Upgrade syn crate to 2.0.45 version (#341, #301)

Upgrade minimal version of `syn` up to 2.0.45 version to fix the extended
enum syntax, and cover the use case with tests for future regressions.

impl/Cargo.toml

@@ -25,7 +25,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = "2.0"
+syn = "2.0.45"
 convert_case = { version = "0.6", optional = true }
 unicode-xid = { version = "0.2.2", optional = true }
 

tests/debug.rs

@@ -1914,3 +1914,21 @@ mod generic {
         }
     }
 }
+
+// See: https://github.com/JelteF/derive_more/issues/301
+mod complex_enum_syntax {
+    #[cfg(not(feature = "std"))]
+    use alloc::{boxed::Box, format};
+
+    use derive_more::Debug;
+
+    #[derive(Debug)]
+    enum Enum {
+        A = if cfg!(unix) { 2 } else { 3 },
+    }
+
+    #[test]
+    fn assert() {
+        assert_eq!(format!("{:?}", Enum::A), "A");
+    }
+}