vim-patch:8.2.4975: recursive command line loop may cause a crash (#18614)

Problem:    Recursive command line loop may cause a crash.
Solution:   Limit recursion of getcmdline().
51f0bfb88a

Cherry-pick e_command_too_recursive from patch 8.2.3957.

src/nvim/ex_docmd.c

@@ -345,7 +345,7 @@ int do_cmdline(char *cmdline, LineGetter fgetline, void *cookie, int flags)
   // here.  The value of 200 allows nested function calls, ":source", etc.
   // Allow 200 or 'maxfuncdepth', whatever is larger.
   if (call_depth >= 200 && call_depth >= p_mfd) {
-    emsg(_("E169: Command too recursive"));
+    emsg(_(e_command_too_recursive));
     // When converting to an exception, we do not include the command name
     // since this is not an error of the specific command.
     do_errthrow((cstack_T *)NULL, NULL);

src/nvim/ex_getln.c

@@ -804,6 +804,12 @@ static uint8_t *command_line_enter(int firstc, long count, int indent, bool init
     ccline.cmdlen = s->indent;
   }
 
+  if (cmdline_level == 50) {
+    // Somehow got into a loop recursively calling getcmdline(), bail out.
+    emsg(_(e_command_too_recursive));
+    goto theend;
+  }
+
   ExpandInit(&s->xpc);
   ccline.xpc = &s->xpc;
 
@@ -995,12 +1001,13 @@ static uint8_t *command_line_enter(int firstc, long count, int indent, bool init
   State = s->save_State;
   setmouse();
   ui_cursor_shape();            // may show different cursor shape
+  sb_text_end_cmdline();
+
+theend:
   xfree(s->save_p_icm);
   xfree(ccline.last_colors.cmdbuff);
   kv_destroy(ccline.last_colors.colors);
 
-  sb_text_end_cmdline();
-
   char_u *p = ccline.cmdbuff;
 
   if (ui_has(kUICmdline)) {

src/nvim/globals.h

@@ -878,6 +878,7 @@ EXTERN char e_argreq[] INIT(= N_("E471: Argument required"));
 EXTERN char e_backslash[] INIT(= N_("E10: \\ should be followed by /, ? or &"));
 EXTERN char e_cmdwin[] INIT(= N_("E11: Invalid in command-line window; <CR> executes, CTRL-C quits"));
 EXTERN char e_curdir[] INIT(= N_("E12: Command not allowed from exrc/vimrc in current dir or tag search"));
+EXTERN char e_command_too_recursive[] INIT(= N_("E169: Command too recursive"));
 EXTERN char e_endif[] INIT(= N_("E171: Missing :endif"));
 EXTERN char e_endtry[] INIT(= N_("E600: Missing :endtry"));
 EXTERN char e_endwhile[] INIT(= N_("E170: Missing :endwhile"));

src/nvim/testdir/test_cmdline.vim

@@ -1224,4 +1224,16 @@ func Test_screenpos_and_completion()
   call feedkeys(":let a\<C-R>=Check_completion()\<CR>\<Esc>", "xt")
 endfunc
 
+func Test_recursive_register()
+  let @= = ''
+  silent! ?e/
+  let caught = 'no'
+  try
+    normal // 
+  catch /E169:/
+    let caught = 'yes'
+  endtry
+  call assert_equal('yes', caught)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab