fix(api): nvim_parse_cmd handle nextcmd for commands without EX_TRLBAR (#36055)

Problem: nvim_parse_cmd('exe "ls"|edit foo', {}) fails to separate
nextcmd, returning args as { '"ls"|edit', 'foo' } instead of { '"ls"' }
with nextcmd='edit foo'.

Solution: Skip expressions before checking for '|' separator.

src/nvim/eval.c

@@ -1986,11 +1986,7 @@ void set_context_for_expression(expand_T *xp, char *arg, cmdidx_T cmdidx)
   }
 
   // ":exe one two" completes "two"
-  if ((cmdidx == CMD_execute
-       || cmdidx == CMD_echo
-       || cmdidx == CMD_echon
-       || cmdidx == CMD_echomsg)
-      && xp->xp_context == EXPAND_EXPRESSION) {
+  if (cmd_has_expr_args(cmdidx) && xp->xp_context == EXPAND_EXPRESSION) {
     while (true) {
       char *const n = skiptowhite(arg);
 

src/nvim/ex_docmd.c

@@ -13,6 +13,7 @@
 
 #include "auto/config.h"
 #include "nvim/api/private/defs.h"
+#include "nvim/api/private/dispatch.h"
 #include "nvim/api/private/helpers.h"
 #include "nvim/api/ui.h"
 #include "nvim/api/vimscript.h"
@@ -1507,6 +1508,16 @@ static bool parse_bang(const exarg_T *eap, char **p)
   return false;
 }
 
+/// Check if command expects expression arguments that need special parsing
+bool cmd_has_expr_args(cmdidx_T cmdidx)
+{
+  return cmdidx == CMD_execute
+         || cmdidx == CMD_echo
+         || cmdidx == CMD_echon
+         || cmdidx == CMD_echomsg
+         || cmdidx == CMD_echoerr;
+}
+
 /// Parse command line and return information about the first command.
 /// If parsing is done successfully, need to free cmod_filter_pat and cmod_filter_regmatch.regprog
 /// after calling, usually done using undo_cmdmod() or execute_cmd().
@@ -1596,6 +1607,22 @@ bool parse_cmdline(char **cmdline, exarg_T *eap, CmdParseInfo *cmdinfo, const ch
   // Don't do this for ":read !cmd" and ":write !cmd".
   if ((eap->argt & EX_TRLBAR)) {
     separate_nextcmd(eap);
+  } else if (cmd_has_expr_args(eap->cmdidx)) {
+    // For commands without EX_TRLBAR, check for '|' separator
+    // by skipping over expressions (including string literals)
+    char *arg = eap->arg;
+    while (*arg != NUL && *arg != '|' && *arg != '\n') {
+      char *start = arg;
+      skip_expr(&arg, NULL);
+      // If skip_expr didn't advance, move forward to avoid infinite loop
+      if (arg == start) {
+        arg++;
+      }
+    }
+    if (*arg == '|' || *arg == '\n') {
+      eap->nextcmd = check_nextcmd(arg);
+      *arg = NUL;
+    }
   }
   // Fail if command doesn't support bang but is used with a bang
   if (!(eap->argt & EX_BANG) && eap->forceit) {

test/functional/api/vim_spec.lua

@@ -4849,6 +4849,12 @@ describe('API', function()
       result = api.nvim_parse_cmd('copen 5', {})
       eq(5, result.count)
     end)
+    it('parses nextcmd for commands #36029', function()
+      local result = api.nvim_parse_cmd('exe "ls"|edit foo', {})
+      eq({ '"ls"' }, result.args)
+      eq('execute', result.cmd)
+      eq('edit foo', result.nextcmd)
+    end)
   end)
 
   describe('nvim_cmd', function()