add attribute try_from

test_suite/tests/ui/conflict/from-try-from.rs

@@ -0,0 +1,9 @@
+use serde_derive::Serialize;
+
+#[derive(Serialize)]
+#[serde(from = "u64", try_from = "u64")]
+struct S {
+    a: u8,
+}
+
+fn main() {}

test_suite/tests/ui/conflict/from-try-from.stderr

@@ -0,0 +1,8 @@
+error: #[serde(from = "...")] and #[serde(try_from = "...")] conflict with each other
+ --> $DIR/from-try-from.rs:4:1
+  |
+4 | / #[serde(from = "u64", try_from = "u64")]
+5 | | struct S {
+6 | |     a: u8,
+7 | | }
+  | |_^