1 files changed, 161 insertions, 0 deletions
diff --git a/tests/test_generics.rs b/tests/test_generics.rs
new file mode 100644
index 0000000..f5e1de2
--- /dev/null
+++ b/tests/test_generics.rs
@@ -0,0 +1,161 @@
+#![deny(clippy::all, clippy::pedantic)]
+
+use std::fmt::{self, Debug, Display};
+use thiserror::Error;
+
+pub struct NoFormat;
+
+#[derive(Debug)]
+pub struct DebugOnly;
+
+pub struct DisplayOnly;
+
+impl Display for DisplayOnly {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("display only")
+    }
+}
+
+#[derive(Debug)]
+pub struct DebugAndDisplay;
+
+impl Display for DebugAndDisplay {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("debug and display")
+    }
+}
+
+// Should expand to:
+//
+//     impl<E> Display for EnumDebugField<E>
+//     where
+//         E: Debug;
+//
+//     impl<E> Error for EnumDebugField<E>
+//     where
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+pub enum EnumDebugGeneric<E> {
+    #[error("{0:?}")]
+    FatalError(E),
+}
+
+// Should expand to:
+//
+//     impl<E> Display for EnumFromGeneric<E>;
+//
+//     impl<E> Error for EnumFromGeneric<E>
+//     where
+//         EnumDebugGeneric<E>: Error + 'static,
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+pub enum EnumFromGeneric<E> {
+    #[error("enum from generic")]
+    Source(#[from] EnumDebugGeneric<E>),
+}
+
+// Should expand to:
+//
+//     impl<HasDisplay, HasDebug, HasNeither> Display
+//         for EnumCompound<HasDisplay, HasDebug, HasNeither>
+//     where
+//         HasDisplay: Display,
+//         HasDebug: Debug;
+//
+//     impl<HasDisplay, HasDebug, HasNeither> Error
+//         for EnumCompound<HasDisplay, HasDebug, HasNeither>
+//     where
+//         Self: Debug + Display;
+//
+#[derive(Error)]
+pub enum EnumCompound<HasDisplay, HasDebug, HasNeither> {
+    #[error("{0} {1:?}")]
+    DisplayDebug(HasDisplay, HasDebug),
+    #[error("{0}")]
+    Display(HasDisplay, HasNeither),
+    #[error("{1:?}")]
+    Debug(HasNeither, HasDebug),
+}
+
+impl<HasDisplay, HasDebug, HasNeither> Debug for EnumCompound<HasDisplay, HasDebug, HasNeither> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("EnumCompound")
+    }
+}
+
+#[test]
+fn test_display_enum_compound() {
+    let mut instance: EnumCompound<DisplayOnly, DebugOnly, NoFormat>;
+
+    instance = EnumCompound::DisplayDebug(DisplayOnly, DebugOnly);
+    assert_eq!(format!("{}", instance), "display only DebugOnly");
+
+    instance = EnumCompound::Display(DisplayOnly, NoFormat);
+    assert_eq!(format!("{}", instance), "display only");
+
+    instance = EnumCompound::Debug(NoFormat, DebugOnly);
+    assert_eq!(format!("{}", instance), "DebugOnly");
+}
+
+// Should expand to:
+//
+//     impl<E> Display for EnumTransparentGeneric<E>
+//     where
+//         E: Display;
+//
+//     impl<E> Error for EnumTransparentGeneric<E>
+//     where
+//         E: Error,
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+pub enum EnumTransparentGeneric<E> {
+    #[error(transparent)]
+    Other(E),
+}
+
+// Should expand to:
+//
+//     impl<E> Display for StructDebugGeneric<E>
+//     where
+//         E: Debug;
+//
+//     impl<E> Error for StructDebugGeneric<E>
+//     where
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+#[error("{underlying:?}")]
+pub struct StructDebugGeneric<E> {
+    pub underlying: E,
+}
+
+// Should expand to:
+//
+//     impl<E> Error for StructFromGeneric<E>
+//     where
+//         StructDebugGeneric<E>: Error + 'static,
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+pub struct StructFromGeneric<E> {
+    #[from]
+    pub source: StructDebugGeneric<E>,
+}
+
+// Should expand to:
+//
+//     impl<E> Display for StructTransparentGeneric<E>
+//     where
+//         E: Display;
+//
+//     impl<E> Error for StructTransparentGeneric<E>
+//     where
+//         E: Error,
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+#[error(transparent)]
+pub struct StructTransparentGeneric<E>(E);