fix(api): make getting explicit empty hl in virtual text work (#28697)

src/nvim/api/extmark.c

@@ -121,7 +121,7 @@ Array virt_text_to_array(VirtText vt, bool hl_name, Arena *arena)
     Array hl_array = arena_array(arena, i < j ? j - i + 1 : 0);
     for (; i < j; i++) {
       int hl_id = kv_A(vt, i).hl_id;
-      if (hl_id > 0) {
+      if (hl_id >= 0) {
         ADD_C(hl_array, hl_group_name(hl_id, hl_name));
       }
     }
@@ -131,11 +131,11 @@ Array virt_text_to_array(VirtText vt, bool hl_name, Arena *arena)
     Array chunk = arena_array(arena, 2);
     ADD_C(chunk, CSTR_AS_OBJ(text));
     if (hl_array.size > 0) {
-      if (hl_id > 0) {
+      if (hl_id >= 0) {
         ADD_C(hl_array, hl_group_name(hl_id, hl_name));
       }
       ADD_C(chunk, ARRAY_OBJ(hl_array));
-    } else if (hl_id > 0) {
+    } else if (hl_id >= 0) {
       ADD_C(chunk, hl_group_name(hl_id, hl_name));
     }
     ADD_C(chunks, ARRAY_OBJ(chunk));
@@ -1165,7 +1165,7 @@ VirtText parse_virt_text(Array chunks, Error *err, int *width)
 
     String str = chunk.items[0].data.string;
 
-    int hl_id = 0;
+    int hl_id = -1;
     if (chunk.size == 2) {
       Object hl = chunk.items[1];
       if (hl.type == kObjectTypeArray) {

src/nvim/decoration.c

@@ -346,7 +346,12 @@ char *next_virt_text_chunk(VirtText vt, size_t *pos, int *attr)
   for (; text == NULL && *pos < kv_size(vt); (*pos)++) {
     text = kv_A(vt, *pos).text;
     int hl_id = kv_A(vt, *pos).hl_id;
-    *attr = hl_combine_attr(*attr, hl_id > 0 ? syn_id2attr(hl_id) : 0);
+    if (hl_id >= 0) {
+      *attr = MAX(*attr, 0);
+      if (hl_id > 0) {
+        *attr = hl_combine_attr(*attr, syn_id2attr(hl_id));
+      }
+    }
   }
   return text;
 }

src/nvim/decoration_defs.h

@@ -10,7 +10,7 @@
 
 typedef struct {
   char *text;
-  int hl_id;
+  int hl_id;  ///< -1 if not specified
 } VirtTextChunk;
 
 typedef kvec_t(VirtTextChunk) VirtText;

test/functional/api/extmark_spec.lua

@@ -1569,7 +1569,7 @@ describe('API/extmarks', function()
       sign_text = '>>',
       spell = true,
       virt_lines = {
-        { { 'lines', 'Macro' }, { '???' } },
+        { { 'lines', 'Macro' }, { '???' }, { ';;;', '' } },
         { { 'stack', { 'Type', 'Search' } }, { '!!!' } },
       },
       virt_lines_above = true,
@@ -1604,7 +1604,7 @@ describe('API/extmarks', function()
         sign_text = '>>',
         spell = true,
         virt_lines = {
-          { { 'lines', 'Macro' }, { '???' } },
+          { { 'lines', 'Macro' }, { '???' }, { ';;;', '' } },
           { { 'stack', { 'Type', 'Search' } }, { '!!!' } },
         },
         virt_lines_above = true,

test/functional/ui/float_spec.lua

@@ -2407,6 +2407,7 @@ describe('float window', function()
 
       command('hi B0 guibg=Red guifg=Black')
       command('hi B1 guifg=White')
+
       api.nvim_win_set_config(win, {
         title = {{"🦄"}, {"BB", {"B0", "B1"}}}, title_pos = "right",
         footer= {{"🦄"}, {"BB", {"B0", "B1"}}}, footer_pos = "right",
@@ -2443,6 +2444,47 @@ describe('float window', function()
                                                   |
         ]]}
       end
+      eq({{"🦄"}, {"BB", {"B0", "B1"}}}, api.nvim_win_get_config(win).title)
+      eq({{"🦄"}, {"BB", {"B0", "B1"}}}, api.nvim_win_get_config(win).footer)
+
+      api.nvim_win_set_config(win, {
+        title = {{"🦄", ""}, {"BB", {"B0", "B1", ""}}}, title_pos = "left",
+        footer= {{"🦄", ""}, {"BB", {"B0", "B1", ""}}}, footer_pos = "left",
+      })
+      if multigrid then
+        screen:expect{grid=[[
+        ## grid 1
+          [2:----------------------------------------]|*6
+          [3:----------------------------------------]|
+        ## grid 2
+          ^                                        |
+          {0:~                                       }|*5
+        ## grid 3
+                                                  |
+        ## grid 4
+          {5:╔}🦄{7:BB}{5:═════╗}|
+          {5:║}{1: halloj! }{5:║}|
+          {5:║}{1: BORDAA  }{5:║}|
+          {5:╚}🦄{7:BB}{5:═════╝}|
+        ]], float_pos={
+          [4] = { 1001, "NW", 1, 2, 5, true }
+        }, win_viewport={
+          [2] = {win = 1000, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+          [4] = {win = 1001, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 2, sum_scroll_delta = 0};
+        }}
+      else
+        screen:expect{grid=[[
+          ^                                        |
+          {0:~                                       }|
+          {0:~    }{5:╔}🦄{7:BB}{5:═════╗}{0:                        }|
+          {0:~    }{5:║}{1: halloj! }{5:║}{0:                        }|
+          {0:~    }{5:║}{1: BORDAA  }{5:║}{0:                        }|
+          {0:~    }{5:╚}🦄{7:BB}{5:═════╝}{0:                        }|
+                                                  |
+        ]]}
+      end
+      eq({{"🦄", ""}, {"BB", {"B0", "B1", ""}}}, api.nvim_win_get_config(win).title)
+      eq({{"🦄", ""}, {"BB", {"B0", "B1", ""}}}, api.nvim_win_get_config(win).footer)
     end)
 
     it('terminates border on edge of viewport when window extends past viewport', function()