patch 8.2.2614: Vim9: function is deleted while executing

Problem:    Vim9: function is deleted while executing.
Solution:   increment the call count, when more than zero do not delete the
            function but mark it as dead. (closes #7977)

src/testdir/test_vim9_script.vim

@@ -1561,6 +1561,35 @@ def Test_script_reload_change_type()
   delete('Xreload.vim')
 enddef
 
+" Define CallFunc so that the test can be compiled
+command CallFunc echo 'nop'
+
+def Test_script_reload_from_function()
+  var lines =<< trim END
+      vim9script
+
+      if exists('g:loaded')
+        finish
+      endif
+      g:loaded = 1
+      delcommand CallFunc
+      command CallFunc Func()
+      def Func()
+        so /tmp/test.vim
+        g:didTheFunc = 1
+      enddef
+  END
+  writefile(lines, 'XreloadFunc.vim')
+  source XreloadFunc.vim
+  CallFunc
+  assert_equal(1, g:didTheFunc)
+
+  delete('XreloadFunc.vim')
+  delcommand CallFunc
+  unlet g:loaded
+  unlet g:didTheFunc
+enddef
+
 def Test_script_var_shadows_function()
   var lines =<< trim END
       vim9script

src/userfunc.c

@@ -1359,9 +1359,12 @@ func_remove(ufunc_T *fp)
 	// function, so we can find the index when defining the function again.
 	// Do remove it when it's a copy.
 	if (fp->uf_def_status == UF_COMPILED && (fp->uf_flags & FC_COPY) == 0)
+	{
 	    fp->uf_flags |= FC_DEAD;
-	else
-	    hash_remove(&func_hashtab, hi);
+	    return FALSE;
+	}
+	hash_remove(&func_hashtab, hi);
+	fp->uf_flags |= FC_DELETED;
 	return TRUE;
     }
     return FALSE;
@@ -2134,11 +2137,23 @@ delete_script_functions(int sid)
 		    int changed = func_hashtab.ht_changed;
 
 		    fp->uf_flags |= FC_DEAD;
-		    func_clear(fp, TRUE);
-		    // When clearing a function another function can be cleared
-		    // as a side effect.  When that happens start over.
-		    if (changed != func_hashtab.ht_changed)
-			break;
+
+		    if (fp->uf_calls > 0)
+		    {
+			// Function is executing, don't free it but do remove
+			// it from the hashtable.
+			if (func_remove(fp))
+			    fp->uf_refcount--;
+		    }
+		    else
+		    {
+			func_clear(fp, TRUE);
+			// When clearing a function another function can be
+			// cleared as a side effect.  When that happens start
+			// over.
+			if (changed != func_hashtab.ht_changed)
+			    break;
+		    }
 		}
 		--todo;
 	    }
@@ -4251,7 +4266,6 @@ ex_delfunction(exarg_T *eap)
 		// do remove it from the hashtable.
 		if (func_remove(fp))
 		    fp->uf_refcount--;
-		fp->uf_flags |= FC_DELETED;
 	    }
 	    else
 		func_clear_free(fp, FALSE);

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2614,
 /**/
     2613,
 /**/

src/vim9execute.c

@@ -323,6 +323,8 @@ call_dfunc(int cdf_idx, partial_T *pt, int argcount_arg, ectx_T *ectx)
     else
 	ectx->ec_outer = NULL;
 
+    ++ufunc->uf_calls;
+
     // Set execution state to the start of the called function.
     ectx->ec_dfunc_idx = cdf_idx;
     ectx->ec_instr = INSTRUCTIONS(dfunc);
@@ -556,6 +558,9 @@ func_return(ectx_T *ectx)
 	}
     }
 #endif
+    // TODO: when is it safe to delete the function when it is no longer used?
+    --dfunc->df_ufunc->uf_calls;
+
     // execution context goes one level up
     entry = estack_pop();
     if (entry != NULL)
@@ -1334,7 +1339,7 @@ call_def_function(
 	    ++ectx.ec_stack.ga_len;
 	}
     if (ufunc->uf_va_name != NULL)
-	    ++ectx.ec_stack.ga_len;
+	++ectx.ec_stack.ga_len;
 
     // Frame pointer points to just after arguments.
     ectx.ec_frame_idx = ectx.ec_stack.ga_len;
@@ -1407,6 +1412,9 @@ call_def_function(
     // Do turn errors into exceptions.
     suppress_errthrow = FALSE;
 
+    // Do not delete the function while executing it.
+    ++ufunc->uf_calls;
+
     // When ":silent!" was used before calling then we still abort the
     // function.  If ":silent!" is used in the function then we don't.
     emsg_silent_def = emsg_silent;
@@ -3838,6 +3846,9 @@ failed:
     estack_pop();
     current_sctx = save_current_sctx;
 
+    // TODO: when is it safe to delete the function if it is no longer used?
+    --ufunc->uf_calls;
+
     if (*msg_list != NULL && saved_msg_list != NULL)
     {
 	msglist_T **plist = saved_msg_list;