implement TextArea::select_all

but it is not assigned to default key shortcuts because C-a is already
in use.

README.md

@@ -489,6 +489,7 @@ notify how to move the cursor.
 | `textarea.paste()`                                   | Paste yanked text                               |
 | `textarea.start_selection()`                         | Start text selection                            |
 | `textarea.cancel_selection()`                        | Cancel text selection                           |
+| `textarea.select_all()`                              | Select entire text                              |
 | `textarea.move_cursor(CursorMove::Forward)`          | Move cursor forward by one character            |
 | `textarea.move_cursor(CursorMove::Back)`             | Move cursor backward by one character           |
 | `textarea.move_cursor(CursorMove::Up)`               | Move cursor up by one line                      |

src/textarea.rs

@@ -1312,6 +1312,26 @@ impl<'a> TextArea<'a> {
         self.selection_start = None;
     }
 
+    /// Select the entire text. Cursor moves to the end of the text buffer. When text selection is already ongoing,
+    /// it is canceled.
+    /// ```
+    /// use tui_textarea::{TextArea, CursorMove};
+    ///
+    /// let mut textarea = TextArea::from(["aaa", "bbb", "ccc"]);
+    ///
+    /// textarea.select_all();
+    ///
+    /// // Cut the entire text;
+    /// textarea.cut();
+    ///
+    /// assert_eq!(textarea.lines(), [""]); // Buffer is now empty
+    /// assert_eq!(textarea.yank_text(), "aaa\nbbb\nccc");
+    /// ```
+    pub fn select_all(&mut self) {
+        self.move_cursor(CursorMove::Jump(u16::MAX, u16::MAX));
+        self.selection_start = Some((0, 0));
+    }
+
     /// Return if text selection is ongoing or not.
     /// ```
     /// use tui_textarea::{TextArea};

tests/textarea.rs

@@ -1420,6 +1420,18 @@ fn test_set_yank_paste_text() {
     }
 }
 
+#[test]
+fn test_select_all() {
+    let mut t = TextArea::from(["aaa", "bbb", "ccc"]);
+    t.select_all();
+    assert!(t.is_selecting());
+    assert_eq!(t.cursor(), (2, 3));
+    t.cut();
+    assert_eq!(t.lines(), [""]);
+    assert_eq!(t.yank_text(), "aaa\nbbb\nccc");
+    assert_undo_redo((2, 3), &["aaa", "bbb", "ccc"], &[""], &mut t, "");
+}
+
 struct DeleteTester(&'static [&'static str], fn(&mut TextArea) -> bool);
 impl DeleteTester {
     fn test(&self, before: (usize, usize), after: (usize, usize, &[&str], &str)) {