vim-patch:8.2.0817: not enough memory allocated when converting string

Problem:    Not enough memory allocated when converting string with special
            character.
Solution:   Reserve space for modifier code. (closes vim/vim#6130)
f7271e8316

Cherry-pick Test_eval(), Test_nr2char() from patch 8.2.0448.

src/nvim/eval.c

@@ -4518,7 +4518,6 @@ int get_option_tv(const char **const arg, typval_T *const rettv,
 static int get_string_tv(char_u **arg, typval_T *rettv, int evaluate)
 {
   char_u      *p;
-  char_u      *name;
   unsigned int extra = 0;
 
   /*
@@ -4526,11 +4525,13 @@ static int get_string_tv(char_u **arg, typval_T *rettv, int evaluate)
    */
   for (p = *arg + 1; *p != NUL && *p != '"'; MB_PTR_ADV(p)) {
     if (*p == '\\' && p[1] != NUL) {
-      ++p;
+      p++;
-      /* A "\<x>" form occupies at least 4 characters, and produces up
+      // A "\<x>" form occupies at least 4 characters, and produces up
-       * to 6 characters: reserve space for 2 extra */
+      // to 9 characters (6 for the char and 3 for a modifier): reserve
-      if (*p == '<')
+      // space for 5 extra.
-        extra += 2;
+      if (*p == '<') {
+        extra += 5;
+      }
     }
   }
 
@@ -4549,7 +4550,8 @@ static int get_string_tv(char_u **arg, typval_T *rettv, int evaluate)
    * Copy the string into allocated memory, handling backslashed
    * characters.
    */
-  name = xmalloc(p - *arg + extra);
+  const int len = (int)(p - *arg + extra);
+  char_u *name = xmalloc(len);
   rettv->v_type = VAR_STRING;
   rettv->vval.v_string = name;
 
@@ -4616,6 +4618,9 @@ static int get_string_tv(char_u **arg, typval_T *rettv, int evaluate)
         extra = trans_special((const char_u **)&p, STRLEN(p), name, true, true);
         if (extra != 0) {
           name += extra;
+          if (name >= rettv->vval.v_string + len) {
+            iemsg("get_string_tv() used more space than allocated");
+          }
           break;
         }
         FALLTHROUGH;

src/nvim/testdir/test_functions.vim

@@ -1359,3 +1359,21 @@ func Test_readdir()
 
   call delete('Xdir', 'rf')
 endfunc
+
+" Test for the eval() function
+func Test_eval()
+  call assert_fails("call eval('5 a')", 'E488:')
+endfunc
+
+" Test for the nr2char() function
+func Test_nr2char()
+  " set encoding=latin1
+  call assert_equal('@', nr2char(64))
+  set encoding=utf8
+  call assert_equal('a', nr2char(97, 1))
+  call assert_equal('a', nr2char(97, 0))
+
+  call assert_equal("\x80\xfc\b\xf4\x80\xfeX\x80\xfeX\x80\xfeX", eval('"\<M-' .. nr2char(0x100000) .. '>"'))
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab