vim-patch:8.2.4359: crash when repeatedly using :retab

Problem:    crash when repeatedly using :retab.
Solution:   Bail out when the line is getting too long.
6e28703a8e

Cherry-pick e_resulting_text_too_long from v8.2.3492; put it in globals.h as
it will eventually be used in other files.

Add a modeline to test_retab.vim

src/nvim/ex_cmds.c

@@ -847,6 +847,10 @@ void ex_retab(exarg_T *eap)
         break;
       }
       vcol += win_chartabsize(curwin, ptr + col, (colnr_T)vcol);
+      if (vcol >= MAXCOL) {
+        emsg(_(e_resulting_text_too_long));
+        break;
+      }
       col += utfc_ptr2len(ptr + col);
     }
     if (new_line == NULL) {                 // out of memory

src/nvim/globals.h

@@ -1000,6 +1000,8 @@ EXTERN char e_non_empty_string_required[] INIT(= N_("E1142: Non-empty string req
 
 EXTERN char e_cannot_define_autocommands_for_all_events[] INIT(= N_("E1155: Cannot define autocommands for ALL events"));
 
+EXTERN char e_resulting_text_too_long[] INIT(= N_("E1240: Resulting text too long"));
+
 EXTERN char e_highlight_group_name_too_long[] INIT(= N_("E1249: Highlight group name too long"));
 
 EXTERN char top_bot_msg[] INIT(= N_("search hit TOP, continuing at BOTTOM"));

src/nvim/testdir/test_retab.vim

@@ -69,6 +69,8 @@ func Test_retab()
   call assert_equal("    a       b        c    ",         Retab('!', 3))
   call assert_equal("    a       b        c    ",         Retab('',  5))
   call assert_equal("    a       b        c    ",         Retab('!', 5))
+
+  set tabstop& expandtab&
 endfunc
 
 func Test_retab_error()
@@ -78,3 +80,22 @@ func Test_retab_error()
   call assert_fails('ret 10000', 'E475:')
   call assert_fails('ret 80000000000000000000', 'E475:')
 endfunc
+
+func Test_retab_endless()
+  new
+  call setline(1, "\t0\t")
+  let caught = 'no'
+  try
+    while 1
+      set ts=4000
+      retab 4
+    endwhile
+  catch /E1240/
+    let caught = 'yes'
+  endtry
+  bwipe!
+  set tabstop&
+endfunc
+
+
+" vim: shiftwidth=2 sts=2 expandtab