fix(api): nvim_parse_cmd parses :map incorrectly #34068

Problem: nvim_parse_cmd() incorrectly splits mapping commands like
into three arguments instead of preserving whitespace in the RHS.

Solution: Add special handling for mapping commands to parse them as exactly
two arguments - the LHS and the RHS with all whitespace preserved.

src/nvim/api/command.c

@@ -15,6 +15,7 @@
 #include "nvim/autocmd.h"
 #include "nvim/autocmd_defs.h"
 #include "nvim/buffer_defs.h"
+#include "nvim/charset.h"
 #include "nvim/cmdexpand_defs.h"
 #include "nvim/ex_cmds_defs.h"
 #include "nvim/ex_docmd.h"
@@ -40,6 +41,31 @@
 # include "api/command.c.generated.h"
 #endif
 
+/// Parse arguments for :map/:abbrev commands, preserving whitespace in RHS.
+/// @param arg_str  The argument string to parse
+/// @param arena    Arena allocator
+/// @return Array with at most 2 elements: [lhs, rhs]
+static Array parse_map_cmd(const char *arg_str, Arena *arena)
+{
+  Array args = arena_array(arena, 2);
+
+  char *lhs_start = (char *)arg_str;
+  char *lhs_end = skiptowhite(lhs_start);
+  size_t lhs_len = (size_t)(lhs_end - lhs_start);
+
+  // Add the LHS (first argument)
+  ADD_C(args, STRING_OBJ(cstrn_as_string(lhs_start, lhs_len)));
+
+  // Add the RHS (second argument) if it exists, preserving all whitespace
+  char *rhs_start = skipwhite(lhs_end);
+  if (*rhs_start != NUL) {
+    size_t rhs_len = strlen(rhs_start);
+    ADD_C(args, STRING_OBJ(cstrn_as_string(rhs_start, rhs_len)));
+  }
+
+  return args;
+}
+
 /// Parse command line.
 ///
 /// Doesn't check the validity of command arguments.
@@ -121,9 +147,15 @@ Dict(cmd) nvim_parse_cmd(String str, Dict(empty) *opts, Arena *arena, Error *err
   Array args = ARRAY_DICT_INIT;
   size_t length = strlen(ea.arg);
 
+  // Check if this is a mapping command that needs special handling
+  // like mapping commands need special argument parsing to preserve whitespace in RHS:
+  // "map a b  c" => { args=["a", "b  c"], ... }
+  if (is_map_cmd(ea.cmdidx) && *ea.arg != NUL) {
+    // For mapping commands, split differently to preserve whitespace
+    args = parse_map_cmd(ea.arg, arena);
+  } else if (ea.argt & EX_NOSPC) {
     // For nargs = 1 or '?', pass the entire argument list as a single argument,
     // otherwise split arguments by whitespace.
-  if (ea.argt & EX_NOSPC) {
     if (*ea.arg != NUL) {
       args = arena_array(arena, 1);
       ADD_C(args, STRING_OBJ(cstrn_as_string(ea.arg, length)));

src/nvim/ex_docmd.c

@@ -8187,3 +8187,18 @@ uint32_t get_cmd_argt(cmdidx_T cmdidx)
 {
   return cmdnames[(int)cmdidx].cmd_argt;
 }
+
+/// Check if a command is a :map/:abbrev command.
+bool is_map_cmd(cmdidx_T cmdidx)
+{
+  if (IS_USER_CMDIDX(cmdidx)) {
+    return false;
+  }
+
+  ex_func_T func = cmdnames[cmdidx].cmd_func;
+  return func == ex_map           // :map, :nmap, :noremap, etc.
+         || func == ex_unmap         // :unmap, :nunmap, etc.
+         || func == ex_mapclear      // :mapclear, :nmapclear, etc.
+         || func == ex_abbreviate    // :abbreviate, :iabbrev, etc.
+         || func == ex_abclear;      // :abclear, :iabclear, etc.
+}

test/functional/api/vim_spec.lua

@@ -4641,6 +4641,45 @@ describe('API', function()
         },
       }, api.nvim_parse_cmd('argadd a.txt | argadd b.txt', {}))
     end)
+    it('parses :map commands with space in RHS', function()
+      eq({
+        addr = 'none',
+        args = { 'a', 'b  c' },
+        bang = false,
+        cmd = 'map',
+        magic = {
+          bar = true,
+          file = false,
+        },
+        mods = {
+          browse = false,
+          confirm = false,
+          emsg_silent = false,
+          filter = {
+            force = false,
+            pattern = '',
+          },
+          hide = false,
+          horizontal = false,
+          keepalt = false,
+          keepjumps = false,
+          keepmarks = false,
+          keeppatterns = false,
+          lockmarks = false,
+          noautocmd = false,
+          noswapfile = false,
+          sandbox = false,
+          silent = false,
+          split = '',
+          tab = -1,
+          unsilent = false,
+          verbose = -1,
+          vertical = false,
+        },
+        nargs = '*',
+        nextcmd = '',
+      }, api.nvim_parse_cmd('map a b  c', {}))
+    end)
     it('works for nargs=1', function()
       command('command -nargs=1 MyCommand echo <q-args>')
       eq({