From 35f53016759e7221237550a9bdce3342344f63a0 Mon Sep 17 00:00:00 2001
From: kngwyu <yuji.kngw.80s.revive@gmail.com>
Date: Tue, 4 Jun 2019 14:17:07 +0900
Subject: [PATCH] Reject generics explicitly for #[pyclass]

---
 Cargo.toml                         |  1 +
 pyo3-derive-backend/src/pyclass.rs | 12 ++++++++++++
 tests/test_compile_error.rs        |  6 ++++++
 tests/ui/reject_generics.rs        |  8 ++++++++
 tests/ui/reject_generics.stderr    |  5 +++++
 5 files changed, 32 insertions(+)
 create mode 100644 tests/test_compile_error.rs
 create mode 100644 tests/ui/reject_generics.rs
 create mode 100644 tests/ui/reject_generics.stderr

diff --git a/Cargo.toml b/Cargo.toml
index 8330905d..fbdf69b7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,6 +30,7 @@ inventory = "0.1.3"
 [dev-dependencies]
 assert_approx_eq = "1.1.0"
 indoc = "0.3.3"
+trybuild = "1.0"
 
 [build-dependencies]
 regex = "1.1.6"
diff --git a/pyo3-derive-backend/src/pyclass.rs b/pyo3-derive-backend/src/pyclass.rs
index 04f37868..cbd4fbfc 100644
--- a/pyo3-derive-backend/src/pyclass.rs
+++ b/pyo3-derive-backend/src/pyclass.rs
@@ -154,6 +154,7 @@ pub fn build_py_class(class: &mut syn::ItemStruct, attr: &PyClassArgs) -> syn::R
     let doc = utils::get_doc(&class.attrs, true);
     let mut descriptors = Vec::new();
 
+    check_generics(class)?;
     if let syn::Fields::Named(ref mut fields) = class.fields {
         for field in fields.named.iter_mut() {
             let field_descs = parse_descriptors(field)?;
@@ -461,3 +462,14 @@ fn impl_descriptors(cls: &syn::Type, descriptors: Vec<(syn::Field, Vec<FnType>)>
         }
     }
 }
+
+fn check_generics(class: &mut syn::ItemStruct) -> syn::Result<()> {
+    if class.generics.params.is_empty() {
+        Ok(())
+    } else {
+        Err(syn::Error::new_spanned(
+            &class.generics,
+            "#[pyclass] cannot have generic parameters",
+        ))
+    }
+}
diff --git a/tests/test_compile_error.rs b/tests/test_compile_error.rs
new file mode 100644
index 00000000..0437d5e3
--- /dev/null
+++ b/tests/test_compile_error.rs
@@ -0,0 +1,6 @@
+#[test]
+#[cfg(testkcovstopmarker)]
+fn test_compile_errors() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/reject_generics.rs");
+}
diff --git a/tests/ui/reject_generics.rs b/tests/ui/reject_generics.rs
new file mode 100644
index 00000000..b400cd2b
--- /dev/null
+++ b/tests/ui/reject_generics.rs
@@ -0,0 +1,8 @@
+use pyo3::prelude::*;
+
+#[pyclass]
+struct ClassWithGenerics<A> {
+    a: A,
+}
+
+fn main() {}
diff --git a/tests/ui/reject_generics.stderr b/tests/ui/reject_generics.stderr
new file mode 100644
index 00000000..c06f9dfb
--- /dev/null
+++ b/tests/ui/reject_generics.stderr
@@ -0,0 +1,5 @@
+error: #[pyclass] cannot have generic parameters
+ --> $DIR/reject_generics.rs:4:25
+  |
+4 | struct ClassWithGenerics<A> {
+  |                         ^^^