together with `yank(_:)` it completes the Emacs-style command family from
+    /// `NSStandardKeyBindingResponding`, which multi-step `DefaultKeyBinding.dict`
+    /// macros (line moves, paragraph cut/copy, …) are commonly built on.
+    ///
+    /// https://www.gnu.org/software/emacs/manual/html_node/emacs/Setting-Mark.html
+    override open func setMark(_ sender: Any?) {
+        _mark = textSelection
+    }
+
+    /// Exchanges the current selection with the mark, so the two locations can be toggled between.
+    override open func swapWithMark(_ sender: Any?) {
+        guard let mark = clampedMark() else { return }
+        _mark = textSelection
+        textSelection = mark
+    }
+
+    /// Extends the selection to cover everything between the mark and the current selection.
+    override open func selectToMark(_ sender: Any?) {
+        guard let mark = clampedMark() else { return }
+        textSelection = NSUnionRange(mark, textSelection)
+    }
+
+    /// Deletes everything between the mark and the current selection, adding it to the kill ring
+    /// (routed through `deleteBackward(_:)`, which feeds `_yankingManager`) so a following
+    /// `yank(_:)` reinserts it.
+    override open func deleteToMark(_ sender: Any?) {
+        guard let mark = clampedMark() else { return }
+        textSelection = NSUnionRange(mark, textSelection)
+        deleteBackward(sender)
+        _mark = textSelection
+    }
+
+    /// The mark survives arbitrary edits, so by the time it's used it can point past the current
+    /// text end (or into it with excess length).
+    private func clampedMark() -> NSRange? {
+        guard let mark = _mark else { return nil }
+        let length = textContentManager.length
+        let location = min(mark.location, length)
+        return NSRange(location: location, length: min(mark.length, length - location))
+    }
+}

Sources/STTextViewAppKit/STTextView.swift

@@ -421,6 +421,10 @@ open class STTextView: NSView, NSTextInput, NSTextContent, STTextViewProtocol {
     var _undoManager: UndoManager?
     var _yankingManager = YankingManager()
 
+    /// The Emacs-style mark set by `setMark(_:)` and consumed by
+    /// `selectToMark(_:)`, `swapWithMark(_:)` and `deleteToMark(_:)`.
+    var _mark: NSRange?
+
     var markedText: STMarkedText?
 
     /// The attributes used to draw marked text.

Tests/STTextViewAppKitTests/MarkTests.swift

@@ -0,0 +1,78 @@
+#if os(macOS)
+    import XCTest
+    @testable import STTextViewAppKit
+
+    class MarkTests: XCTestCase {
+
+        func testSwapWithMark() {
+            let textView = STTextView()
+            textView.text = "abc def"
+
+            textView.textSelection = NSRange(location: 0, length: 3)
+            textView.setMark(nil)
+            textView.textSelection = NSRange(location: 4, length: 3)
+
+            textView.swapWithMark(nil)
+            XCTAssertEqual(textView.textSelection, NSRange(location: 0, length: 3))
+
+            textView.swapWithMark(nil)
+            XCTAssertEqual(textView.textSelection, NSRange(location: 4, length: 3))
+        }
+
+        func testSelectToMark() {
+            let textView = STTextView()
+            textView.text = "abc def ghi"
+
+            textView.textSelection = NSRange(location: 0, length: 3)
+            textView.setMark(nil)
+            textView.textSelection = NSRange(location: 8, length: 0)
+
+            textView.selectToMark(nil)
+            XCTAssertEqual(textView.textSelection, NSRange(location: 0, length: 8))
+        }
+
+        func testDeleteToMarkFeedsKillRing() {
+            let textView = STTextView()
+            textView.text = "abc def ghi"
+
+            textView.textSelection = NSRange(location: 4, length: 0)
+            textView.setMark(nil)
+            textView.textSelection = NSRange(location: 8, length: 0)
+
+            textView.deleteToMark(nil)
+            XCTAssertEqual(textView.text, "abc ghi")
+
+            textView.textSelection = NSRange(location: 0, length: 0)
+            textView.yank(nil)
+            XCTAssertEqual(textView.text, "def abc ghi")
+        }
+
+        func testStaleMarkIsClampedAfterEdits() {
+            let textView = STTextView()
+            textView.text = "abcdefgh"
+
+            textView.textSelection = NSRange(location: 8, length: 0)
+            textView.setMark(nil)
+            textView.text = "abc"
+            textView.textSelection = NSRange(location: 0, length: 0)
+
+            textView.selectToMark(nil)
+            XCTAssertEqual(textView.textSelection, NSRange(location: 0, length: 3))
+        }
+
+        func testCommandsWithoutMarkAreNoOps() {
+            let textView = STTextView()
+            textView.text = "abc"
+            textView.textSelection = NSRange(location: 1, length: 0)
+
+            textView.swapWithMark(nil)
+            textView.selectToMark(nil)
+            textView.deleteToMark(nil)
+
+            XCTAssertEqual(textView.text, "abc")
+            XCTAssertEqual(textView.textSelection, NSRange(location: 1, length: 0))
+        }
+
+    }
+
+#endif