From 6627540dd63f21800b7a0bc752d32b38f41c4c11 Mon Sep 17 00:00:00 2001
From: Jan Michael Auer <jan.auer@sentry.io>
Date: Thu, 15 Mar 2018 15:49:40 +0100
Subject: [PATCH] Added support basic deserialization in derive

---
 serde/src/de/mod.rs     |  7 +++++
 serde/src/export.rs     |  1 -
 serde_derive/src/de.rs  | 58 ++++++++++++++++++++++++++++-------------
 serde_derive/src/ser.rs |  2 +-
 4 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/serde/src/de/mod.rs b/serde/src/de/mod.rs
index cc2c6502..162d4ad4 100644
--- a/serde/src/de/mod.rs
+++ b/serde/src/de/mod.rs
@@ -255,6 +255,13 @@ macro_rules! declare_error_trait {
                 }
             }
 
+            /// Raised when a `Deserialize` struct type recieved a field with an
+            /// unrecognized name but the names are not actually known because of
+            /// flattening.
+            fn unknow_field_in_flattened_structure(field: &str) -> Self {
+                Error::custom(format_args!("unknown field `{}`", field))
+            }
+
             /// Raised when a `Deserialize` struct type expected to receive a required
             /// field with a particular name but that field was not present in the
             /// input.
diff --git a/serde/src/export.rs b/serde/src/export.rs
index e92b647d..772f3103 100644
--- a/serde/src/export.rs
+++ b/serde/src/export.rs
@@ -13,7 +13,6 @@ pub use lib::fmt::{self, Formatter};
 pub use lib::marker::PhantomData;
 pub use lib::option::Option::{self, None, Some};
 pub use lib::result::Result::{self, Err, Ok};
-pub use lib::iter::once;
 
 pub use self::string::from_utf8_lossy;
 
diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
index 606b0f4e..7ced726a 100644
--- a/serde_derive/src/de.rs
+++ b/serde_derive/src/de.rs
@@ -1711,7 +1711,7 @@ fn deserialize_generated_identifier(
 
     let (ignore_variant, fallthrough, want_value) = if is_variant || cattrs.deny_unknown_fields() {
         (None, None, false)
-    } else if cattrs.unknown_fields_into().is_some() {
+    } else if cattrs.has_flatten() {
         let ignore_variant = quote!(__other(String),);
         let fallthrough = quote!(_serde::export::Ok(__Field::__other(__value.to_string())));
         (Some(ignore_variant), Some(fallthrough), true)
@@ -2023,18 +2023,14 @@ fn deserialize_map(
             }
         });
 
-    // If we have a collect into, we also need a container that can
-    // hold the data we accumulate.
-    let mut let_collect = None;
-    for &(field, _) in fields_names.iter() {
-        if field.attrs.collection_field() {
-            let field_ty = &field.ty;
-            let_collect = Some(quote! {
-                let mut __collect: #field_ty = Default::default();
-            });
-            break;
-        }
-    }
+    // Collect contents for flatten fields into a buffer
+    let let_collect = if cattrs.has_flatten() {
+        Some(quote! {
+            let mut __collect = Vec::<_serde::private::de::Content>::new();
+        })
+    } else {
+        None
+    };
 
     // Match arms to extract a value for a field.
     let value_arms = fields_names
@@ -2073,10 +2069,10 @@ fn deserialize_map(
     // Visit ignored values to consume them
     let ignored_arm = if cattrs.deny_unknown_fields() {
         None
-    } else if cattrs.unknown_fields_into().is_some() {
+    } else if cattrs.has_flatten() {
         Some(quote! {
             __Field::__other(__name) => {
-                __collect.extend(_serde::export::once((__name, try!(_serde::de::MapAccess::next_value(&mut __map)))));
+                __collect.push((__name, try!(_serde::de::MapAccess::next_value(&mut __map))));
             }
         })
     } else {
@@ -2119,11 +2115,33 @@ fn deserialize_map(
             }
         });
 
+    let extract_collected = fields_names
+        .iter()
+        .filter(|&&(field, _)| field.attrs.flatten())
+        .map(|&(field, ref name)| {
+            let field_ty = field.ty;
+            quote! {
+                let #name: #field_ty = try!(_serde::de::Deserialize::deserialize(
+                    _serde::private::de::FlatMapDeserializer::new(
+                        &mut __collect,
+                        _serde::export::PhantomData)));
+            }
+        });
+
+    let collected_deny_unknown_fields = if cattrs.deny_unknown_fields() {
+        Some(quote! {
+            if let Some((__key, _)) = __collect.into_iter().next() {
+                return _serde::export::Err(
+                    _serde::de::Error::unknown_field_in_flattened_structure(__key));
+            }
+        })
+    } else {
+        None
+    };
+
     let result = fields_names.iter().map(|&(field, ref name)| {
         let ident = field.ident.expect("struct contains unnamed fields");
-        if field.attrs.collection_field() {
-            quote_spanned!(Span::def_site()=> #ident: __collect)
-        } else if field.attrs.skip_deserializing() {
+        if field.attrs.skip_deserializing() && !field.attrs.flatten() {
             let value = Expr(expr_is_missing(field, cattrs));
             quote_spanned!(Span::call_site()=> #ident: #value)
         } else {
@@ -2164,6 +2182,10 @@ fn deserialize_map(
 
         #(#extract_values)*
 
+        #(#extract_collected)*
+
+        #collected_deny_unknown_fields
+
         _serde::export::Ok(#result)
     }
 }
diff --git a/serde_derive/src/ser.rs b/serde_derive/src/ser.rs
index eb938816..20d22ff6 100644
--- a/serde_derive/src/ser.rs
+++ b/serde_derive/src/ser.rs
@@ -925,7 +925,7 @@ fn serialize_struct_visitor(
             let span = Span::def_site().located_at(field.original.span());
             let ser = if field.attrs.flatten() {
                 quote! {
-                    try!((#field_expr).serialize(_serde::private::ser::FlatSerializer(&mut __serde_state)));
+                    try!((#field_expr).serialize(_serde::private::ser::FlatSerializer::new(&mut __serde_state)));
                 }
             } else {
                 let func = struct_trait.serialize_field(span);