fix(api): count parameter in nvim_parse_cmd, nvim_cmd #34253

Problem:
- nvim_parse_cmd('copen', {}) returns count: 0, causing nvim_cmd to override default behavior
- nvim_cmd({cmd = 'copen', args = {10}}, {}) fails with "Wrong number of arguments"

Solution:
- Only include count field in parse result when explicitly provided or non-zero
- Interpret single numeric argument as count for count-only commands like copen

src/nvim/api/command.c

@@ -165,8 +165,13 @@ Dict(cmd) nvim_parse_cmd(String str, Dict(empty) *opts, Arena *arena, Error *err
 
   if (ea.argt & EX_COUNT) {
     Integer count = ea.addr_count > 0 ? ea.line2 : (cmd != NULL ? cmd->uc_def : 0);
+    // For built-in commands, if count is not explicitly provided and the default value is 0,
+    // do not include the count field in the result, so the command uses its built-in default
+    // behavior.
+    if (ea.addr_count > 0 || (cmd != NULL && cmd->uc_def != 0) || count != 0) {
       PUT_KEY(result, cmd, count, count);
     }
+  }
 
   if (ea.argt & EX_REGSTR) {
     char reg[2] = { (char)ea.regname, NUL };
@@ -377,8 +382,41 @@ String nvim_cmd(uint64_t channel_id, Dict(cmd) *cmd, Dict(cmd_opts) *opts, Arena
     ea.argt = get_cmd_argt(ea.cmdidx);
   }
 
+  // Track whether the first argument was interpreted as count to avoid conflicts
+  bool count_from_first_arg = false;
   // Parse command arguments since it's needed to get the command address type.
   if (HAS_KEY(cmd, cmd, args)) {
+    // Special handling: for commands that support count but not regular arguments,
+    // if a single numeric argument is provided, interpret it as count
+    if (cmd->args.size == 1 && (ea.argt & EX_COUNT) && !(ea.argt & EX_EXTRA)) {
+      Object first_arg = cmd->args.items[0];
+      bool is_numeric = false;
+      int64_t count_value = 0;
+
+      if (first_arg.type == kObjectTypeInteger) {
+        is_numeric = true;
+        count_value = first_arg.data.integer;
+      } else if (first_arg.type == kObjectTypeString) {
+        // Try to parse string as a number Example: vim.api.nvim_cmd({cmd = 'copen', args = {'10'}}, {})
+        char *endptr;
+        long val = strtol(first_arg.data.string.data, &endptr, 10);
+        // Check if entire string was consumed (valid number) and string is not empty
+        if (*endptr == '\0' && first_arg.data.string.size > 0) {
+          is_numeric = true;
+          count_value = val;
+        }
+      }
+
+      if (is_numeric && count_value >= 0) {
+        // Interpret the argument as count
+        count_from_first_arg = true;
+        ea.addr_count = 1;
+        ea.line1 = ea.line2 = (linenr_T)count_value;
+        args = arena_array(arena, 0);
+      }
+    }
+
+    if (!count_from_first_arg) {
       // Process all arguments. Convert non-String arguments to String and check if String arguments
       // have non-whitespace characters.
       args = arena_array(arena, cmd->args.size);
@@ -440,6 +478,7 @@ String nvim_cmd(uint64_t channel_id, Dict(cmd) *cmd, Dict(cmd_opts) *opts, Arena
         goto end;
       });
     }
+  }
 
   // Simply pass the first argument (if it exists) as the arg pointer to `set_cmd_addr_type()`
   // since it only ever checks the first argument.
@@ -485,6 +524,9 @@ String nvim_cmd(uint64_t channel_id, Dict(cmd) *cmd, Dict(cmd_opts) *opts, Arena
   }
 
   if (HAS_KEY(cmd, cmd, count)) {
+    VALIDATE(!count_from_first_arg, "%s", "Cannot specify both 'count' and numeric argument", {
+      goto end;
+    });
     VALIDATE_MOD((ea.argt & EX_COUNT), "count", cmd->cmd.data);
     VALIDATE_EXP((cmd->count >= 0), "count", "non-negative Integer", NULL, {
       goto end;

test/functional/api/vim_spec.lua

@@ -4783,6 +4783,14 @@ describe('API', function()
       )
       eq('', eval('v:errmsg'))
     end)
+    it('does not include count field when no count provided for builtin commands', function()
+      local result = api.nvim_parse_cmd('copen', {})
+      eq(nil, result.count)
+      api.nvim_cmd(result, {})
+      eq(10, api.nvim_win_get_height(0))
+      result = api.nvim_parse_cmd('copen 5', {})
+      eq(5, result.count)
+    end)
   end)
 
   describe('nvim_cmd', function()
@@ -5396,6 +5404,57 @@ describe('API', function()
       -- Clean up
       os.remove('Xfile')
     end)
+    it('interprets numeric args as count for count-only commands', function()
+      api.nvim_cmd({ cmd = 'copen', args = { 8 } }, {})
+      local height1 = api.nvim_win_get_height(0)
+      command('cclose')
+      api.nvim_cmd({ cmd = 'copen', count = 8 }, {})
+      local height2 = api.nvim_win_get_height(0)
+      command('cclose')
+      eq(height1, height2)
+
+      exec_lua 'vim.cmd.copen(5)'
+      height2 = api.nvim_win_get_height(0)
+      command('cclose')
+      eq(5, height2)
+
+      -- should reject both count and numeric arg
+      eq(
+        "Cannot specify both 'count' and numeric argument",
+        pcall_err(api.nvim_cmd, { cmd = 'copen', args = { 5 }, count = 10 }, {})
+      )
+    end)
+    it('handles string numeric arguments correctly', function()
+      -- Valid string numbers should work
+      api.nvim_cmd({ cmd = 'copen', args = { '6' } }, {})
+      eq(6, api.nvim_win_get_height(0))
+      command('cclose')
+      -- Invalid strings should be rejected
+      eq(
+        'Wrong number of arguments',
+        pcall_err(api.nvim_cmd, { cmd = 'copen', args = { 'abc' } }, {})
+      )
+      -- Partial numbers should be rejected
+      eq(
+        'Wrong number of arguments',
+        pcall_err(api.nvim_cmd, { cmd = 'copen', args = { '8abc' } }, {})
+      )
+      -- Empty string should be rejected
+      eq(
+        'Invalid command arg: expected non-whitespace',
+        pcall_err(api.nvim_cmd, { cmd = 'copen', args = { '' } }, {})
+      )
+      -- Negative string numbers should be rejected
+      eq(
+        'Wrong number of arguments',
+        pcall_err(api.nvim_cmd, { cmd = 'copen', args = { '-5' } }, {})
+      )
+      -- Leading/trailing spaces should be rejected
+      eq(
+        'Wrong number of arguments',
+        pcall_err(api.nvim_cmd, { cmd = 'copen', args = { ' 5 ' } }, {})
+      )
+    end)
   end)
 
   it('nvim__redraw', function()