vim-patch:8.2.0507: getbufvar() may get the wrong dictionary

Problem:    Getbufvar() may get the wrong dictionary. (David le Blanc)
Solution:   Check for empty name. (closes vim/vim#5878)
5259275347

src/nvim/eval.c

@@ -9536,7 +9536,8 @@ dictitem_T *find_var(const char *const name, const size_t name_len,
   return find_var_in_scoped_ht(name, name_len, no_autoload || htp != NULL);
 }
 
-/// Find variable in hashtab
+/// Find variable in hashtab.
+/// When "varname" is empty returns curwin/curtab/etc vars dictionary.
 ///
 /// @param[in]  ht  Hashtab to find variable in.
 /// @param[in]  htname  Hashtab name (first character).

src/nvim/eval/funcs.c

@@ -2831,7 +2831,9 @@ static void f_getbufvar(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     } else {
       // Look up the variable.
       // Let getbufvar({nr}, "") return the "b:" dictionary.
-      dictitem_T *const v = find_var_in_ht(&buf->b_vars->dv_hashtab, 'b',
+      dictitem_T *const v = *varname == NUL
+        ? (dictitem_T *)&buf->b_bufvar
+        : find_var_in_ht(&buf->b_vars->dv_hashtab, 'b',
                          varname, strlen(varname), false);
       if (v != NULL) {
         tv_copy(&v->di_tv, rettv);

src/nvim/testdir/test_functions.vim

@@ -666,6 +666,16 @@ func Test_getbufvar()
   call assert_equal('iso-8859-2', getbufvar(bufnr('%'), '&fenc'))
   close
 
+  " Get the b: dict.
+  let b:testvar = 'one'
+  new
+  let b:testvar = 'two'
+  let thebuf = bufnr()
+  wincmd w
+  call assert_equal('two', getbufvar(thebuf, 'testvar'))
+  call assert_equal('two', getbufvar(thebuf, '').testvar)
+  bwipe!
+
   set fileformats&
 endfunc