screen: only use bg attr for inserted rows

When scrolling up or deleting lines (effectively the same operation),
the inserted lines should only inherit the bg attribute of the cursor.
This behavior is similar to erase display and erase line. Update tests
to reflect this behavior.

src/terminal/Screen.zig

@@ -1145,6 +1145,13 @@ pub fn scrollRegionUp(self: *Screen, top: RowIndex, bottom: RowIndex, count_req:
     // The total amount we're going to copy
     const total_copy = (height - count) * (self.cols + 1);
 
+    // The pen we'll use for new cells (only the BG attribute is applied to new
+    // cells)
+    const pen: Cell = if (!self.cursor.pen.attrs.has_bg) .{} else .{
+        .bg = self.cursor.pen.bg,
+        .attrs = .{ .has_bg = true },
+    };
+
     // Fast-path is that we have a contiguous buffer in our circular buffer.
     // In this case we can do some memmoves.
     if (slices[1].len == 0) {
@@ -1170,7 +1177,7 @@ pub fn scrollRegionUp(self: *Screen, top: RowIndex, bottom: RowIndex, count_req:
             // is a lot more of that.
             const dst_offset = total_copy;
             const dst = buf[dst_offset..];
-            @memset(dst, .{ .cell = self.cursor.pen });
+            @memset(dst, .{ .cell = pen });
 
             // Then we make sure our row headers are zeroed out. We set
             // the value to a dirty row header so that the renderer re-draws.
@@ -1250,7 +1257,7 @@ pub fn scrollRegionUp(self: *Screen, top: RowIndex, bottom: RowIndex, count_req:
         if (offset >= slices[i].len) continue;
 
         const dst = slices[i][offset..];
-        @memset(dst, .{ .cell = self.cursor.pen });
+        @memset(dst, .{ .cell = pen });
 
         var j: usize = offset;
         while (j < slices[i].len) : (j += self.cols + 1) {
@@ -4017,12 +4024,19 @@ test "Screen: scrollRegionUp single with pen" {
     try s.testWriteString("1ABCD\n2EFGH\n3IJKL\n4ABCD");
 
     s.cursor.pen = .{ .char = 'X' };
+    s.cursor.pen.bg = .{ .r = 155 };
+    s.cursor.pen.attrs.has_bg = true;
+    s.cursor.pen.attrs.bold = true;
     s.scrollRegionUp(.{ .active = 1 }, .{ .active = 2 }, 1);
     {
         // Test our contents rotated
         var contents = try s.testString(alloc, .screen);
         defer alloc.free(contents);
-        try testing.expectEqualStrings("1ABCD\n3IJKL\nXXXXX\n4ABCD", contents);
+        try testing.expectEqualStrings("1ABCD\n3IJKL\n\n4ABCD", contents);
+        const cell = s.getCell(.active, 2, 0);
+        try testing.expectEqual(@as(u8, 155), cell.bg.r);
+        try testing.expect(!cell.attrs.bold);
+        try testing.expect(s.cursor.pen.attrs.bold);
     }
 }
 
@@ -4085,12 +4099,19 @@ test "Screen: scrollRegionUp fills with pen" {
     try s.testWriteString("A\nB\nC\nD");
 
     s.cursor.pen = .{ .char = 'X' };
+    s.cursor.pen.bg = .{ .r = 155 };
+    s.cursor.pen.attrs.has_bg = true;
+    s.cursor.pen.attrs.bold = true;
     s.scrollRegionUp(.{ .active = 0 }, .{ .active = 2 }, 1);
     {
         // Test our contents rotated
         var contents = try s.testString(alloc, .screen);
         defer alloc.free(contents);
-        try testing.expectEqualStrings("B\nC\nXXXXX\nD", contents);
+        try testing.expectEqualStrings("B\nC\n\nD", contents);
+        const cell = s.getCell(.active, 2, 0);
+        try testing.expectEqual(@as(u8, 155), cell.bg.r);
+        try testing.expect(!cell.attrs.bold);
+        try testing.expect(s.cursor.pen.attrs.bold);
     }
 }
 
@@ -4110,13 +4131,20 @@ test "Screen: scrollRegionUp buffer wrap" {
 
     // Scroll
     s.cursor.pen = .{ .char = 'X' };
+    s.cursor.pen.bg = .{ .r = 155 };
+    s.cursor.pen.attrs.has_bg = true;
+    s.cursor.pen.attrs.bold = true;
     s.scrollRegionUp(.{ .screen = 0 }, .{ .screen = 2 }, 1);
 
     {
         // Test our contents rotated
         var contents = try s.testString(alloc, .screen);
         defer alloc.free(contents);
-        try testing.expectEqualStrings("3IJKL\n4ABCD\nXXXXX", contents);
+        try testing.expectEqualStrings("3IJKL\n4ABCD", contents);
+        const cell = s.getCell(.active, 2, 0);
+        try testing.expectEqual(@as(u8, 155), cell.bg.r);
+        try testing.expect(!cell.attrs.bold);
+        try testing.expect(s.cursor.pen.attrs.bold);
     }
 }
 
@@ -4136,13 +4164,20 @@ test "Screen: scrollRegionUp buffer wrap alternate" {
 
     // Scroll
     s.cursor.pen = .{ .char = 'X' };
+    s.cursor.pen.bg = .{ .r = 155 };
+    s.cursor.pen.attrs.has_bg = true;
+    s.cursor.pen.attrs.bold = true;
     s.scrollRegionUp(.{ .screen = 0 }, .{ .screen = 2 }, 2);
 
     {
         // Test our contents rotated
         var contents = try s.testString(alloc, .screen);
         defer alloc.free(contents);
-        try testing.expectEqualStrings("4ABCD\nXXXXX\nXXXXX", contents);
+        try testing.expectEqualStrings("4ABCD", contents);
+        const cell = s.getCell(.active, 2, 0);
+        try testing.expectEqual(@as(u8, 155), cell.bg.r);
+        try testing.expect(!cell.attrs.bold);
+        try testing.expect(s.cursor.pen.attrs.bold);
     }
 }