fix(extmarks): fix win_col virt_text drawn on wrong screen line (#25264)

src/nvim/decoration.c

@@ -254,7 +254,7 @@ static void decor_add(DecorState *state, int start_row, int start_col, int end_r
 
   DecorRange range = { start_row, start_col, end_row, end_col,
                        *decor, attr_id,
-                       kv_size(decor->virt_text) && owned, -1, ns_id, mark_id };
+                       kv_size(decor->virt_text) && owned, -10, ns_id, mark_id };
 
   kv_pushp(state->active);
   size_t index;
@@ -268,10 +268,10 @@ static void decor_add(DecorState *state, int start_row, int start_col, int end_r
   kv_A(state->active, index) = range;
 }
 
-/// Initialize the draw_col of a newly-added non-inline virtual text item.
+/// Initialize the draw_col of a newly-added virtual text item.
 static void decor_init_draw_col(int win_col, bool hidden, DecorRange *item)
 {
-  if (win_col < 0) {
+  if (win_col < 0 && item->decor.virt_text_pos != kVTInline) {
     item->draw_col = win_col;
   } else if (item->decor.virt_text_pos == kVTOverlay) {
     item->draw_col = (item->decor.virt_text_hide && hidden) ? INT_MIN : win_col;
@@ -371,8 +371,7 @@ next_mark:
       spell = item.decor.spell;
     }
     if (item.start_row == state->row && item.start_col <= col
-        && decor_virt_pos(&item.decor) && item.draw_col == -1
+        && decor_virt_pos(&item.decor) && item.draw_col == -10) {
-        && item.decor.virt_text_pos != kVTInline) {
       decor_init_draw_col(win_col, hidden, &item);
     }
     if (keep) {

src/nvim/decoration.h

@@ -85,6 +85,7 @@ typedef struct {
   /// Screen column to draw the virtual text.
   /// When -1, the virtual text may be drawn after deciding where.
   /// When -3, the virtual text should be drawn on the next screen line.
+  /// When -10, the virtual text has just been added.
   /// When INT_MIN, the virtual text should no longer be drawn.
   int draw_col;
   uint64_t ns_id;

test/functional/ui/decorations_spec.lua

@@ -1237,6 +1237,25 @@ describe('extmark decorations', function()
                                                         |
     ]]}
 
+    meths.buf_set_extmark(0, ns, 4, 50, { virt_text={{'EOL', 'NonText'}} })
+    screen:expect{grid=[[
+      for _,item in ipairs(items) do                    |
+          local text, hl_id_cell, cou{4:Very} unpack(ite{4:VERY}|
+          if                                            |
+      hl_id_cell ~= nil then         {4:Much}           {4:MUCH}|
+              --^ -- -- -- -- -- -- --{4:Error}- -- hl_i{4:ERROR}|
+      l_id_cell {1:EOL}                                     |
+          end                                           |
+          for _ = 1, (count or 1) do                    |
+              local cell = line[colpos]                 |
+          {1:-}   cell.text = text                         {1:-}|
+              cell.hl_id = hl_id                        |
+              colpos = colpos+1                         |
+          end                                           |
+      end                                               |
+                                                        |
+    ]]}
+
     feed '.'
     screen:expect{grid=[[
       for _,item in ipairs(items) do                    |
@@ -1244,7 +1263,7 @@ describe('extmark decorations', function()
           if                                            |
       hl_id_cell ~= nil then         {4:Much}           {4:MUCH}|
               --^ -- -- -- -- -- -- -- -- -- -- -- hl_id |
-      = hl_id_cell                   {4:Error}         {4:ERROR}|
+      = hl_id_cell {1:EOL}               {4:Error}         {4:ERROR}|
           end                                           |
           for _ = 1, (count or 1) do                    |
               local cell = line[colpos]                 |
@@ -1264,7 +1283,7 @@ describe('extmark decorations', function()
       {2:  3 }    if                                        |
       {2:  4 }hl_id_cell ~= nil then         {4:Much}       {4:MUCH}|
       {2:  5 }        --^ -- -- -- -- -- -- -- -- -- -- -- hl|
-      {2:    }_id = hl_id_cell               {4:Error}     {4:ERROR}|
+      {2:    }_id = hl_id_cell {1:EOL}           {4:Error}     {4:ERROR}|
       {2:  6 }    end                                       |
       {2:  7 }    for _ = 1, (count or 1) do                |
       {2:  8 }        local cell = line[colpos]             |
@@ -1283,7 +1302,7 @@ describe('extmark decorations', function()
       {2:  3 }    if                                        |
       {2:  4 }hl_id_cell ~= nil then         {4:Much}       {4:MUCH}|
       {2:  5 }        --^ -- -- -- -- -- -- -- -- -- -- -- hl|
-      _id = hl_id_cell               {4:Error}         {4:ERROR}|
+      _id = hl_id_cell {1:EOL}           {4:Error}         {4:ERROR}|
       {2:  6 }    end                                       |
       {2:  7 }    for _ = 1, (count or 1) do                |
       {2:  8 }        local cell = line[colpos]             |