term: implement EraseInDisplay::EraseScrollback

refs: https://github.com/wez/wezterm/issues/194

term/src/screen.rs

@@ -469,6 +469,15 @@ impl Screen {
         }
     }
 
+    pub fn erase_scrollback(&mut self) {
+        let len = self.lines.len();
+        let to_clear = len - self.physical_rows;
+        for _ in 0..to_clear {
+            self.lines.pop_front();
+            self.stable_row_index_offset += 1;
+        }
+    }
+
     /// ---------
     /// |
     /// |--- top

term/src/terminalstate.rs

@@ -1333,7 +1333,7 @@ impl TerminalState {
             }
             EraseInDisplay::EraseDisplay => 0..rows,
             EraseInDisplay::EraseScrollback => {
-                error!("TODO: ed: no support for xterm Erase Saved Lines yet");
+                self.screen_mut().erase_scrollback();
                 return;
             }
         };

term/src/test/csi.rs

@@ -183,3 +183,12 @@ fn test_ed() {
         Compare::TEXT | Compare::ATTRS,
     );
 }
+
+#[test]
+fn test_ed_erase_scrollback() {
+    let mut term = TestTerm::new(3, 3, 3);
+    term.print("abc\r\ndef\r\nghi\r\n111\r\n222\r\na\x1b[3J");
+    assert_all_contents(&term, file!(), line!(), &["111", "222", "a  "]);
+    term.print("b");
+    assert_all_contents(&term, file!(), line!(), &["111", "222", "ab "]);
+}