screen: winhl=Normal:Background should not override syntax (#8093)

fixes #7375

src/nvim/screen.c

@@ -2044,7 +2044,7 @@ static void fold_line(win_T *wp, long fold_count, foldinfo_T *foldinfo, linenr_T
   }
 
   screen_line(row + wp->w_winrow, wp->w_wincol, wp->w_width,
-              wp->w_width, false, wp);
+              wp->w_width, false, wp, 0);
 
   /*
    * Update w_cline_height and w_cline_folded if the cursor line was
@@ -2465,10 +2465,6 @@ win_line (
     line_attr = win_hl_attr(wp, HLF_QFL);
   }
 
-  if (wp->w_hl_attr_normal != 0) {
-    line_attr = hl_combine_attr(wp->w_hl_attr_normal, line_attr);
-  }
-
   if (line_attr != 0) {
     area_highlighting = true;
   }
@@ -2926,7 +2922,8 @@ win_line (
         && lnum == wp->w_cursor.lnum && vcol >= (long)wp->w_virtcol
         && filler_todo <= 0
         ) {
-      screen_line(screen_row, wp->w_wincol, col, -wp->w_width, wp->w_p_rl, wp);
+      screen_line(screen_row, wp->w_wincol, col, -wp->w_width, wp->w_p_rl, wp,
+                  wp->w_hl_attr_normal);
       // Pretend we have finished updating the window.  Except when
       // 'cursorcolumn' is set.
       if (wp->w_p_cuc) {
@@ -4019,7 +4016,8 @@ win_line (
           col++;
         }
       }
-      screen_line(screen_row, wp->w_wincol, col, wp->w_width, wp->w_p_rl, wp);
+      screen_line(screen_row, wp->w_wincol, col, wp->w_width, wp->w_p_rl, wp,
+                  wp->w_hl_attr_normal);
       row++;
 
       /*
@@ -4242,7 +4240,7 @@ win_line (
             || (n_extra != 0 && (c_extra != NUL || *p_extra != NUL)))
         ) {
       screen_line(screen_row, wp->w_wincol, col - boguscols,
-                  wp->w_width, wp->w_p_rl, wp);
+                  wp->w_width, wp->w_p_rl, wp, wp->w_hl_attr_normal);
       boguscols = 0;
       ++row;
       ++screen_row;
@@ -4412,7 +4410,7 @@ static int char_needs_redraw(int off_from, int off_to, int cols)
  *    When FALSE and "clear_width" > 0, clear columns "endcol" to "clear_width"
  */
 static void screen_line(int row, int coloff, int endcol,
-                        int clear_width, int rlflag, win_T *wp)
+                        int clear_width, int rlflag, win_T *wp, int bg_attr)
 {
   unsigned off_from;
   unsigned off_to;
@@ -4445,15 +4443,16 @@ static void screen_line(int row, int coloff, int endcol,
     /* Clear rest first, because it's left of the text. */
     if (clear_width > 0) {
       while (col <= endcol && ScreenLines[off_to] == ' '
-             && ScreenAttrs[off_to] == 0
+             && ScreenAttrs[off_to] == bg_attr
              && (!enc_utf8 || ScreenLinesUC[off_to] == 0)
              ) {
         ++off_to;
         ++col;
       }
-      if (col <= endcol)
+      if (col <= endcol) {
-        screen_fill(row, row + 1, col + coloff,
+        screen_fill(row, row + 1, col + coloff, endcol + coloff + 1, ' ', ' ',
-            endcol + coloff + 1, ' ', ' ', 0);
+                    bg_attr);
+      }
     }
     col = endcol + 1;
     off_to = LineOffset[row] + col + coloff;
@@ -4461,6 +4460,13 @@ static void screen_line(int row, int coloff, int endcol,
     endcol = (clear_width > 0 ? clear_width : -clear_width);
   }
 
+  if (bg_attr) {
+    for (int c = col; c < endcol; c++) {
+      ScreenAttrs[off_from+c] = hl_combine_attr(bg_attr,
+                                                ScreenAttrs[off_from+c]);
+    }
+  }
+
   redraw_next = char_needs_redraw(off_from, off_to, endcol - col);
 
   while (col < endcol) {
@@ -4559,15 +4565,15 @@ static void screen_line(int row, int coloff, int endcol,
 
     /* blank out the rest of the line */
     while (col < clear_width && ScreenLines[off_to] == ' '
-           && ScreenAttrs[off_to] == 0
+           && ScreenAttrs[off_to] == bg_attr
            && (!enc_utf8 || ScreenLinesUC[off_to] == 0)
            ) {
       ++off_to;
       ++col;
     }
     if (col < clear_width) {
-      screen_fill(row, row + 1, col + coloff, clear_width + coloff,
+      screen_fill(row, row + 1, col + coloff, clear_width + coloff, ' ', ' ',
-          ' ', ' ', 0);
+                  bg_attr);
       off_to += clear_width - col;
       col = clear_width;
     }

test/functional/ui/highlight_spec.lua

@@ -778,6 +778,9 @@ describe("'winhighlight' highlight", function()
       [22] = {bold = true, foreground = Screen.colors.SeaGreen4},
       [23] = {background = Screen.colors.LightMagenta},
       [24] = {background = Screen.colors.WebGray},
+      [25] = {bold = true, foreground = Screen.colors.Green1},
+      [26] = {background = Screen.colors.Red},
+      [27] = {background = Screen.colors.DarkBlue, bold = true, foreground = Screen.colors.Green1},
     })
     command("hi Background1 guibg=DarkBlue")
     command("hi Background2 guibg=DarkGreen")
@@ -1047,6 +1050,39 @@ describe("'winhighlight' highlight", function()
     ]])
   end)
 
+  it("background doesn't override syntax background", function()
+    command('syntax on')
+    command('syntax keyword Foobar foobar')
+    command('syntax keyword Article the')
+    command('hi Foobar guibg=#FF0000')
+    command('hi Article guifg=#00FF00 gui=bold')
+    insert('the foobar was foobar')
+    screen:expect([[
+      {25:the} {26:foobar} was {26:fooba}|
+      {26:^r}                   |
+      {0:~                   }|
+      {0:~                   }|
+      {0:~                   }|
+      {0:~                   }|
+      {0:~                   }|
+                          |
+    ]])
+
+    -- winhl=Normal:Group with background doesn't override syntax background,
+    -- but does combine with syntax foreground.
+    command('set winhl=Normal:Background1')
+    screen:expect([[
+      {27:the}{1: }{26:foobar}{1: was }{26:fooba}|
+      {26:^r}{1:                   }|
+      {2:~                   }|
+      {2:~                   }|
+      {2:~                   }|
+      {2:~                   }|
+      {2:~                   }|
+                          |
+    ]])
+  end)
+
   it('can override NonText, Conceal and EndOfBuffer', function()
     curbufmeths.set_lines(0,-1,true, {"raa\000"})
     command('call matchaddpos("Conceal", [[1,2]], 0, -1, {"conceal": "#"})')