screen.c: Allow showbreak to override cursorline. (#13372)

I also added relevant tests.

Close #13369

src/nvim/screen.c

@@ -2836,9 +2836,9 @@ static int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow,
            * required when 'linebreak' is also set. */
           if (tocol == vcol)
             tocol += n_extra;
-          /* combine 'showbreak' with 'cursorline' */
+          // Combine 'showbreak' with 'cursorline', prioritizing 'showbreak'.
           if (wp->w_p_cul && lnum == wp->w_cursor.lnum) {
-            char_attr = hl_combine_attr(char_attr, win_hl_attr(wp, HLF_CUL));
+            char_attr = hl_combine_attr(win_hl_attr(wp, HLF_CUL), char_attr);
           }
         }
       }

test/functional/ui/highlight_spec.lua

@@ -604,7 +604,7 @@ describe("'listchars' highlight", function()
     ]])
   end)
 
-  it("'cursorline' and with 'listchar' option: space, eol, tab, and trail", function()
+  it("'cursorline' and with 'listchars' option", function()
     screen:set_default_attr_ids({
       [1] = {background=Screen.colors.Grey90},
       [2] = {
@@ -861,6 +861,57 @@ describe('CursorLine highlight', function()
     ]])
   end)
 
+  it("overridden by NonText in 'showbreak' characters", function()
+    local screen = Screen.new(20,5)
+    screen:set_default_attr_ids({
+      [1] = {foreground = Screen.colors.Yellow, background = Screen.colors.Blue};
+      [2] = {foreground = Screen.colors.Black, background = Screen.colors.White};
+      [3] = {foreground = Screen.colors.Yellow, background = Screen.colors.White};
+      [4] = {foreground = Screen.colors.Yellow};
+    })
+    screen:attach()
+
+    feed_command('set wrap cursorline')
+    feed_command('set showbreak=>>>')
+    feed_command('highlight clear NonText')
+    feed_command('highlight clear CursorLine')
+    feed_command('highlight NonText guifg=Yellow guibg=Blue gui=NONE')
+    feed_command('highlight CursorLine guifg=Black guibg=White gui=NONE')
+
+    feed('30iø<esc>o<esc>30ia<esc>')
+    screen:expect([[
+      øøøøøøøøøøøøøøøøøøøø|
+      {1:>>>}øøøøøøøøøø       |
+      {2:aaaaaaaaaaaaaaaaaaaa}|
+      {1:>>>}{2:aaaaaaaaa^a       }|
+                          |
+    ]])
+    feed('k')
+    screen:expect([[
+      {2:øøøøøøøøøøøøøøøøøøøø}|
+      {1:>>>}{2:øøøøøøøøø^ø       }|
+      aaaaaaaaaaaaaaaaaaaa|
+      {1:>>>}aaaaaaaaaa       |
+                          |
+    ]])
+    feed_command('highlight NonText guibg=NONE')
+    screen:expect([[
+      {2:øøøøøøøøøøøøøøøøøøøø}|
+      {3:>>>}{2:øøøøøøøøø^ø       }|
+      aaaaaaaaaaaaaaaaaaaa|
+      {4:>>>}aaaaaaaaaa       |
+                          |
+    ]])
+    feed_command('set nocursorline')
+    screen:expect([[
+      øøøøøøøøøøøøøøøøøøøø|
+      {4:>>>}øøøøøøøøø^ø       |
+      aaaaaaaaaaaaaaaaaaaa|
+      {4:>>>}aaaaaaaaaa       |
+      :set nocursorline   |
+    ]])
+  end)
+
   it('always updated. vim-patch:8.1.0849', function()
     local screen = Screen.new(50,5)
     screen:set_default_attr_ids({