From 3dae44db7328072d0d11936e0d4f618747cd2374 Mon Sep 17 00:00:00 2001
From: zakuro <z@kuro.red>
Date: Tue, 5 Jan 2021 09:46:32 +0900
Subject: [PATCH] checker: do not allow empty enums (#7848)

---
 vlib/v/checker/checker.v            | 3 +++
 vlib/v/checker/tests/enum_empty.out | 3 +++
 vlib/v/checker/tests/enum_empty.vv  | 1 +
 3 files changed, 7 insertions(+)
 create mode 100644 vlib/v/checker/tests/enum_empty.out
 create mode 100644 vlib/v/checker/tests/enum_empty.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 9f8a2f21da..8b42e8e484 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2194,6 +2194,9 @@ pub fn (mut c Checker) const_decl(mut node ast.ConstDecl) {
 pub fn (mut c Checker) enum_decl(decl ast.EnumDecl) {
 	c.check_valid_pascal_case(decl.name, 'enum name', decl.pos)
 	mut seen := []i64{}
+	if decl.fields.len == 0 {
+		c.error('enum cannot be empty', decl.pos)
+	}
 	for i, field in decl.fields {
 		if !c.pref.experimental && util.contains_capital(field.name) {
 			// TODO C2V uses hundreds of enums with capitals, remove -experimental check once it's handled
diff --git a/vlib/v/checker/tests/enum_empty.out b/vlib/v/checker/tests/enum_empty.out
new file mode 100644
index 0000000000..b2b432dcff
--- /dev/null
+++ b/vlib/v/checker/tests/enum_empty.out
@@ -0,0 +1,3 @@
+vlib/v/checker/tests/enum_empty.vv:1:1: error: enum cannot be empty
+    1 | enum Empty {}
+      | ~~~~~~~~~~
diff --git a/vlib/v/checker/tests/enum_empty.vv b/vlib/v/checker/tests/enum_empty.vv
new file mode 100644
index 0000000000..7afdbc006a
--- /dev/null
+++ b/vlib/v/checker/tests/enum_empty.vv
@@ -0,0 +1 @@
+enum Empty {}