add attribute try_from

serde/src/export.rs

@@ -1,5 +1,5 @@
 pub use lib::clone::Clone;
-pub use lib::convert::{From, Into};
+pub use lib::convert::{From, Into, TryFrom};
 pub use lib::default::Default;
 pub use lib::fmt::{self, Formatter};
 pub use lib::marker::PhantomData;

serde_derive/src/de.rs

@@ -269,6 +269,8 @@ fn deserialize_body(cont: &Container, params: &Parameters) -> Fragment {
         deserialize_transparent(cont, params)
     } else if let Some(type_from) = cont.attrs.type_from() {
         deserialize_from(type_from)
+    } else if let Some(type_try_from) = cont.attrs.type_try_from() {
+        deserialize_try_from(type_try_from)
     } else if let attr::Identifier::No = cont.attrs.identifier() {
         match cont.data {
             Data::Enum(ref variants) => deserialize_enum(params, variants, &cont.attrs),
@@ -298,6 +300,7 @@ fn deserialize_in_place_body(cont: &Container, params: &Parameters) -> Option<St
 
     if cont.attrs.transparent()
         || cont.attrs.type_from().is_some()
+        || cont.attrs.type_try_from().is_some()
         || cont.attrs.identifier().is_some()
         || cont
             .data
@@ -390,6 +393,14 @@ fn deserialize_from(type_from: &syn::Type) -> Fragment {
     }
 }
 
+fn deserialize_try_from(type_try_from: &syn::Type) -> Fragment {
+    quote_block! {
+        _serde::export::Result::and_then(
+            <#type_try_from as _serde::Deserialize>::deserialize(__deserializer),
+            |v| _serde::export::TryFrom::try_from(v).map_err(_serde::de::Error::custom))
+    }
+}
+
 fn deserialize_unit_struct(params: &Parameters, cattrs: &attr::Container) -> Fragment {
     let this = &params.this;
     let type_name = cattrs.name().deserialize_name();

serde_derive/src/internals/attr.rs

@@ -215,6 +215,7 @@ pub struct Container {
     de_bound: Option<Vec<syn::WherePredicate>>,
     tag: TagType,
     type_from: Option<syn::Type>,
+    type_try_from: Option<syn::Type>,
     type_into: Option<syn::Type>,
     remote: Option<syn::Path>,
     identifier: Identifier,
@@ -296,6 +297,7 @@ impl Container {
         let mut internal_tag = Attr::none(cx, "tag");
         let mut content = Attr::none(cx, "content");
         let mut type_from = Attr::none(cx, "from");
+        let mut type_try_from = Attr::none(cx, "try_from");
         let mut type_into = Attr::none(cx, "into");
         let mut remote = Attr::none(cx, "remote");
         let mut field_identifier = BoolAttr::none(cx, "field_identifier");
@@ -557,6 +559,13 @@ impl Container {
                         }
                     }
 
+                    // Parse `#[serde(try_from = "Type")]
+                    Meta(NameValue(ref m)) if m.ident == "try_from" => {
+                        if let Ok(try_from_ty) = parse_lit_into_ty(cx, &m.ident, &m.lit) {
+                            type_try_from.set_opt(&m.ident, Some(try_from_ty));
+                        }
+                    }
+
                     // Parse `#[serde(into = "Type")]
                     Meta(NameValue(ref m)) if m.ident == "into" => {
                         if let Ok(into_ty) = parse_lit_into_ty(cx, &m.ident, &m.lit) {
@@ -619,6 +628,7 @@ impl Container {
             de_bound: de_bound.get(),
             tag: decide_tag(cx, item, untagged, internal_tag, content),
             type_from: type_from.get(),
+            type_try_from: type_try_from.get(),
             type_into: type_into.get(),
             remote: remote.get(),
             identifier: decide_identifier(cx, item, field_identifier, variant_identifier),
@@ -663,6 +673,10 @@ impl Container {
         self.type_from.as_ref()
     }
 
+    pub fn type_try_from(&self) -> Option<&syn::Type> {
+        self.type_try_from.as_ref()
+    }
+
     pub fn type_into(&self) -> Option<&syn::Type> {
         self.type_into.as_ref()
     }

serde_derive/src/internals/check.rs

@@ -13,6 +13,7 @@ pub fn check(cx: &Ctxt, cont: &mut Container, derive: Derive) {
     check_internal_tag_field_name_conflict(cx, cont);
     check_adjacent_tag_conflict(cx, cont);
     check_transparent(cx, cont, derive);
+    check_from_and_try_from(cx, cont);
 }
 
 /// Getters are only allowed inside structs (not enums) with the `remote`
@@ -330,6 +331,13 @@ fn check_transparent(cx: &Ctxt, cont: &mut Container, derive: Derive) {
         );
     }
 
+    if cont.attrs.type_try_from().is_some() {
+        cx.error_spanned_by(
+            cont.original,
+            "#[serde(transparent)] is not allowed with #[serde(try_from = \"...\")]",
+        );
+    }
+
     if cont.attrs.type_into().is_some() {
         cx.error_spanned_by(
             cont.original,
@@ -410,3 +418,12 @@ fn allow_transparent(field: &Field, derive: Derive) -> bool {
         Derive::Deserialize => !field.attrs.skip_deserializing() && field.attrs.default().is_none(),
     }
 }
+
+fn check_from_and_try_from(cx: &Ctxt, cont: &mut Container) {
+    if cont.attrs.type_from().is_some() && cont.attrs.type_try_from().is_some() {
+        cx.error_spanned_by(
+            cont.original,
+            "#[serde(from = \"...\")] and #[serde(try_from = \"...\")] conflict with each other",
+        );
+    }
+}

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")]
+  |                    ^^^^^^^^^^