add attribute try_from

test_suite/tests/test_annotations.rs

@@ -5,6 +5,7 @@ use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
 use std::collections::{BTreeMap, HashMap};
 use std::fmt;
+use std::convert::TryFrom;
 use std::marker::PhantomData;
 
 use serde_test::{
@@ -1588,6 +1589,25 @@ impl From<Option<u32>> for EnumToU32 {
     }
 }
 
+#[derive(Clone, Deserialize, PartialEq, Debug)]
+#[serde(try_from = "EnumToU32")]
+struct StructTryFromEnum(Option<u32>);
+
+impl TryFrom<EnumToU32> for StructTryFromEnum {
+    type Error = String;
+
+    fn try_from(value: EnumToU32) -> Result<Self, Self::Error> {
+        println!("{:?}", value);
+        match value {
+            EnumToU32::One => Ok(StructTryFromEnum(Some(1))),
+            EnumToU32::Two => Ok(StructTryFromEnum(Some(2))),
+            EnumToU32::Three => Ok(StructTryFromEnum(Some(3))),
+            EnumToU32::Four => Ok(StructTryFromEnum(Some(4))),
+            _ => Err("out of range".into()),
+        }
+    }
+}
+
 #[test]
 fn test_from_into_traits() {
     assert_ser_tokens::<EnumToU32>(&EnumToU32::One, &[Token::Some, Token::U32(1)]);
@@ -1596,6 +1616,9 @@ fn test_from_into_traits() {
     assert_ser_tokens::<StructFromEnum>(&StructFromEnum(Some(5)), &[Token::None]);
     assert_ser_tokens::<StructFromEnum>(&StructFromEnum(None), &[Token::None]);
     assert_de_tokens::<StructFromEnum>(&StructFromEnum(Some(2)), &[Token::Some, Token::U32(2)]);
+    assert_de_tokens::<StructTryFromEnum>(&StructTryFromEnum(Some(2)), &[Token::Some, Token::U32(2)]);
+    assert_de_tokens_error::<StructTryFromEnum>(&[Token::Some, Token::U32(5)], "out of range");
+    assert_de_tokens_error::<StructTryFromEnum>(&[Token::None], "out of range");
 }
 
 #[test]

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 | | }
+  | |_^

test_suite/tests/ui/transparent/with_try_from.rs

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

test_suite/tests/ui/transparent/with_try_from.stderr

@@ -0,0 +1,8 @@
+error: #[serde(transparent)] is not allowed with #[serde(try_from = "...")]
+ --> $DIR/with_try_from.rs:4:1
+  |
+4 | / #[serde(transparent, try_from = "u64")]
+5 | | struct S {
+6 | |     a: u8,
+7 | | }
+  | |_^

test_suite/tests/ui/type-attribute/try_from.rs

@@ -0,0 +1,12 @@
+use serde_derive::Deserialize;
+
+#[derive(Deserialize)]
+#[serde(try_from = "Option<T")]
+enum TestOne {
+    Testing,
+    One,
+    Two,
+    Three,
+}
+
+fn main() {}

test_suite/tests/ui/type-attribute/try_from.stderr

@@ -0,0 +1,5 @@
+error: failed to parse type: try_from = "Option<T"
+ --> $DIR/try_from.rs:4:20
+  |
+4 | #[serde(try_from = "Option<T")]
+  |                    ^^^^^^^^^^