highlight: high-priority CursorLine if fg is set. #8578

closes #7383
closes #7715

This implements the compromise described in #7383:
* low-priority CursorLine if foreground is not set
* high-priority ("same as Vim" priority) CursorLine if foreground is set

ref d1874ab2821d076397290cc154d87ec2dc352c79
ref 56eda2aa17c80ba380b606f9466f288fb8162dd3

4 files changed, 84 insertions, 27 deletions

diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 88b45900a2..83030bf713 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -4841,15 +4841,13 @@ ColorColumn	used for the columns set with 'colorcolumn'
 Conceal		placeholder characters substituted for concealed
 		text (see 'conceallevel')
 							*hl-Cursor*
-Cursor		the character under the cursor
+Cursor		character under the cursor
 							*hl-CursorIM*
 CursorIM	like Cursor, but used when in IME mode |CursorIM|
 							*hl-CursorColumn*
-CursorColumn	the screen column that the cursor is in when 'cursorcolumn' is
-		set
+CursorColumn	screen column at the cursor, when 'cursorcolumn' is set
 							*hl-CursorLine*
-CursorLine	the screen line that the cursor is in when 'cursorline' is
-		set
+CursorLine	screen line at the cursor, when 'cursorline' is set
 							*hl-Directory*
 Directory	directory names (and other special names in listings)
 							*hl-DiffAdd*
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index 52f6b3d918..8bda114639 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -306,6 +306,7 @@ other arguments if used).
 Highlight groups:
   |hl-ColorColumn|, |hl-CursorColumn| are lower priority than most other
   groups
+  |hl-CursorLine| is low-priority unless foreground color is set
 
 Macro/|recording| behavior
   Replay of a macro recorded during :lmap produces the same actions as when it
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 4cb6575502..4c011e466b 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -2173,6 +2173,7 @@ win_line (
   colnr_T trailcol = MAXCOL;            /* start of trailing spaces */
   int need_showbreak = false;           // overlong line, skip first x chars
   int line_attr = 0;                    // attribute for the whole line
+  int line_attr_lowprio = 0;            // low-priority attribute for the line
   matchitem_T *cur;                     // points to the match list
   match_T     *shl;                     // points to search_hl or a match
   int shl_flag;                         // flag to indicate whether search_hl
@@ -2398,6 +2399,29 @@ win_line (
     filler_lines = wp->w_topfill;
   filler_todo = filler_lines;
 
+  // Cursor line highlighting for 'cursorline' in the current window.  Not
+  // when Visual mode is active, because it's not clear what is selected
+  // then.
+  if (wp->w_p_cul && lnum == wp->w_cursor.lnum
+      && !(wp == curwin && VIsual_active)) {
+    int cul_attr = win_hl_attr(wp, HLF_CUL);
+    HlAttrs *aep = syn_cterm_attr2entry(cul_attr);
+
+    // We make a compromise here (#7383):
+    //  * low-priority CursorLine if fg is not set
+    //  * high-priority ("same as Vim" priority) CursorLine if fg is set
+    if (aep->rgb_fg_color == -1 && aep->cterm_fg_color == 0) {
+      line_attr_lowprio = cul_attr;
+    } else {
+      if (line_attr != 0 && !(State & INSERT) && bt_quickfix(wp->w_buffer)
+          && qf_current_entry(wp) == lnum) {
+        line_attr = hl_combine_attr(cul_attr, line_attr);
+      } else {
+        line_attr = cul_attr;
+      }
+    }
+  }
+
   // If this line has a sign with line highlighting set line_attr.
   v = buf_getsigntype(wp->w_buffer, lnum, SIGN_LINEHL);
   if (v != 0) {
@@ -2409,7 +2433,7 @@ win_line (
     line_attr = win_hl_attr(wp, HLF_QFL);
   }
 
-  if (line_attr != 0) {
+  if (line_attr_lowprio || line_attr) {
     area_highlighting = true;
   }
 
@@ -2631,20 +2655,6 @@ win_line (
       cur = cur->next;
   }
 
-  // Cursor line highlighting for 'cursorline' in the current window.  Not
-  // when Visual mode is active, because it's not clear what is selected
-  // then.
-  if (wp->w_p_cul && lnum == wp->w_cursor.lnum
-      && !(wp == curwin && VIsual_active)) {
-    if (line_attr != 0 && !(State & INSERT) && bt_quickfix(wp->w_buffer)
-        && qf_current_entry(wp) == lnum) {
-      line_attr = hl_combine_attr(win_hl_attr(wp, HLF_CUL), line_attr);
-    } else {
-      line_attr = win_hl_attr(wp, HLF_CUL);
-    }
-    area_highlighting = true;
-  }
-
   off = (unsigned)(current_ScreenLine - ScreenLines);
   int col = 0;  // Visual column on screen.
   if (wp->w_p_rl) {
@@ -3567,8 +3577,10 @@ win_line (
           // Display a '$' after the line or highlight an extra
           // character if the line break is included.
           // For a diff line the highlighting continues after the "$".
-          if (diff_hlf == (hlf_T)0 && line_attr == 0) {
-            // In virtualedit, visual selections may extend beyond end of line.
+          if (diff_hlf == (hlf_T)0
+              && line_attr == 0
+              && line_attr_lowprio == 0) {
+            // In virtualedit, visual selections may extend beyond end of line
             if (area_highlighting && virtual_active()
                 && tocol != MAXCOL && vcol < tocol) {
               n_extra = 0;
@@ -3631,7 +3643,7 @@ win_line (
                      (col < wp->w_width))) {
           c = ' ';
           ptr--;  // put it back at the NUL
-        } else if ((diff_hlf != (hlf_T)0 || line_attr != 0)
+        } else if ((diff_hlf != (hlf_T)0 || line_attr_lowprio || line_attr)
                    && (wp->w_p_rl
                        ? (col >= 0)
                        : (col - boguscols < wp->w_width))) {
@@ -3643,7 +3655,8 @@ win_line (
           did_line_attr++;
 
           // don't do search HL for the rest of the line
-          if (line_attr != 0 && char_attr == search_attr && col > 0) {
+          if ((line_attr_lowprio || line_attr)
+              && char_attr == search_attr && col > 0) {
             char_attr = line_attr;
           }
           if (diff_hlf == HLF_TXD) {
@@ -4007,6 +4020,11 @@ win_line (
       }
     }
 
+    // Apply lowest-priority line attr now, so everything can override it.
+    if (draw_state == WL_LINE) {
+      char_attr = hl_combine_attr(line_attr_lowprio, char_attr);
+    }
+
     /*
      * Store character to be displayed.
      * Skip characters that are left of the screen for 'nowrap'.
diff --git a/test/functional/ui/highlight_spec.lua b/test/functional/ui/highlight_spec.lua
index ab3b1c3cac..b46a6c1e46 100644
--- a/test/functional/ui/highlight_spec.lua
+++ b/test/functional/ui/highlight_spec.lua
@@ -541,7 +541,7 @@ describe("'listchars' highlight", function()
     ]])
     feed_command('set cursorline')
     screen:expect([[
-      {2:^>-------.}{1:abcd}{2:.}{1:Lorem}{4:>}|
+      {2:^>-------.}{1:abcd}{2:.}{1:Lorem}{3:>}|
       {5:>-------.}abcd{5:*}{4:¬}     |
       {4:¬}                   |
       {4:~                   }|
@@ -549,7 +549,7 @@ describe("'listchars' highlight", function()
     ]])
     feed('$')
     screen:expect([[
-      {4:<}{1:r}{2:.}{1:sit}{2:.}{1:ame^t}{3:¬}{1:        }|
+      {3:<}{1:r}{2:.}{1:sit}{2:.}{1:ame^t}{3:¬}{1:        }|
       {4:<}                   |
       {4:<}                   |
       {4:~                   }|
@@ -630,7 +630,7 @@ describe("'listchars' highlight", function()
     feed('<esc>$')
     screen:expect([[
       {4:<}                   |
-      {4:<}{1:r}{2:.}{1:sit}{2:.}{1:ame^t}{3:¬}{1:        }|
+      {3:<}{1:r}{2:.}{1:sit}{2:.}{1:ame^t}{3:¬}{1:        }|
       {4:<}                   |
       {4:~                   }|
                           |
@@ -675,6 +675,46 @@ describe("'listchars' highlight", function()
   end)
 end)
 
+describe('CursorLine highlight', function()
+  before_each(clear)
+  it('overridden by Error, ColorColumn if fg not set', function()
+    local screen = Screen.new(50,5)
+    screen:set_default_attr_ids({
+      [1] = {foreground = Screen.colors.SlateBlue},
+      [2] = {bold = true, foreground = Screen.colors.Brown},
+      [3] = {foreground = Screen.colors.Grey100, background = Screen.colors.Red},
+      [4] = {foreground = Screen.colors.SlateBlue, background = Screen.colors.Gray90},
+      [5] = {background = Screen.colors.Gray90},
+      [6] = {bold = true, foreground = Screen.colors.Blue1},
+      [7] = {background = Screen.colors.LightRed},
+    })
+    screen:attach()
+
+    feed_command('filetype on')
+    feed_command('syntax on')
+    feed_command('set cursorline ft=json')
+    feed('i{<cr>"a" : abc // 10;<cr>}<cr><esc>')
+    screen:expect([[
+      {1:{}                                                 |
+      "{2:a}" : {3:abc} {3:// 10;}                                  |
+      {1:}}                                                 |
+      {5:^                                                  }|
+                                                        |
+    ]])
+
+    feed_command('set colorcolumn=3')
+    feed('i  <esc>')
+    screen:expect([[
+      {1:{} {7: }                                               |
+      "{2:a}{7:"} : {3:abc} {3:// 10;}                                  |
+      {1:}} {7: }                                               |
+      {5: ^ }{7: }{5:                                               }|
+                                                        |
+    ]])
+  end)
+end)
+
+
 describe("MsgSeparator highlight and msgsep fillchar", function()
   before_each(clear)
   it("works", function()