formatter: blank cells carry only across a joined wrap, not after a line break

.github/workflows/next-xcframework.yml

@@ -138,6 +138,9 @@ jobs:
             -Dtest-filter="Page vt preserved trailing blank rows" \
             -Dtest-filter="Page VT preserves a fully styled blank row" \
             -Dtest-filter="Page VT unstyled blank cells" \
+            -Dtest-filter="Page plain wrap continuation" \
+            -Dtest-filter="breaks the wrap" \
+            -Dtest-filter="print wrap at the scroll region bottom" \
             -Dtest-filter="render: OSC dynamic color resets" \
             -Dtest-filter="get cursor visual" \
             -Dtest-filter="cursor activity" \

src/terminal/Screen.zig

@@ -1185,6 +1185,10 @@ pub fn cursorScrollAbove(self: *Screen) !void {
         }
     }
 
+    // The rows below the cursor did not move but the cursor row is a new
+    // blank row: the row below no longer continues it.
+    self.breakWrapAbove(self.cursor.page_pin.down(1).?);
+
     if (self.cursor.style_id != style.default_id) {
         // The newly created line needs to be styled according to
         // the bg color if it is set.
@@ -1297,7 +1301,9 @@ fn cursorScrollAboveRotate(
 /// other scroll operations such as deleteLines).
 ///
 /// The cursor stays at the same screen position (the new blank row).
-/// Content outside of the region is unmodified.
+/// Content outside of the region is unmodified, but a soft wrap that
+/// joined a row outside the region to one inside it is broken (see
+/// breakWrapAbove): those rows no longer hold one line.
 ///
 /// This is a very hot path for scroll region usage (e.g. a program
 /// on the alt screen using DECSTBM and scrolling via LF/IND) so this
@@ -1313,7 +1319,11 @@ pub fn cursorScrollRegionUp(self: *Screen, limit: usize) !void {
     // If the region crosses a page boundary we take a slower path. This
     // is rare: it requires the active area to span multiple pages with
     // the split point inside the scroll region.
-    if (pin.y < limit) return try self.cursorScrollRegionUpSlow(limit);
+    if (pin.y < limit) {
+        try self.cursorScrollRegionUpSlow(limit);
+        self.breakWrapAtScrolledRegionEdges(limit);
+        return;
+    }
 
     // Fast path: the entire region is in a single page. We can clear
     // the top row and rotate it down to the cursor row, updating any
@@ -1399,6 +1409,20 @@ pub fn cursorScrollRegionUp(self: *Screen, limit: usize) !void {
     const cursor_row: *Row = &rows[limit];
     self.cursor.page_row = cursor_row;
     self.cursor.page_cell = &page.getCells(cursor_row)[self.cursor.x];
+
+    self.breakWrapAtScrolledRegionEdges(limit);
+}
+
+/// After cursorScrollRegionUp: the region from `limit` rows above the
+/// cursor to the cursor row moved, the rows above and below it did not,
+/// so no soft wrap may join a row outside the region to one inside it.
+fn breakWrapAtScrolledRegionEdges(self: *Screen, limit: usize) void {
+    if (self.cursor.y > limit) {
+        self.breakWrapAbove(self.cursor.page_pin.up(limit).?);
+    }
+    if (self.cursor.y + 1 < self.pages.rows) {
+        self.breakWrapAbove(self.cursor.page_pin.down(1).?);
+    }
 }
 
 /// Slow path for cursorScrollRegionUp: the scroll region spans
@@ -1651,6 +1675,32 @@ pub fn cursorResetWrap(self: *Screen) void {
     }
 }
 
+/// Break the soft wrap between the row at `pin` and the row above it,
+/// if either row's flag says they are joined. A scroll of a scroll region
+/// moves the rows on one side of its edge and not the other, so the two
+/// rows no longer hold one line; a stale wrap or wrap_continuation would
+/// make reflow and the unwrapping formatter join them. The row above may
+/// be a scrollback row.
+pub fn breakWrapAbove(self: *Screen, pin: Pin) void {
+    const row = pin.rowAndCell().row;
+    const prev = pin.up(1) orelse {
+        row.wrap_continuation = false;
+        return;
+    };
+    const prev_row = prev.rowAndCell().row;
+    if (!row.wrap_continuation and !prev_row.wrap) return;
+    row.wrap_continuation = false;
+    prev_row.wrap = false;
+
+    // A spacer head only exists to carry a wide character over the wrap.
+    const cells = prev.cells(.all);
+    const last = prev.node.cols() - 1;
+    if (cells[last].wide == .spacer_head) {
+        self.clearCells(prev.node.page(), prev_row, cells[last..][0..1]);
+        prev.markDirty();
+    }
+}
+
 /// Make the cursor row start a new logical line by resetting the soft wrap
 /// from the row above into it. Reflow then never joins the two rows.
 pub fn cursorBreakWrapIntoRow(self: *Screen) void {

src/terminal/Terminal.zig

@@ -1810,7 +1810,7 @@ fn printWrap(self: *Terminal) !void {
     const old_semantic_clear = cursor.semantic_content_clear_eol;
 
     // Move to the next line
-    try self.index();
+    try self.indexOpts(true);
     self.screens.active.cursorHorizontalAbsolute(self.scrolling_region.left);
 
     // Our pointer should never move
@@ -2384,6 +2384,12 @@ pub fn tabReset(self: *Terminal) void {
 ///
 /// This unsets the pending wrap state without wrapping.
 pub fn index(self: *Terminal) !void {
+    return self.indexOpts(false);
+}
+
+/// index(), and for `soft_wrap` (printWrap) the cursor row keeps the wrap
+/// printWrap set on it: the row it wraps into is the one the scroll makes.
+fn indexOpts(self: *Terminal, comptime soft_wrap: bool) !void {
     const screen: *Screen = self.screens.active;
 
     // Unset pending wrap state
@@ -2443,6 +2449,12 @@ pub fn index(self: *Terminal) !void {
             screen.kitty_images.dirty = true;
         }
 
+        // A linefeed at a bottom margin moves the cursor row up and away
+        // from the row below the region: a soft wrap from it into that row
+        // no longer joins one line. printWrap's own wrap goes into the new
+        // row the scroll makes, so it stays.
+        if (!soft_wrap) self.breakWrapAtBottomMargin();
+
         // If our scrolling region is at the top, we create scrollback,
         // but only if our screen retains scrollback. If our screen
         // doesn't retain scrollback (e.g. the alternate screen) then
@@ -2508,6 +2520,16 @@ pub fn index(self: *Terminal) !void {
     }
 }
 
+/// Before a scroll that moves the cursor row (the bottom of a full-width
+/// region with rows below it) up: break the cursor row's soft wrap into the
+/// row below the region, which does not move.
+fn breakWrapAtBottomMargin(self: *Terminal) void {
+    if (self.scrolling_region.bottom + 1 >= self.rows or
+        self.scrolling_region.left != 0 or
+        self.scrolling_region.right != self.cols - 1) return;
+    self.screens.active.cursorResetWrap();
+}
+
 /// The operation when we have Kitty image placements during index.
 /// Split out of index() so its hot paths don't carry the adjustment
 /// state in their stack frame, which measurably slows the scroll
@@ -2795,6 +2817,7 @@ pub fn scrollUp(self: *Terminal, count: usize) !void {
         // Move our cursor to the bottom of the scroll region so we can
         // use the cursorScrollAbove function to create scrollback
         self.screens.active.cursorAbsolute(0, self.scrolling_region.bottom);
+        self.breakWrapAtBottomMargin();
         for (0..adjusted_count) |_| try self.screens.active.cursorScrollAbove();
         return;
     }
@@ -2995,6 +3018,18 @@ fn invalidateFullWidthRowRange(
     }
 }
 
+/// After insertLines or deleteLines with a full-width scroll region: the
+/// rows from `top` to the region bottom moved, the rows above and below
+/// them did not, so no soft wrap may join a row outside to one inside.
+fn breakWrapAtLineEdges(self: *Terminal, top: size.CellCountInt) void {
+    const screen: *Screen = self.screens.active;
+    screen.breakWrapAbove(screen.pages.pin(.{ .active = .{ .y = top } }).?);
+    const bottom = self.scrolling_region.bottom;
+    if (bottom + 1 < self.rows) screen.breakWrapAbove(
+        screen.pages.pin(.{ .active = .{ .y = bottom + 1 } }).?,
+    );
+}
+
 // TODO(qwerasd): `insertLines` and `deleteLines` are 99% identical,
 // the majority of their logic can (and should) be abstracted in to
 // a single shared helper function, probably on `Screen` not here.
@@ -3174,6 +3209,8 @@ pub fn insertLines(self: *Terminal, count: usize) void {
         // Move our pin up to the next row.
         if (cur_p.up(1)) |p| cur_p.* = p;
     }
+
+    if (!left_right) self.breakWrapAtLineEdges(start_y);
 }
 
 /// Removes amount lines from the current cursor row down. The remaining lines
@@ -3342,6 +3379,8 @@ pub fn deleteLines(self: *Terminal, count: usize) void {
         // Move our pin down to the next row.
         if (cur_p.down(1)) |p| cur_p.* = p;
     }
+
+    if (!left_right) self.breakWrapAtLineEdges(start_y);
 }
 
 /// Inserts spaces at current cursor position moving existing cell contents
@@ -16908,6 +16947,171 @@ test "Terminal: scroll region linefeed recycled row has default metadata" {
     }
 }
 
+// A scroll of a scroll region moves the rows inside it and keeps the rows
+// outside it. A soft wrap between a row outside and a row inside then joins
+// two rows that no longer hold one line: the outside row's wrap flag (above
+// the region) or wrap_continuation flag (below it) is stale. Reflow and the
+// unwrapping formatter read those flags, so each edge must be broken.
+fn testRowFlags(t: *Terminal, y: u32) struct { wrap: bool, cont: bool } {
+    const row = t.screens.active.pages.getCell(.{ .active = .{ .y = y } }).?.row;
+    return .{ .wrap = row.wrap, .cont = row.wrap_continuation };
+}
+
+test "Terminal: index at the scroll region bottom breaks the wrap into the row below" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 2 soft-wraps into row 3.
+    t.setCursorPos(3, 1);
+    try t.printString("abcdefg");
+    try testing.expect(testRowFlags(&t, 3).cont);
+
+    // DECSTBM rows 2-3 (rows 1-2 here), then a linefeed at its bottom:
+    // row 2 becomes a blank row and row 3, outside the region, stays.
+    t.setTopAndBottomMargin(2, 3);
+    t.setCursorPos(3, 1);
+    try t.linefeed();
+
+    // Row 2's content moved to row 1; row 3 did not move.
+    try testing.expect(!testRowFlags(&t, 1).wrap);
+    try testing.expect(!testRowFlags(&t, 2).wrap);
+    try testing.expect(!testRowFlags(&t, 2).cont);
+    try testing.expect(!testRowFlags(&t, 3).cont);
+}
+
+test "Terminal: print wrap at the scroll region bottom keeps its own wrap and breaks the one below" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 2 soft-wraps into row 3.
+    t.setCursorPos(3, 1);
+    try t.printString("abcdefg");
+    try testing.expect(testRowFlags(&t, 3).cont);
+
+    // DECSTBM rows 2-3 (rows 1-2 here). A wide character at row 2's last
+    // column does not fit, so row 2 gets a spacer head and soft-wraps; the
+    // wrap scrolls the region and row 2 moves to row 1.
+    t.setTopAndBottomMargin(2, 3);
+    t.setCursorPos(3, 5);
+    try t.print(0x6F22); // 漢
+
+    // Row 1 (the moved row) wraps into the new row 2, with its spacer head.
+    try testing.expect(testRowFlags(&t, 1).wrap);
+    try testing.expect(testRowFlags(&t, 2).cont);
+    {
+        const cell = t.screens.active.pages.getCell(.{ .active = .{ .x = 4, .y = 1 } }).?.cell;
+        try testing.expectEqual(Cell.Wide.spacer_head, cell.wide);
+    }
+    // Row 3 does not move and no longer continues anything.
+    try testing.expect(!testRowFlags(&t, 3).cont);
+}
+
+test "Terminal: index in a scroll region breaks the wrap across the region top" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 0 soft-wraps into row 1.
+    t.setCursorPos(1, 1);
+    try t.printString("abcdefg");
+    try testing.expect(testRowFlags(&t, 0).wrap);
+
+    // DECSTBM rows 2-4 (rows 1-3 here): row 1 is discarded and row 0,
+    // outside the region, stays.
+    t.setTopAndBottomMargin(2, 4);
+    t.setCursorPos(4, 1);
+    try t.linefeed();
+
+    try testing.expect(!testRowFlags(&t, 0).wrap);
+    try testing.expect(!testRowFlags(&t, 1).cont);
+}
+
+test "Terminal: index at a bottom margin with scrollback breaks the wrap into the row below" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 1 soft-wraps into row 2.
+    t.setCursorPos(2, 1);
+    try t.printString("abcdefg");
+    try testing.expect(testRowFlags(&t, 2).cont);
+
+    // DECSTBM rows 1-2 (rows 0-1 here) scrolls into the scrollback; row 1
+    // becomes a blank row and row 2, outside the region, stays.
+    t.setTopAndBottomMargin(1, 2);
+    t.setCursorPos(2, 1);
+    try t.linefeed();
+
+    // Row 1's content moved to row 0; row 2 did not move.
+    try testing.expect(!testRowFlags(&t, 0).wrap);
+    try testing.expect(!testRowFlags(&t, 1).wrap);
+    try testing.expect(!testRowFlags(&t, 2).cont);
+}
+
+test "Terminal: scrollUp at a bottom margin breaks the wrap into the row below" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 2 soft-wraps into row 3.
+    t.setCursorPos(3, 1);
+    try t.printString("abcdefg");
+
+    // DECSTBM rows 1-3 (rows 0-2 here), SU 1: row 2's content moves to
+    // row 1 and row 3 does not move.
+    t.setTopAndBottomMargin(1, 3);
+    try t.scrollUp(1);
+
+    try testing.expect(!testRowFlags(&t, 1).wrap);
+    try testing.expect(!testRowFlags(&t, 3).cont);
+}
+
+test "Terminal: deleteLines breaks the wrap across both region edges" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 0 soft-wraps into row 1 and row 3 soft-wraps into row 4.
+    t.setCursorPos(1, 1);
+    try t.printString("abcdefg");
+    t.setCursorPos(4, 1);
+    try t.printString("hijklmn");
+
+    // DECSTBM rows 2-4 (rows 1-3 here), delete the region's top line.
+    t.setTopAndBottomMargin(2, 4);
+    t.setCursorPos(2, 1);
+    t.deleteLines(1);
+
+    try testing.expect(!testRowFlags(&t, 0).wrap);
+    try testing.expect(!testRowFlags(&t, 1).cont);
+    try testing.expect(!testRowFlags(&t, 3).wrap);
+    try testing.expect(!testRowFlags(&t, 4).cont);
+}
+
+test "Terminal: insertLines breaks the wrap across both region edges" {
+    const alloc = testing.allocator;
+    var t = try init(testing.io, alloc, .{ .cols = 5, .rows = 6 });
+    defer t.deinit(alloc);
+
+    // Row 0 soft-wraps into row 1 and row 3 soft-wraps into row 4.
+    t.setCursorPos(1, 1);
+    try t.printString("abcdefg");
+    t.setCursorPos(4, 1);
+    try t.printString("hijklmn");
+
+    // DECSTBM rows 2-4 (rows 1-3 here), insert a line at the region's top.
+    t.setTopAndBottomMargin(2, 4);
+    t.setCursorPos(2, 1);
+    t.insertLines(1);
+
+    try testing.expect(!testRowFlags(&t, 0).wrap);
+    try testing.expect(!testRowFlags(&t, 1).cont);
+    try testing.expect(!testRowFlags(&t, 3).wrap);
+    try testing.expect(!testRowFlags(&t, 4).cont);
+}
+
 test "Terminal: alt screen scroll up recycled row has default metadata" {
     const alloc = testing.allocator;
     const io_impl = testing.io;