feat(Value): Control key order

Fixes #159

Author: epage

Cargo.toml

@@ -29,6 +29,12 @@ default = ["extra-filters", "serde"]
 cli = ["clap", "error-chain", "serde_yaml"]
 extra-filters = []
 dev = []
+# Ensure keys in `Value`s `Object`s to be sorted.
+# Mutually exclusive with `object_order_preserved`
+object_sorted = []
+# Ensure the order that keys in `Value`s `Object`s are inserted is preserved
+# Mutually exclusive with `object_sorted`
+object_order_preserved = ["linked-hash-map"]
 
 [dependencies]
 regex = "0.2"
@@ -44,6 +50,8 @@ error-chain = { version = "0.11.0", optional = true }
 serde_yaml = { version = "0.7", optional = true }
 serde_json = { version = "1.0", optional = true }
 
+linked-hash-map = { version = "0.5", optional = true }
+
 [build-dependencies]
 skeptic = "0.13.2"
 serde = { version = "1.0", features = ["derive"] }

src/filters/mod.rs

@@ -598,7 +598,7 @@ pub fn pluralize(input: &Value, args: &[Value]) -> FilterResult {
 #[cfg(test)]
 mod tests {
 
-    use std::collections::HashMap;
+    use value::Object;
     use super::*;
 
     macro_rules! unit {
@@ -1371,7 +1371,7 @@ mod tests {
                          &[Value::scalar(1_f32)]),
                    Value::Array(vec![tos!("")]));
         assert_eq!(unit!(default,
-                         Value::Object(HashMap::new()),
+                         Value::Object(Object::new()),
                          &[Value::scalar(1_f32)]),
                    Value::scalar(1_f32));
         assert_eq!(unit!(default, Value::scalar(false), &[Value::scalar(1_f32)]),

src/lib.rs

@@ -44,6 +44,8 @@ extern crate lazy_static;
 extern crate serde;
 #[cfg(test)]
 extern crate serde_yaml;
+#[cfg(feature = "object_order_preserved")]
+extern crate linked_hash_map;
 
 mod error;
 mod filters;

src/tags/for_block.rs

@@ -1,4 +1,3 @@
-use std::collections::HashMap;
 use std::slice::Iter;
 
 use error::{Error, Result};
@@ -11,7 +10,7 @@ use compiler::Element;
 use compiler::LiquidOptions;
 use compiler::Token;
 use compiler::{parse, expect, split_block};
-use value::Value;
+use value::{Value, Object};
 
 #[derive(Clone, Debug)]
 enum Range {
@@ -95,7 +94,7 @@ impl Renderable for For {
             range_len => {
                 let mut ret = String::default();
                 context.run_in_scope(|mut scope| {
-                    let mut helper_vars: HashMap<String, Value> = HashMap::new();
+                    let mut helper_vars = Object::new();
                     helper_vars.insert("length".to_owned(), Value::scalar(range_len as i32));
 
                     for (i, v) in slice.iter().enumerate() {

src/tags/if_block.rs

@@ -155,9 +155,9 @@ pub fn if_block(_tag_name: &str,
 
 #[cfg(test)]
 mod test {
-    use std::collections::HashMap;
     use super::*;
     use value::Value;
+    use value::Object;
     use compiler;
     use interpreter;
 
@@ -418,7 +418,7 @@ mod test {
             .unwrap();
 
         let mut context = Context::new();
-        let mut obj = HashMap::new();
+        let mut obj = Object::new();
         obj.insert("Star Wars".to_owned(), Value::scalar("1977"));
         context.set_global_val("movies", Value::Object(obj));
         let output = template.render(&mut context).unwrap();
@@ -434,7 +434,7 @@ mod test {
             .unwrap();
 
         let mut context = Context::new();
-        let obj = HashMap::new();
+        let obj = Object::new();
         context.set_global_val("movies", Value::Object(obj));
         let output = template.render(&mut context).unwrap();
         assert_eq!(output, Some("if false".to_owned()));

src/value/values.rs

@@ -1,11 +1,28 @@
-use std::collections::HashMap;
 use std::cmp::Ordering;
 use std::fmt;
 use std::borrow;
 
+#[cfg(feature = "object_sorted")]
+use std::collections::BTreeMap;
+
+#[cfg(feature = "object_order_preserved")]
+use linked_hash_map::LinkedHashMap;
+
+#[cfg(not(any(feature = "object_order_preserved", feature = "object_sorted")))]
+use std::collections::HashMap;
+
 use super::Index;
 use super::Scalar;
 
+#[cfg(feature = "object_sorted")]
+type MapImpl<K, V> = BTreeMap<K, V>;
+
+#[cfg(feature = "object_order_preserved")]
+type MapImpl<K, V> = LinkedHashMap<K, V>;
+
+#[cfg(not(any(feature = "object_order_preserved", feature = "object_sorted")))]
+type MapImpl<K, V> = HashMap<K, V>;
+
 /// An enum to represent different value types
 #[derive(Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -21,7 +38,7 @@ pub enum Value {
 pub type Array = Vec<Value>;
 
 /// Type representing a Liquid object, payload of the `Value::Object` variant
-pub type Object = HashMap<String, Value>;
+pub type Object = MapImpl<String, Value>;
 
 impl Value {
     pub fn scalar<T: Into<Scalar>>(value: T) -> Self {