vim-patch:8.2.2764: memory leak when default function argument is allocated

Problem:    Memory leak when default function argument is allocated.
Solution:   Free the expression result.
b47bed2f7a

src/nvim/eval/userfunc.c

@@ -833,6 +833,8 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars,
   bool islambda = false;
   char_u numbuf[NUMBUFLEN];
   char_u      *name;
+  typval_T *tv_to_free[MAX_FUNC_ARGS];
+  int tv_to_free_len = 0;
   proftime_T wait_start;
   proftime_T call_start;
   int started_profiling = false;
@@ -985,6 +987,11 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars,
     v->di_tv = isdefault ? def_rettv : argvars[i];
     v->di_tv.v_lock = VAR_FIXED;
 
+    if (isdefault) {
+      // Need to free this later, no matter where it's stored.
+      tv_to_free[tv_to_free_len++] = &v->di_tv;
+    }
+
     if (addlocal) {
       // Named arguments can be accessed without the "a:" prefix in lambda
       // expressions. Add to the l: dict.
@@ -1209,7 +1216,9 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars,
 
   did_emsg |= save_did_emsg;
   depth--;
-
+  for (int i = 0; i < tv_to_free_len; i++) {
+    tv_clear(tv_to_free[i]);
+  }
   cleanup_function_call(fc);
 
   if (--fp->uf_calls <= 0 && fp->uf_refcount <= 0) {

src/nvim/testdir/test_functions.vim

@@ -1071,10 +1071,10 @@ func Test_inputlist()
 endfunc
 
 func Test_balloon_show()
-  if has('balloon_eval')
-    " This won't do anything but must not crash either.
-    call balloon_show('hi!')
-  endif
+  CheckFeature balloon_eval
+
+  " This won't do anything but must not crash either.
+  call balloon_show('hi!')
 endfunc
 
 func Test_shellescape()
@@ -1448,4 +1448,12 @@ func Test_nr2char()
   call assert_equal("\x80\xfc\b\xfd\x80\xfeX\x80\xfeX\x80\xfeX\x80\xfeX\x80\xfeX", eval('"\<M-' .. nr2char(0x40000000) .. '>"'))
 endfunc
 
+func HasDefault(msg = 'msg')
+  return a:msg
+endfunc
+
+func Test_default_arg_value()
+  call assert_equal('msg', HasDefault())
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab