From d339cd0dc9c65da76ab8ed8b76ebbbbae72165c9 Mon Sep 17 00:00:00 2001
From: b05902132 <b05902132@csie.ntu.edu.tw>
Date: Tue, 23 Nov 2021 00:58:33 +0800
Subject: [PATCH] Let #[pyclass] reject empty enums.

---
 pyo3-macros-backend/src/pyclass.rs   | 3 +++
 tests/ui/invalid_pyclass_enum.rs     | 3 +++
 tests/ui/invalid_pyclass_enum.stderr | 6 ++++++
 3 files changed, 12 insertions(+)

diff --git a/pyo3-macros-backend/src/pyclass.rs b/pyo3-macros-backend/src/pyclass.rs
index 3e59a960..52f7c319 100644
--- a/pyo3-macros-backend/src/pyclass.rs
+++ b/pyo3-macros-backend/src/pyclass.rs
@@ -386,6 +386,9 @@ pub fn build_py_enum(
     args: PyClassArgs,
     method_type: PyClassMethodsType,
 ) -> syn::Result<TokenStream> {
+    if enum_.variants.is_empty() {
+        bail_spanned!(enum_.brace_token.span => "Empty enums can't be #[pyclass].");
+    }
     let variants: Vec<PyClassEnumVariant> = enum_
         .variants
         .iter()
diff --git a/tests/ui/invalid_pyclass_enum.rs b/tests/ui/invalid_pyclass_enum.rs
index 62f2a3d6..a12accbf 100644
--- a/tests/ui/invalid_pyclass_enum.rs
+++ b/tests/ui/invalid_pyclass_enum.rs
@@ -12,4 +12,7 @@ enum NotDrivedClass {
     y,
 }
 
+#[pyclass]
+enum NoEmptyEnum {}
+
 fn main() {}
diff --git a/tests/ui/invalid_pyclass_enum.stderr b/tests/ui/invalid_pyclass_enum.stderr
index 2dd0e737..eea36e5c 100644
--- a/tests/ui/invalid_pyclass_enum.stderr
+++ b/tests/ui/invalid_pyclass_enum.stderr
@@ -9,3 +9,9 @@ error: enums cannot extend from other classes
   |
 9 | #[pyclass(extends = PyList)]
   |           ^^^^^^^
+
+error: Empty enums can't be #[pyclass].
+  --> tests/ui/invalid_pyclass_enum.rs:16:18
+   |
+16 | enum NoEmptyEnum {}
+   |                  ^^