feat(codegen): Add support for #![serde(skip_serialize_if="$expr")]

This allows end users to use an arbitrary expression to decide whether or not to serialize some field. This expression has access to all the fields in the struct, but none of the internal state of the Serialize implementation. For structs, serde implements this by creating a temporary trait and implementing the struct for it. For struct variants, the fields are copied by reference into a temporary struct first before implementing the temporary trait. This also fixes a bug where the serde_codegen wasn't making calls to Serializer::serialize_{tuple,struct}_variant{,_elt}.
2026-04-25 01:07:56 +00:00 · 2016-02-12 22:05:02 -08:00
parent 9812a4c9c6
commit de89f95f31
8 changed files with 761 additions and 305 deletions
@@ -166,6 +166,7 @@ pub struct FieldAttrs {
    serialize_name: Option<ast::Lit>,
    deserialize_name: Option<ast::Lit>,
    skip_serializing_field: bool,
+    skip_serializing_field_if: Option<P<ast::Expr>>,
    skip_serializing_field_if_empty: bool,
    skip_serializing_field_if_none: bool,
    default_expr_if_missing: Option<P<ast::Expr>>,
@@ -174,6 +175,7 @@ pub struct FieldAttrs {
 impl FieldAttrs {
    /// Extract out the `#[serde(...)]` attributes from a struct field.
    pub fn from_field(cx: &ExtCtxt,
+                      container_ty: &P<ast::Ty>,
                      generics: &ast::Generics,
                      field: &ast::StructField) -> Result<Self, Error> {
        let builder = AstBuilder::new();
@@ -188,6 +190,7 @@ impl FieldAttrs {
            serialize_name: None,
            deserialize_name: None,
            skip_serializing_field: false,
+            skip_serializing_field_if: None,
            skip_serializing_field_if_empty: false,
            skip_serializing_field_if_none: false,
            default_expr_if_missing: None,
@@ -232,6 +235,18 @@ impl FieldAttrs {
                        field_attrs.skip_serializing_field = true;
                    }

+                    // Parse `#[serde(skip_serializing_if="...")]`
+                    ast::MetaItemKind::NameValue(ref name, ref lit) if name == &"skip_serializing_if" => {
+                        let expr = wrap_skip_serializing(
+                            cx,
+                            container_ty,
+                            generics,
+                            try!(parse_lit_into_expr(cx, name, lit)),
+                        );
+
+                        field_attrs.skip_serializing_field_if = Some(expr);
+                    }
+
                    // Parse `#[serde(skip_serializing_if_none)]`
                    ast::MetaItemKind::Word(ref name) if name == &"skip_serializing_if_none" => {
                        field_attrs.skip_serializing_field_if_none = true;
@@ -298,6 +313,10 @@ impl FieldAttrs {
        self.skip_serializing_field
    }

+    pub fn skip_serializing_field_if(&self) -> Option<&P<ast::Expr>> {
+        self.skip_serializing_field_if.as_ref()
+    }
+
    pub fn skip_serializing_field_if_empty(&self) -> bool {
        self.skip_serializing_field_if_empty
    }
@@ -307,12 +326,14 @@ impl FieldAttrs {
    }
 }

+
 /// Extract out the `#[serde(...)]` attributes from a struct field.
 pub fn get_struct_field_attrs(cx: &ExtCtxt,
+                              container_ty: &P<ast::Ty>,
                              generics: &ast::Generics,
                              fields: &[ast::StructField]) -> Result<Vec<FieldAttrs>, Error> {
    fields.iter()
-        .map(|field| FieldAttrs::from_field(cx, generics, field))
+        .map(|field| FieldAttrs::from_field(cx, container_ty, generics, field))
        .collect()
 }

@@ -401,3 +422,26 @@ fn wrap_default(cx: &ExtCtxt,
        $fn_path()
    })
 }
+
+/// This function wraps the expression in `#[serde(skip_serializing_if="...")]` in a trait to
+/// prevent it from accessing the internal `Serialize` state.
+fn wrap_skip_serializing(cx: &ExtCtxt,
+                         container_ty: &P<ast::Ty>,
+                         generics: &ast::Generics,
+                         expr: P<ast::Expr>) -> P<ast::Expr> {
+    let where_clause = &generics.where_clause;
+
+    quote_expr!(cx, {
+        trait __SerdeShouldSkipSerializing {
+            fn __serde_should_skip_serializing(&self) -> bool;
+        }
+
+        impl $generics __SerdeShouldSkipSerializing for $container_ty $where_clause {
+            fn __serde_should_skip_serializing(&self) -> bool {
+                $expr
+            }
+        }
+
+        self.value.__serde_should_skip_serializing()
+    })
+}
@@ -503,6 +503,7 @@ fn deserialize_struct(
        cx,
        builder,
        type_path.clone(),
+        &ty,
        impl_generics,
        fields,
        container_attrs
@@ -757,6 +758,7 @@ fn deserialize_struct_variant(
        cx,
        builder,
        type_path,
+        &ty,
        generics,
        fields,
        container_attrs,
@@ -920,13 +922,19 @@ fn deserialize_struct_visitor(
    cx: &ExtCtxt,
    builder: &aster::AstBuilder,
    struct_path: ast::Path,
+    container_ty: &P<ast::Ty>,
    generics: &ast::Generics,
    fields: &[ast::StructField],
    container_attrs: &attr::ContainerAttrs,
 ) -> Result<(Vec<P<ast::Item>>, ast::Stmt, P<ast::Expr>), Error> {
    let field_exprs = fields.iter()
        .map(|field| {
-            let field_attrs = try!(attr::FieldAttrs::from_field(cx, generics, field));
+            let field_attrs = try!(
+                attr::FieldAttrs::from_field(cx,
+                                             container_ty,
+                                             generics,
+                                             field)
+            );
            Ok(field_attrs.deserialize_name_expr())
        })
        .collect();
@@ -942,6 +950,7 @@ fn deserialize_struct_visitor(
        cx,
        builder,
        struct_path,
+        container_ty,
        generics,
        fields,
        container_attrs,
@@ -972,6 +981,7 @@ fn deserialize_map(
    cx: &ExtCtxt,
    builder: &aster::AstBuilder,
    struct_path: ast::Path,
+    container_ty: &P<ast::Ty>,
    generics: &ast::Generics,
    fields: &[ast::StructField],
    container_attrs: &attr::ContainerAttrs,
@@ -1011,7 +1021,12 @@ fn deserialize_map(
    let extract_values = fields.iter()
        .zip(field_names.iter())
        .map(|(field, field_name)| {
-            let field_attr = try!(attr::FieldAttrs::from_field(cx, generics, field));
+            let field_attr = try!(
+                attr::FieldAttrs::from_field(cx,
+                                             container_ty,
+                                             generics,
+                                             field)
+            );
            let missing_expr = field_attr.expr_is_missing();

            Ok(quote_stmt!(cx,
@@ -33,14 +33,30 @@ pub fn expand_derive_serialize(

    let builder = aster::AstBuilder::new().span(span);

+    let impl_item = match serialize_item(cx, &builder, &item) {
+        Ok(item) => item,
+        Err(Error) => {
+            // An error occured, but it should have been reported already.
+            return;
+        }
+    };
+
+    push(Annotatable::Item(impl_item))
+}
+
+fn serialize_item(
+    cx: &ExtCtxt,
+    builder: &aster::AstBuilder,
+    item: &Item,
+) -> Result<P<ast::Item>, Error> {
    let generics = match item.node {
        ast::ItemKind::Struct(_, ref generics) => generics,
        ast::ItemKind::Enum(_, ref generics) => generics,
        _ => {
            cx.span_err(
-                meta_item.span,
+                item.span,
                "`#[derive(Serialize)]` may only be applied to structs and enums");
-            return;
+            return Err(Error);
        }
    };

@@ -54,17 +70,15 @@ pub fn expand_derive_serialize(
        .segment(item.ident).with_generics(impl_generics.clone()).build()
        .build();

-    let body = match serialize_body(cx, &builder, &item, &impl_generics, ty.clone()) {
-        Ok(body) => body,
-        Err(Error) => {
-            // An error occured, but it should have been reported already.
-            return;
-        }
-    };
+    let body = try!(serialize_body(cx,
+                                   &builder,
+                                   &item,
+                                   &impl_generics,
+                                   ty.clone()));

    let where_clause = &impl_generics.where_clause;

-    let impl_item = quote_item!(cx,
+    Ok(quote_item!(cx,
        impl $impl_generics ::serde::ser::Serialize for $ty $where_clause {
            fn serialize<__S>(&self, serializer: &mut __S) -> ::std::result::Result<(), __S::Error>
                where __S: ::serde::ser::Serializer,
@@ -72,9 +86,7 @@ pub fn expand_derive_serialize(
                $body
            }
        }
-    ).unwrap();
-
-    push(Annotatable::Item(impl_item))
+    ).unwrap())
 }

 fn serialize_body(
@@ -207,6 +219,7 @@ fn serialize_tuple_struct(
            .ref_()
            .lifetime("'__a")
            .build_ty(ty.clone()),
+        builder.id("serialize_tuple_struct_elt"),
        fields,
        impl_generics,
    );
@@ -232,11 +245,6 @@ fn serialize_struct(
    fields: &[ast::StructField],
    container_attrs: &attr::ContainerAttrs,
 ) -> Result<P<ast::Expr>, Error> {
-    let value_exprs = fields.iter().map(|field| {
-        let name = field.node.ident().expect("struct has unnamed field");
-        quote_expr!(cx, &self.value.$name)
-    });
-
    let (visitor_struct, visitor_impl) = try!(serialize_struct_visitor(
        cx,
        builder,
@@ -245,9 +253,9 @@ fn serialize_struct(
            .ref_()
            .lifetime("'__a")
            .build_ty(ty.clone()),
+        builder.id("serialize_struct_elt"),
        fields,
        impl_generics,
-        value_exprs,
    ));

    let type_name = container_attrs.serialize_name_expr();
@@ -272,22 +280,23 @@ fn serialize_item_enum(
    enum_def: &ast::EnumDef,
    container_attrs: &attr::ContainerAttrs,
 ) -> Result<P<ast::Expr>, Error> {
-    let mut arms = vec![];
-
-    for (variant_index, variant) in enum_def.variants.iter().enumerate() {
-        let arm = try!(serialize_variant(
-            cx,
-            builder,
-            type_ident,
-            impl_generics,
-            ty.clone(),
-            variant,
-            variant_index,
-            container_attrs,
-        ));
-
-        arms.push(arm);
-    }
+    let arms: Vec<_> = try!(
+        enum_def.variants.iter()
+            .enumerate()
+            .map(|(variant_index, variant)| {
+                serialize_variant(
+                    cx,
+                    builder,
+                    type_ident,
+                    impl_generics,
+                    ty.clone(),
+                    variant,
+                    variant_index,
+                    container_attrs,
+                )
+            })
+            .collect()
+    );

    Ok(quote_expr!(cx,
        match *self {
@@ -404,13 +413,13 @@ fn serialize_variant(
            let expr = try!(serialize_struct_variant(
                cx,
                builder,
-                type_name,
                variant_index,
                variant_name,
                generics,
                ty,
                fields,
                field_names,
+                container_attrs,
            ));

            Ok(quote_arm!(cx,
@@ -447,6 +456,7 @@ fn serialize_tuple_variant(
        builder,
        structure_ty.clone(),
        variant_ty,
+        builder.id("serialize_tuple_variant_elt"),
        fields.len(),
        generics,
    );
@@ -473,55 +483,88 @@ fn serialize_tuple_variant(
 fn serialize_struct_variant(
    cx: &ExtCtxt,
    builder: &aster::AstBuilder,
-    type_name: P<ast::Expr>,
    variant_index: usize,
    variant_name: P<ast::Expr>,
    generics: &ast::Generics,
-    structure_ty: P<ast::Ty>,
+    ty: P<ast::Ty>,
    fields: &[ast::StructField],
    field_names: Vec<Ident>,
+    container_attrs: &attr::ContainerAttrs,
 ) -> Result<P<ast::Expr>, Error> {
-    let value_ty = builder.ty().tuple()
-        .with_tys(
+    let variant_generics = builder.generics()
+        .with(generics.clone())
+        .add_lifetime_bound("'__serde_variant")
+        .lifetime_name("'__serde_variant")
+        .build();
+
+    let variant_struct = builder.item().struct_("__VariantStruct")
+        .with_generics(variant_generics.clone())
+        .with_fields(
            fields.iter().map(|field| {
-                builder.ty()
+                builder.struct_field(field.node.ident().expect("struct has unnamed fields"))
+                    .with_attrs(field.node.attrs.iter().cloned())
+                    .ty()
                    .ref_()
-                    .lifetime("'__a")
+                    .lifetime("'__serde_variant")
                    .build_ty(field.node.ty.clone())
            })
        )
+        .field("__serde_container_ty")
+            .ty().phantom_data().build(ty.clone())
        .build();

-    let value_expr = builder.expr().tuple()
-        .with_exprs(
-            field_names.iter().map(|field| {
-                builder.expr().id(field)
-            })
+    let variant_expr = builder.expr().struct_id("__VariantStruct")
+        .with_id_exprs(
+            fields.iter()
+                .zip(field_names.iter())
+                .map(|(field, field_name)| {
+                    (
+                        field.node.ident().expect("struct has unnamed fields"),
+                        builder.expr().id(field_name),
+                    )
+                })
        )
+        .field("__serde_container_ty").path()
+            .global()
+            .id("std").id("marker")
+            .segment("PhantomData")
+                .with_ty(ty.clone())
+                .build()
+            .build()
+        .build();
+
+    let variant_ty = builder.ty().path()
+        .segment("__VariantStruct")
+            .with_generics(variant_generics.clone())
+            .build()
        .build();

    let (visitor_struct, visitor_impl) = try!(serialize_struct_visitor(
        cx,
        builder,
-        structure_ty.clone(),
-        value_ty,
+        variant_ty.clone(),
+        variant_ty.clone(),
+        builder.id("serialize_struct_variant_elt"),
        fields,
-        generics,
-        (0 .. field_names.len()).map(|i| {
-            builder.expr()
-                .tup_field(i)
-                .field("value").self_()
-        })
+        &variant_generics,
    ));

+    let container_name = container_attrs.serialize_name_expr();
+
    Ok(quote_expr!(cx, {
+        $variant_struct
        $visitor_struct
        $visitor_impl
-        serializer.serialize_struct_variant($type_name, $variant_index, $variant_name, Visitor {
-            value: $value_expr,
-            state: 0,
-            _structure_ty: ::std::marker::PhantomData::<&$structure_ty>,
-        })
+        serializer.serialize_struct_variant(
+            $container_name,
+            $variant_index,
+            $variant_name,
+            Visitor {
+                value: $variant_expr,
+                state: 0,
+                _structure_ty: ::std::marker::PhantomData,
+            },
+        )
    }))
 }

@@ -530,20 +573,21 @@ fn serialize_tuple_struct_visitor(
    builder: &aster::AstBuilder,
    structure_ty: P<ast::Ty>,
    variant_ty: P<ast::Ty>,
+    serializer_method: ast::Ident,
    fields: usize,
    generics: &ast::Generics
 ) -> (P<ast::Item>, P<ast::Item>) {
    let arms: Vec<ast::Arm> = (0 .. fields)
        .map(|i| {
-            let expr = builder.expr()
-                .tup_field(i)
-                .field("value").self_();
+            let expr = builder.expr().method_call(serializer_method)
+                .id("serializer")
+                .arg().ref_().tup_field(i).field("value").self_()
+                .build();

            quote_arm!(cx,
                $i => {
                    self.state += 1;
-                    let v = try!(serializer.serialize_tuple_struct_elt(&$expr));
-                    Ok(Some(v))
+                    Ok(Some(try!($expr)))
                }
            )
        })
@@ -592,51 +636,51 @@ fn serialize_tuple_struct_visitor(
    )
 }

-fn serialize_struct_visitor<I>(
+fn serialize_struct_visitor(
    cx: &ExtCtxt,
    builder: &aster::AstBuilder,
    structure_ty: P<ast::Ty>,
    variant_ty: P<ast::Ty>,
+    serializer_method: ast::Ident,
    fields: &[ast::StructField],
    generics: &ast::Generics,
-    value_exprs: I,
-) -> Result<(P<ast::Item>, P<ast::Item>), Error>
-    where I: Iterator<Item=P<ast::Expr>>,
-{
-    let value_exprs = value_exprs.collect::<Vec<_>>();
+) -> Result<(P<ast::Item>, P<ast::Item>), Error> {
+    let field_attrs = try!(
+        attr::get_struct_field_attrs(cx, &structure_ty, generics, fields)
+    );

-    let field_attrs = try!(attr::get_struct_field_attrs(cx, generics, fields));
-
-    let arms: Vec<ast::Arm> = field_attrs.iter()
-        .zip(value_exprs.iter())
-        .filter(|&(ref field, _)| !field.skip_serializing_field())
+    let arms: Vec<ast::Arm> = fields.iter().zip(field_attrs.iter())
+        .filter(|&(_, ref field_attr)| !field_attr.skip_serializing_field())
        .enumerate()
-        .map(|(i, (ref field, value_expr))| {
-            let key_expr = field.serialize_name_expr();
+        .map(|(i, (ref field, ref field_attr))| {
+            let name = field.node.ident().expect("struct has unnamed field");

-            let stmt = if field.skip_serializing_field_if_empty() {
-                quote_stmt!(cx, if ($value_expr).is_empty() { continue; })
-            } else if field.skip_serializing_field_if_none() {
-                quote_stmt!(cx, if ($value_expr).is_none() { continue; })
-            } else {
-                quote_stmt!(cx, {})
+            let key_expr = field_attr.serialize_name_expr();
+
+            let stmt = match field_attr.skip_serializing_field_if() {
+                Some(expr) => {
+                    Some(quote_stmt!(cx, if $expr { continue; }))
+                }
+                None => {
+                    if field_attr.skip_serializing_field_if_empty() {
+                        Some(quote_stmt!(cx, if self.value.$name.is_empty() { continue; }))
+                    } else if field_attr.skip_serializing_field_if_none() {
+                        Some(quote_stmt!(cx, if self.value.$name.is_none() { continue; }))
+                    } else {
+                        None
+                    }
+                }
            };

+            let expr = quote_expr!(cx,
+                serializer.$serializer_method($key_expr, &self.value.$name)
+            );
+
            quote_arm!(cx,
                $i => {
                    self.state += 1;
                    $stmt
-
-                    return Ok(
-                        Some(
-                            try!(
-                                serializer.serialize_struct_elt(
-                                    $key_expr,
-                                    $value_expr,
-                                )
-                            )
-                        )
-                    );
+                    return Ok(Some(try!($expr)));
                }
            )
        })
@@ -653,17 +697,27 @@ fn serialize_struct_visitor<I>(
        .strip_bounds()
        .build();

-    let len = field_attrs.iter()
-        .zip(value_exprs.iter())
-        .map(|(field, value_expr)| {
-            if field.skip_serializing_field() {
+    let len = fields.iter().zip(field_attrs.iter())
+        .map(|(field, field_attr)| {
+            if field_attr.skip_serializing_field() {
                quote_expr!(cx, 0)
-            } else if field.skip_serializing_field_if_empty() {
-                quote_expr!(cx, if ($value_expr).is_empty() { 0 } else { 1 })
-            } else if field.skip_serializing_field_if_none() {
-                quote_expr!(cx, if ($value_expr).is_none() { 0 } else { 1 })
            } else {
-                quote_expr!(cx, 1)
+                match field_attr.skip_serializing_field_if() {
+                    Some(expr) => {
+                        quote_expr!(cx, if $expr { 0 } else { 1 })
+                    }
+                    None => {
+                        let name = field.node.ident().expect("struct has unnamed field");
+
+                        if field_attr.skip_serializing_field_if_empty() {
+                            quote_expr!(cx, if self.value.$name.is_empty() { 0 } else { 1 })
+                        } else if field_attr.skip_serializing_field_if_none() {
+                            quote_expr!(cx, if self.value.$name.is_none() { 0 } else { 1 })
+                        } else {
+                            quote_expr!(cx, 1)
+                        }
+                    }
+                }
            }
        })
        .fold(quote_expr!(cx, 0), |sum, expr| quote_expr!(cx, $sum + $expr));