Add a serialization helper to put tables last

This should help serializing maps where it's unknown up front whether the tables
and/or values come first.

Closes #142
This commit is contained in:
Alex Crichton 2017-02-10 15:29:36 -08:00
parent 5906fa71b5
commit 67fb9f1953
2 changed files with 296 additions and 2 deletions

View file

@ -3,10 +3,33 @@
//! This module contains all the Serde support for serializing Rust structures
//! into TOML documents (as strings). Note that some top-level functions here
//! are also provided at the top of the crate.
//!
//! Note that the TOML format has a restriction that if a table itself contains
//! tables, all keys with non-table values must be emitted first. This is
//! typically easy to ensure happens when you're defining a `struct` as you can
//! reorder the fields manually, but when working with maps (such as `BTreeMap`
//! or `HashMap`) this can lead to serialization errors. In those situations you
//! may use the `tables_last` function in this module like so:
//!
//! ```rust
//! # #[macro_use] extern crate serde_derive;
//! # extern crate toml;
//! # use std::collections::HashMap;
//! #[derive(Serialize)]
//! struct Manifest {
//! package: Package,
//! #[serde(serialize_with = "toml::ser::tables_last")]
//! dependencies: HashMap<String, Dependency>,
//! }
//! # type Package = String;
//! # type Dependency = String;
//! # fn main() {}
//! ```
use std::fmt::{self, Write};
use std::error;
use std::cell::Cell;
use std::error;
use std::fmt::{self, Write};
use std::marker;
use serde::ser;
use datetime::{SERDE_STRUCT_FIELD_NAME, SERDE_STRUCT_NAME};
@ -1004,3 +1027,244 @@ impl ser::Error for Error {
Error::Custom(msg.to_string())
}
}
enum Category {
Primitive,
Array,
Table,
}
/// Convenience function to serialize items in a map in an order valid with
/// TOML.
///
/// TOML carries the restriction that keys in a table must be serialized last if
/// their value is a table itself. This isn't always easy to guarantee, so this
/// helper can be used like so:
///
/// ```rust
/// # #[macro_use] extern crate serde_derive;
/// # extern crate toml;
/// # use std::collections::HashMap;
/// #[derive(Serialize)]
/// struct Manifest {
/// package: Package,
/// #[serde(serialize_with = "toml::ser::tables_last")]
/// dependencies: HashMap<String, Dependency>,
/// }
/// # type Package = String;
/// # type Dependency = String;
/// # fn main() {}
/// ```
pub fn tables_last<'a, I, K, V, S>(data: &'a I, serializer: S)
-> Result<S::Ok, S::Error>
where &'a I: IntoIterator<Item = (K, V)>,
K: ser::Serialize,
V: ser::Serialize,
S: ser::Serializer
{
use serde::ser::SerializeMap;
let mut map = serializer.serialize_map(None)?;
for (k, v) in data {
if let Category::Primitive = v.serialize(Categorize::new())? {
map.serialize_entry(&k, &v)?;
}
}
for (k, v) in data {
if let Category::Array = v.serialize(Categorize::new())? {
map.serialize_entry(&k, &v)?;
}
}
for (k, v) in data {
if let Category::Table = v.serialize(Categorize::new())? {
map.serialize_entry(&k, &v)?;
}
}
map.end()
}
struct Categorize<E>(marker::PhantomData<E>);
impl<E> Categorize<E> {
fn new() -> Self {
Categorize(marker::PhantomData)
}
}
impl<E: ser::Error> ser::Serializer for Categorize<E> {
type Ok = Category;
type Error = E;
type SerializeSeq = Self;
type SerializeTuple = ser::Impossible<Category, E>;
type SerializeTupleStruct = ser::Impossible<Category, E>;
type SerializeTupleVariant = ser::Impossible<Category, E>;
type SerializeMap = Self;
type SerializeStruct = Self;
type SerializeStructVariant = ser::Impossible<Category, E>;
fn serialize_bool(self, _: bool) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_i8(self, _: i8) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_i16(self, _: i16) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_i32(self, _: i32) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_i64(self, _: i64) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_u8(self, _: u8) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_u16(self, _: u16) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_u32(self, _: u32) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_u64(self, _: u64) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_f32(self, _: f32) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_f64(self, _: f64) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_char(self, _: char) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_str(self, _: &str) -> Result<Self::Ok, Self::Error> {
Ok(Category::Primitive)
}
fn serialize_bytes(self, _: &[u8]) -> Result<Self::Ok, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_some<T: ?Sized + ser::Serialize>(self, v: &T) -> Result<Self::Ok, Self::Error> {
v.serialize(self)
}
fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_unit_struct(self, _: &'static str) -> Result<Self::Ok, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_unit_variant(self, _: &'static str, _: usize, _: &'static str) -> Result<Self::Ok, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_newtype_struct<T: ?Sized + ser::Serialize>(self, _: &'static str, v: &T) -> Result<Self::Ok, Self::Error> {
v.serialize(self)
}
fn serialize_newtype_variant<T: ?Sized + ser::Serialize>(self, _: &'static str, _: usize, _: &'static str, _: &T) -> Result<Self::Ok, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_seq(self, _: Option<usize>) -> Result<Self, Self::Error> {
Ok(self)
}
fn serialize_seq_fixed_size(self, _: usize) -> Result<Self, Self::Error> {
Ok(self)
}
fn serialize_tuple(self, _: usize) -> Result<Self::SerializeTuple, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_tuple_struct(self, _: &'static str, _: usize) -> Result<Self::SerializeTupleStruct, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_tuple_variant(self, _: &'static str, _: usize, _: &'static str, _: usize) -> Result<Self::SerializeTupleVariant, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
fn serialize_map(self, _: Option<usize>) -> Result<Self, Self::Error> {
Ok(self)
}
fn serialize_struct(self, _: &'static str, _: usize) -> Result<Self, Self::Error> {
Ok(self)
}
fn serialize_struct_variant(self, _: &'static str, _: usize, _: &'static str, _: usize) -> Result<Self::SerializeStructVariant, Self::Error> {
Err(ser::Error::custom("unsupported"))
}
}
impl<E: ser::Error> ser::SerializeSeq for Categorize<E> {
type Ok = Category;
type Error = E;
fn serialize_element<T: ?Sized + ser::Serialize>(&mut self, _: &T)
-> Result<(), Self::Error> {
Ok(())
}
fn end(self) -> Result<Self::Ok, Self::Error> {
Ok(Category::Array)
}
}
impl<E: ser::Error> ser::SerializeMap for Categorize<E> {
type Ok = Category;
type Error = E;
fn serialize_key<T: ?Sized + ser::Serialize>(&mut self, _: &T)
-> Result<(), Self::Error> {
Ok(())
}
fn serialize_value<T: ?Sized + ser::Serialize>(&mut self, _: &T)
-> Result<(), Self::Error> {
Ok(())
}
fn end(self) -> Result<Self::Ok, Self::Error> {
Ok(Category::Table)
}
}
impl<E: ser::Error> ser::SerializeStruct for Categorize<E> {
type Ok = Category;
type Error = E;
fn serialize_field<T: ?Sized>(&mut self,
_: &'static str,
_: &T) -> Result<(), Self::Error>
where T: ser::Serialize,
{
Ok(())
}
fn end(self) -> Result<Self::Ok, Self::Error> {
Ok(Category::Table)
}
}

30
tests/tables-last.rs Normal file
View file

@ -0,0 +1,30 @@
#[macro_use]
extern crate serde_derive;
extern crate toml;
use std::collections::HashMap;
#[derive(Serialize)]
struct A {
#[serde(serialize_with = "toml::ser::tables_last")]
vals: HashMap<&'static str, Value>,
}
#[derive(Serialize)]
#[serde(untagged)]
enum Value {
Map(HashMap<&'static str, &'static str>),
Int(i32),
}
#[test]
fn always_works() {
let mut a = A { vals: HashMap::new() };
a.vals.insert("foo", Value::Int(0));
let mut sub = HashMap::new();
sub.insert("foo", "bar");
a.vals.insert("bar", Value::Map(sub));
toml::to_string(&a).unwrap();
}