ex_cmds: port :eval

Cherry-picked from patch v8.1.1807.
Required for patch v8.2.2761.

runtime/doc/eval.txt

@@ -10099,6 +10099,8 @@ This function can then be called with: >
 The recursiveness of user functions is restricted with the |'maxfuncdepth'|
 option.
 
+It is also possible to use `:eval`.  It does not support a range.
+
 
 AUTOMATICALLY LOADING FUNCTIONS ~
 							*autoload-functions*
@@ -10532,6 +10534,20 @@ text...
 			Unlock the internal variable {name}.  Does the
 			opposite of |:lockvar|.
 
+                                                       *:eval*
+:eval {expr}           Evaluate {expr} and discard the result.  Example: >
+                               :eval append(Filter(Getlist()), '$')
+
+<                      The expression is supposed to have a side effect,
+                       since the resulting value is not used.  In the example
+                       the `append()` call appends the List with text to the
+                       buffer.  This is similar to `:call` but works with any
+                       expression.
+
+                       The command can be shortened to `:ev` or `:eva`, but
+                       these are hard to recognize and therefore not to be
+                       used.
+
 
 :if {expr1}			*:if* *:end* *:endif* *:en* *E171* *E579* *E580*
 :en[dif]		Execute the commands until the next matching ":else"

src/nvim/ex_cmds.lua

@@ -927,6 +927,12 @@ module.cmds = {
     addr_type='ADDR_NONE',
     func='ex_edit',
   },
+  {
+    command='eval',
+    flags=bit.bor(EXTRA, NOTRLCOM, SBOXOK, CMDWIN),
+    addr_type='ADDR_NONE',
+    func='ex_eval',
+  },
   {
     command='ex',
     flags=bit.bor(BANG, FILE1, CMDARG, ARGOPT, TRLBAR),

src/nvim/ex_eval.c

@@ -788,6 +788,15 @@ void report_discard_pending(int pending, void *value)
   }
 }
 
+// ":eval".
+void ex_eval(exarg_T *eap)
+{
+  typval_T tv;
+
+  if (eval0(eap->arg, &tv, &eap->nextcmd, !eap->skip) == OK) {
+    tv_clear(&tv);
+  }
+}
 
 /*
  * ":if".