run down an off-by-one in VPA handling

This manifested with vim-inside-tmux losing my top tmux status line.

Add a test!

term/src/csi.rs

@@ -486,7 +486,7 @@ impl<'a> Iterator for CSIParser<'a> {
 
             // VPA: Line Position Absolute
             ('d', &[], Some(&[])) => Some(CSIAction::LinePosition(Position::Absolute(0))),
-            ('d', &[], Some(&[n])) => Some(CSIAction::LinePosition(Position::Absolute(n))),
+            ('d', &[], Some(&[n])) => Some(CSIAction::LinePosition(Position::Absolute(n - 1))),
 
             // VPR: Line Position Relative
             ('e', &[], Some(&[])) => Some(CSIAction::LinePosition(Position::Relative(0))),

term/src/screen.rs

@@ -97,11 +97,11 @@ impl Screen {
     ) -> &Cell {
         let line_idx = self.phys_row(y);
         debug!(
-            "set_cell x,y {},{}, line_idx = {} {} {:?}",
+            "set_cell {} x={} y={} phys={} {:?}",
+            c,
             x,
             y,
             line_idx,
-            c,
             attr
         );
 
@@ -177,6 +177,7 @@ impl Screen {
     /// If the top of the region is the top of the visible display, rather than
     /// removing the lines we let them go into the scrollback.
     pub fn scroll_up(&mut self, scroll_region: &Range<VisibleRowIndex>, num_rows: usize) {
+        debug!("scroll_up {:?} {}", scroll_region, num_rows);
         let phys_scroll = self.phys_range(&scroll_region);
         assert!(num_rows <= phys_scroll.end - phys_scroll.start);
 
@@ -233,6 +234,7 @@ impl Screen {
     /// In other words, we remove (bottom-num_rows..bottom) and then insert num_rows
     /// at scroll_top.
     pub fn scroll_down(&mut self, scroll_region: &Range<VisibleRowIndex>, num_rows: usize) {
+        debug!("scroll_down {:?} {}", scroll_region, num_rows);
         let phys_scroll = self.phys_range(&scroll_region);
         assert!(num_rows <= phys_scroll.end - phys_scroll.start);
 

term/src/terminalstate.rs

@@ -1147,10 +1147,12 @@ impl vte::Perform for TerminalState {
             (b'\\', &[], &[]) => {}
             // Application Keypad (DECKPAM)
             (b'=', &[], &[]) => {
+                debug!("DECKPAM on");
                 self.application_keypad = true;
             }
             // Normal Keypad (DECKPAM)
             (b'>', &[], &[]) => {
+                debug!("DECKPAM off");
                 self.application_keypad = false;
             }
             // Reverse Index (RI)
@@ -1163,9 +1165,13 @@ impl vte::Perform for TerminalState {
             (b'H', &[], &[]) => self.c1_hts(),
 
             // Enable alternate character set mode (smacs)
-            (b'0', &[b'('], &[]) => {}
+            (b'0', &[b'('], &[]) => {
+                debug!("ESC: smacs");
+            }
             // Exit alternate character set mode (rmacs)
-            (b'B', &[b'('], &[]) => {}
+            (b'B', &[b'('], &[]) => {
+                debug!("ESC: rmacs");
+            }
 
             // DECSC - Save Cursor
             (b'7', &[], &[]) => self.perform_csi(CSIAction::SaveCursor),

term/src/test/csi.rs

@@ -0,0 +1,18 @@
+use super::*;
+
+#[test]
+fn test_vpa() {
+    let mut term = TestTerm::new(3, 4, 0);
+    term.assert_cursor_pos(0, 0, None);
+    term.print("a\nb\nc");
+    term.assert_cursor_pos(1, 2, None);
+    term.print("\x1b[d");
+    term.assert_cursor_pos(1, 0, None);
+    term.print("\n\n");
+    term.assert_cursor_pos(0, 2, None);
+
+    // escapes are 1-based, so check that we're handling that
+    // when we parse them!
+    term.print("\x1b[2d");
+    term.assert_cursor_pos(0, 1, None);
+}

term/src/test/mod.rs

@@ -5,6 +5,7 @@ use super::*;
 mod selection;
 mod c0;
 mod c1;
+mod csi;
 
 #[derive(Default, Debug)]
 struct TestHost {