Added support for borrowing when flattening

serde_derive/src/de.rs

@@ -1875,7 +1875,9 @@ fn deserialize_identifier(
     collect_other_fields: bool
 ) -> Fragment {
     let field_strs = fields.iter().map(|&(ref name, _)| name);
+    let field_borrowed_strs = fields.iter().map(|&(ref name, _)| name);
     let field_bytes = fields.iter().map(|&(ref name, _)| Literal::byte_string(name.as_bytes()));
+    let field_borrowed_bytes = fields.iter().map(|&(ref name, _)| Literal::byte_string(name.as_bytes()));
 
     let constructors: &Vec<_> = &fields
         .iter()
@@ -1997,15 +1999,22 @@ fn deserialize_identifier(
         })
     };
 
-    let (value_as_str_content, value_as_bytes_content) = if !collect_other_fields {
+    let (value_as_str_content, value_as_borrowed_str_content,
-        (None, None)
+         value_as_bytes_content, value_as_borrowed_bytes_content) = if !collect_other_fields {
+        (None, None, None, None)
     } else {
         (
             Some(quote! {
                 let __value = _serde::private::de::Content::String(__value.to_string());
             }),
+            Some(quote! {
+                let __value = _serde::private::de::Content::Str(__value);
+            }),
             Some(quote! {
                 let __value = _serde::private::de::Content::ByteBuf(__value.to_vec());
+            }),
+            Some(quote! {
+                let __value = _serde::private::de::Content::Bytes(__value);
             })
         )
     };
@@ -2043,6 +2052,35 @@ fn deserialize_identifier(
             }
         }
 
+        fn visit_borrowed_str<__E>(self, __value: &'de str) -> _serde::export::Result<Self::Value, __E>
+            where __E: _serde::de::Error
+        {
+            match __value {
+                #(
+                    #field_borrowed_strs => _serde::export::Ok(#constructors),
+                )*
+                _ => {
+                    #value_as_borrowed_str_content
+                    #fallthrough_arm
+                }
+            }
+        }
+
+        fn visit_borrowed_bytes<__E>(self, __value: &'de [u8]) -> _serde::export::Result<Self::Value, __E>
+            where __E: _serde::de::Error
+        {
+            match __value {
+                #(
+                    #field_borrowed_bytes => _serde::export::Ok(#constructors),
+                )*
+                _ => {
+                    #bytes_to_str
+                    #value_as_borrowed_bytes_content
+                    #fallthrough_arm
+                }
+            }
+        }
+
         fn visit_bytes<__E>(self, __value: &[u8]) -> _serde::export::Result<Self::Value, __E>
             where __E: _serde::de::Error
         {

test_suite/tests/test_annotations.rs

@@ -1684,3 +1684,82 @@ fn test_non_string_keys() {
         ],
     );
 }
+
+#[test]
+fn test_lifetime_propagation_for_flatten() {
+    #[derive(Deserialize, Serialize, Debug, PartialEq)]
+    struct A<T> {
+        #[serde(flatten)]
+        t: T,
+    }
+
+    #[derive(Deserialize, Serialize, Debug, PartialEq)]
+    struct B<'a> {
+        #[serde(flatten, borrow)]
+        t: HashMap<&'a str, u32>,
+    }
+
+    #[derive(Deserialize, Serialize, Debug, PartialEq)]
+    struct C<'a> {
+        #[serde(flatten, borrow)]
+        t: HashMap<&'a [u8], u32>,
+    }
+
+    let mut owned_map = HashMap::new();
+    owned_map.insert("x".to_string(), 42u32);
+    assert_tokens(
+        &A { t: owned_map },
+        &[
+            Token::Map { len: None },
+            Token::Str("x"),
+            Token::U32(42),
+            Token::MapEnd,
+        ],
+    );
+
+    let mut borrowed_map = HashMap::new();
+    borrowed_map.insert("x", 42u32);
+    assert_ser_tokens(
+        &B { t: borrowed_map.clone() },
+        &[
+            Token::Map { len: None },
+            Token::BorrowedStr("x"),
+            Token::U32(42),
+            Token::MapEnd,
+        ],
+    );
+
+    assert_de_tokens(
+        &B { t: borrowed_map },
+        &[
+            Token::Map { len: None },
+            Token::BorrowedStr("x"),
+            Token::U32(42),
+            Token::MapEnd,
+        ],
+    );
+
+    let mut borrowed_map = HashMap::new();
+    borrowed_map.insert(&b"x"[..], 42u32);
+    assert_ser_tokens(
+        &C { t: borrowed_map.clone() },
+        &[
+            Token::Map { len: None },
+            Token::Seq { len: Some(1) },
+            Token::U8(120),
+            Token::SeqEnd,
+            Token::U32(42),
+            Token::MapEnd,
+        ],
+    );
+
+    assert_de_tokens(
+        &C { t: borrowed_map },
+        &[
+            Token::Map { len: None },
+            Token::BorrowedBytes(b"x"),
+            Token::U32(42),
+            Token::MapEnd,
+        ],
+    );
+}