terminal: cursor back handles reverse wrap (mode 45)

src/terminal/Screen.zig

@@ -350,6 +350,10 @@ pub const Row = struct {
         return self.storage[0].header.flags.dirty;
     }
 
+    pub inline fn isWrapped(self: Row) bool {
+        return self.storage[0].header.flags.wrap;
+    }
+
     /// Set the semantic prompt state for this row.
     pub fn setSemanticPrompt(self: Row, p: RowHeader.SemanticPrompt) void {
         self.storage[0].header.flags.semantic_prompt = p;

src/terminal/Terminal.zig

@@ -1358,6 +1358,15 @@ pub fn cursorLeft(self: *Terminal, count_req: usize) void {
     const tracy = trace(@src());
     defer tracy.end();
 
+    // Wrapping behavior depends on various terminal modes
+    const WrapMode = enum { none, reverse, reverse_extended };
+    const wrap_mode: WrapMode = wrap_mode: {
+        if (!self.modes.get(.wraparound)) break :wrap_mode .none;
+        if (self.modes.get(.reverse_wrap)) break :wrap_mode .reverse;
+        if (self.modes.get(.reverse_wrap_extended)) break :wrap_mode .reverse_extended;
+        break :wrap_mode .none;
+    };
+
     // If we have a pending wrap state on, we reset it and reduce our count.
     var count: usize = @max(count_req, 1);
     if (self.screen.cursor.pending_wrap) {
@@ -1365,8 +1374,42 @@ pub fn cursorLeft(self: *Terminal, count_req: usize) void {
         count -= 1;
     }
 
-    // TODO: scroll region
-    self.screen.cursor.x -|= count;
+    // If we are in no wrap mode, then we move the cursor left and exit
+    // since this is the fastest and most typical path.
+    if (wrap_mode == .none) {
+        self.screen.cursor.x -|= count;
+        return;
+    }
+
+    // The leftmost column we can move left to.
+    const left_margin = 0;
+    const right_margin = self.cols - 1;
+    const top = self.scrolling_region.top;
+    //const bottom = self.screen.scroll_region.bottom;
+
+    while (true) {
+        // We can move at most to the left margin.
+        const max = self.screen.cursor.x - left_margin;
+
+        // We want to move at most the number of columns we have left
+        // or our remaining count. Do the move.
+        const amount = @min(max, count);
+        count -= amount;
+        self.screen.cursor.x -= amount;
+
+        // If we have no more to move, then we're done.
+        if (count == 0) break;
+
+        // If we are at the top, then we are done.
+        if (self.screen.cursor.y == top) break;
+
+        // If our previous line is not wrapped then we are done.
+        const row = self.screen.getRow(.{ .active = self.screen.cursor.y - 1 });
+        if (!row.isWrapped()) break;
+        self.screen.cursor.y -= 1;
+        self.screen.cursor.x = right_margin;
+        count -= 1;
+    }
 }
 
 /// Move the cursor right amount columns. If amount is greater than the
@@ -3353,3 +3396,45 @@ test "Terminal: cursorLeft unsets pending wrap state with longer jump" {
         try testing.expectEqualStrings("ABXDE", str);
     }
 }
+
+test "Terminal: cursorLeft reverse wrap" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 5, 5);
+    defer t.deinit(alloc);
+
+    t.modes.set(.wraparound, true);
+    t.modes.set(.reverse_wrap, true);
+
+    for ("ABCDE1") |c| try t.print(c);
+    t.cursorLeft(2);
+    try t.print('X');
+    try testing.expect(t.screen.cursor.pending_wrap);
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("ABCDX\n1", str);
+    }
+}
+
+test "Terminal: cursorLeft reverse wrap with no soft wrap" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 5, 5);
+    defer t.deinit(alloc);
+
+    t.modes.set(.wraparound, true);
+    t.modes.set(.reverse_wrap, true);
+
+    for ("ABCDE") |c| try t.print(c);
+    t.carriageReturn();
+    try t.linefeed();
+    try t.print('1');
+    t.cursorLeft(2);
+    try t.print('X');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("ABCDE\nX", str);
+    }
+}

src/terminal/modes.zig

@@ -170,6 +170,7 @@ const entries: []const ModeEntry = &.{
     .{ .name = "mouse_format_sgr_pixels", .value = 1016 },
     .{ .name = "alt_esc_prefix", .value = 1036, .default = true },
     .{ .name = "alt_sends_escape", .value = 1039 },
+    .{ .name = "reverse_wrap_extended", .value = 1045 },
     .{ .name = "alt_screen_save_cursor_clear_enter", .value = 1049 },
     .{ .name = "bracketed_paste", .value = 2004 },
     .{ .name = "synchronized_output", .value = 2026 },