fix(options): vim.opt_local:remove({...}) ignored for flag lists #42001

Problem:
vim.opt_local.formatoptions:remove({ 'c', 'r', 'o' }) silently does
nothing since f34ee3da.

Solution:
Join an Array with no separator for a bare flag list, matching the Dict
branch in optval_from_obj().

AI-assisted

src/nvim/option.c

@@ -3841,7 +3841,8 @@ Object optval_from_obj(OptIndex opt_idx, Object o, set_op_T op, bool *error)
         GA_APPEND(char *, &ga, xstrdup(item.data.string.data));
       }
     }
-    str = ga_concat_strings(&ga, ",");
+    // A bare flag list is concatenated with no separator, as in the Dict branch below.
+    str = ga_concat_strings(&ga, (is_flaglist && !is_comma) ? "" : ",");
     GA_DEEP_CLEAR_PTR(&ga);
   } else {  // kObjectTypeDict
     garray_T ga;

test/functional/lua/option_and_var_spec.lua

@@ -1057,6 +1057,14 @@ describe('lua stdlib', function()
         end)
       end)
 
+      it('removes flags from a set when calling remove with a table: #41953', function()
+        eq_exec_lua({ j = true, q = true, l = true }, function()
+          vim.opt.formatoptions = 'jcroql'
+          vim.opt.formatoptions:remove { 'c', 'r', 'o' }
+          return vim.opt.formatoptions:get()
+        end)
+      end)
+
       it('automatically sets when calling append', function()
         eq_exec_lua('foo,bar,baz,bing', function()
           vim.opt.wildignore = 'foo,bar,baz'
@@ -1380,6 +1388,14 @@ describe('lua stdlib', function()
           return vim.bo.tags
         end)
       end)
+
+      it('removes a table of flags from a flag-list option: #41953', function()
+        eq_exec_lua('jql', function()
+          vim.opt_local.formatoptions = 'jcroql'
+          vim.opt_local.formatoptions:remove { 'c', 'r', 'o' }
+          return vim.bo.formatoptions
+        end)
+      end)
     end)
 
     describe('vim.opt_global', function()