git.delta.rocks / jrsonnet / refs/commits / 90e93cc51b3a

--- a/Cargo.lock
+++ b/Cargo.lock
@@ -492,6 +492,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0ffa0837f2dfa6fb90868c2b5468cad482e175f7dad97e7421951e663f2b527"
 dependencies = [
+ "indexmap",
  "itoa",
  "ryu",
  "serde",

--- a/bindings/jsonnet/Cargo.toml
+++ b/bindings/jsonnet/Cargo.toml
@@ -17,3 +17,4 @@
 
 [features]
 interop = []
+exp-preserve-order = ["jrsonnet-evaluator/exp-preserve-order"]

--- a/bindings/jsonnet/src/lib.rs
+++ b/bindings/jsonnet/src/lib.rs
@@ -58,7 +58,11 @@
 pub extern "C" fn jsonnet_string_output(vm: &EvaluationState, v: c_int) {
 	match v {
 		1 => vm.set_manifest_format(ManifestFormat::String),
-		0 => vm.set_manifest_format(ManifestFormat::Json(4)),
+		0 => vm.set_manifest_format(ManifestFormat::Json {
+			padding: 4,
+			#[cfg(feature = "exp-preserve-order")]
+			preserve_order: false,
+		}),
 		_ => panic!("incorrect output format"),
 	}
 }

--- a/bindings/jsonnet/src/val_modify.rs
+++ b/bindings/jsonnet/src/val_modify.rs
@@ -5,8 +5,7 @@
 use std::{ffi::CStr, os::raw::c_char};
 
 use gcmodule::Cc;
-use jrsonnet_evaluator::{val::ArrValue, EvaluationState, LazyBinding, LazyVal, ObjMember, Val};
-use jrsonnet_parser::Visibility;
+use jrsonnet_evaluator::{val::ArrValue, EvaluationState, LazyVal, Val};
 
 /// # Safety
 ///
@@ -41,19 +40,9 @@
 	val: &Val,
 ) {
 	match obj {
-		Val::Obj(old) => {
-			let new_obj = old.clone().extend_with_field(
-				CStr::from_ptr(name).to_str().unwrap().into(),
-				ObjMember {
-					add: false,
-					visibility: Visibility::Normal,
-					invoke: LazyBinding::Bound(LazyVal::new_resolved(val.clone())),
-					location: None,
-				},
-			);
-
-			*obj = Val::Obj(new_obj);
-		}
+		Val::Obj(old) => old
+			.extend_field(CStr::from_ptr(name).to_str().unwrap().into())
+			.value(val.clone()),
 		_ => panic!("should receive object"),
 	}
 }

--- a/cmds/jrsonnet/Cargo.toml
+++ b/cmds/jrsonnet/Cargo.toml
@@ -9,6 +9,12 @@
 [features]
 # Use mimalloc as allocator
 mimalloc = ["mimallocator"]
+# Experimental feature, which allows to preserve order of object fields
+exp-preserve-order = [
+    "jrsonnet-evaluator/exp-preserve-order",
+    "jrsonnet-evaluator/exp-serde-preserve-order",
+    "jrsonnet-cli/exp-preserve-order",
+]
 
 [dependencies]
 jrsonnet-evaluator = { path = "../../crates/jrsonnet-evaluator", version = "0.4.2" }

--- a/crates/jrsonnet-cli/Cargo.toml
+++ b/crates/jrsonnet-cli/Cargo.toml
@@ -6,6 +6,9 @@
 license = "MIT"
 edition = "2021"
 
+[features]
+exp-preserve-order = ["jrsonnet-evaluator/exp-preserve-order"]
+
 [dependencies]
 jrsonnet-evaluator = { path = "../../crates/jrsonnet-evaluator", version = "0.4.2", features = [
     "explaining-traces",

--- a/crates/jrsonnet-cli/src/manifest.rs
+++ b/crates/jrsonnet-cli/src/manifest.rs
@@ -43,20 +43,30 @@
 	/// `0` for hard tabs, `-1` for single line output [default: 3 for json, 2 for yaml]
 	#[clap(long)]
 	line_padding: Option<usize>,
+	/// Preserve order in object manifestification
+	#[cfg(feature = "exp-preserve-order")]
+	#[clap(long)]
+	exp_preserve_order: bool,
 }
 impl ConfigureState for ManifestOpts {
 	fn configure(&self, state: &EvaluationState) -> Result<()> {
 		if self.string {
 			state.set_manifest_format(ManifestFormat::String);
 		} else {
+			#[cfg(feature = "exp-preserve-order")]
+			let preserve_order = self.exp_preserve_order;
 			match self.format {
 				ManifestFormatName::String => state.set_manifest_format(ManifestFormat::String),
-				ManifestFormatName::Json => {
-					state.set_manifest_format(ManifestFormat::Json(self.line_padding.unwrap_or(3)))
-				}
-				ManifestFormatName::Yaml => {
-					state.set_manifest_format(ManifestFormat::Yaml(self.line_padding.unwrap_or(2)))
-				}
+				ManifestFormatName::Json => state.set_manifest_format(ManifestFormat::Json {
+					padding: self.line_padding.unwrap_or(3),
+					#[cfg(feature = "exp-preserve-order")]
+					preserve_order,
+				}),
+				ManifestFormatName::Yaml => state.set_manifest_format(ManifestFormat::Yaml {
+					padding: self.line_padding.unwrap_or(2),
+					#[cfg(feature = "exp-preserve-order")]
+					preserve_order,
+				}),
 			}
 		}
 		if self.yaml_stream {

--- a/crates/jrsonnet-evaluator/Cargo.toml
+++ b/crates/jrsonnet-evaluator/Cargo.toml
@@ -15,6 +15,10 @@
 # Allows library authors to throw custom errors
 anyhow-error = ["anyhow"]
 
+# Allows to preserve field order in objects
+exp-preserve-order = []
+exp-serde-preserve-order = ["serde_json/preserve_order"]
+
 [dependencies]
 jrsonnet-interner = { path = "../jrsonnet-interner", version = "0.4.2" }
 jrsonnet-parser = { path = "../jrsonnet-parser", version = "0.4.2" }

--- a/crates/jrsonnet-evaluator/src/builtin/manifest.rs
+++ b/crates/jrsonnet-evaluator/src/builtin/manifest.rs
@@ -21,6 +21,8 @@
 	pub mtype: ManifestType,
 	pub newline: &'s str,
 	pub key_val_sep: &'s str,
+	#[cfg(feature = "exp-preserve-order")]
+	pub preserve_order: bool,
 }
 
 pub fn manifest_json_ex(val: &Val, options: &ManifestJsonOptions<'_>) -> Result<String> {
@@ -85,7 +87,10 @@
 		Val::Obj(obj) => {
 			obj.run_assertions()?;
 			buf.push('{');
-			let fields = obj.fields();
+			let fields = obj.fields(
+				#[cfg(feature = "exp-preserve-order")]
+				options.preserve_order,
+			);
 			if !fields.is_empty() {
 				if mtype != ManifestType::ToString && mtype != ManifestType::Minify {
 					buf.push_str(options.newline);
@@ -182,6 +187,10 @@
 	/// safe_key: 1
 	/// ```
 	pub quote_keys: bool,
+	/// If true - then order of fields is preserved as written,
+	/// instead of sorting alphabetically
+	#[cfg(feature = "exp-preserve-order")]
+	pub preserve_order: bool,
 }
 
 /// From https://github.com/chyh1990/yaml-rust/blob/da52a68615f2ecdd6b7e4567019f280c433c1521/src/emitter.rs#L289
@@ -287,7 +296,14 @@
 			if o.is_empty() {
 				buf.push_str("{}");
 			} else {
-				for (i, key) in o.fields().iter().enumerate() {
+				for (i, key) in o
+					.fields(
+						#[cfg(feature = "exp-preserve-order")]
+						options.preserve_order,
+					)
+					.iter()
+					.enumerate()
+				{
 					if i != 0 {
 						buf.push('\n');
 						buf.push_str(cur_padding);

--- a/crates/jrsonnet-evaluator/src/builtin/mod.rs
+++ b/crates/jrsonnet-evaluator/src/builtin/mod.rs
@@ -162,11 +162,7 @@
 	Ok(match x {
 		A(x) => x.chars().count(),
 		B(x) => x.len(),
-		C(x) => x
-			.fields_visibility()
-			.into_iter()
-			.filter(|(_k, v)| *v)
-			.count(),
+		C(x) => x.len(),
 		D(f) => f.args_len(),
 	})
 }
@@ -191,8 +187,20 @@
 }
 
 #[jrsonnet_macros::builtin]
-fn builtin_object_fields_ex(obj: ObjValue, inc_hidden: bool) -> Result<VecVal> {
-	let out = obj.fields_ex(inc_hidden);
+fn builtin_object_fields_ex(
+	obj: ObjValue,
+	inc_hidden: bool,
+	#[cfg(feature = "exp-preserve-order")] preserve_order: Option<bool>,
+) -> Result<VecVal> {
+	#[cfg(not(feature = "exp-preserve-order"))]
+	let preserve_order = false;
+	#[cfg(feature = "exp-preserve-order")]
+	let preserve_order = preserve_order.unwrap_or(false);
+	let out = obj.fields_ex(
+		inc_hidden,
+		#[cfg(feature = "exp-preserve-order")]
+		preserve_order,
+	);
 	Ok(VecVal(Cc::new(
 		out.into_iter().map(Val::Str).collect::<Vec<_>>(),
 	)))
@@ -586,6 +594,7 @@
 	indent: IStr,
 	newline: Option<IStr>,
 	key_val_sep: Option<IStr>,
+	#[cfg(feature = "exp-preserve-order")] preserve_order: Option<bool>,
 ) -> Result<String> {
 	let newline = newline.as_deref().unwrap_or("\n");
 	let key_val_sep = key_val_sep.as_deref().unwrap_or(": ");
@@ -596,6 +605,8 @@
 			mtype: ManifestType::Std,
 			newline,
 			key_val_sep,
+			#[cfg(feature = "exp-preserve-order")]
+			preserve_order: preserve_order.unwrap_or(false),
 		},
 	)
 }
@@ -605,6 +616,7 @@
 	value: Any,
 	indent_array_in_object: Option<bool>,
 	quote_keys: Option<bool>,
+	#[cfg(feature = "exp-preserve-order")] preserve_order: Option<bool>,
 ) -> Result<String> {
 	manifest_yaml_ex(
 		&value.0,
@@ -616,6 +628,8 @@
 				""
 			},
 			quote_keys: quote_keys.unwrap_or(true),
+			#[cfg(feature = "exp-preserve-order")]
+			preserve_order: preserve_order.unwrap_or(false),
 		},
 	)
 }

--- a/crates/jrsonnet-evaluator/src/integrations/serde.rs
+++ b/crates/jrsonnet-evaluator/src/integrations/serde.rs
@@ -28,7 +28,10 @@
 			}
 			Val::Obj(o) => {
 				let mut out = Map::new();
-				for key in o.fields() {
+				for key in o.fields(
+					#[cfg(feature = "exp-preserve-order")]
+					cfg!(feature = "exp-serde-preserve-order"),
+				) {
 					out.insert(
 						(&key as &str).into(),
 						o.get(key)?

--- a/crates/jrsonnet-evaluator/src/lib.rs
+++ b/crates/jrsonnet-evaluator/src/lib.rs
@@ -100,7 +100,11 @@
 			ext_natives: Default::default(),
 			tla_vars: Default::default(),
 			import_resolver: Box::new(DummyImportResolver),
-			manifest_format: ManifestFormat::Json(4),
+			manifest_format: ManifestFormat::Json {
+				padding: 4,
+				#[cfg(feature = "exp-preserve-order")]
+				preserve_order: false,
+			},
 			trace_format: Box::new(CompactFormat {
 				padding: 4,
 				resolver: trace::PathResolver::Absolute,

--- a/crates/jrsonnet-evaluator/src/obj.rs
+++ b/crates/jrsonnet-evaluator/src/obj.rs
@@ -18,10 +18,82 @@
 	push_frame, throw, weak_ptr_eq, weak_raw, Bindable, LazyBinding, LazyVal, Result, Val,
 };
 
+#[cfg(not(feature = "exp-preserve-order"))]
+pub(crate) mod ordering {
+	use gcmodule::Trace;
+
+	#[derive(Clone, Copy, Default, Debug, Trace)]
+	pub struct FieldIndex;
+	impl FieldIndex {
+		pub fn next(self) -> Self {
+			Self
+		}
+	}
+
+	#[derive(Clone, Copy, Default, Debug, Trace)]
+	pub struct SuperDepth;
+	impl SuperDepth {
+		pub fn deeper(self) -> Self {
+			Self
+		}
+	}
+
+	#[derive(Clone, Copy)]
+	pub struct FieldSortKey;
+	impl FieldSortKey {
+		pub fn new(_: SuperDepth, _: FieldIndex) -> Self {
+			Self
+		}
+	}
+}
+
+#[cfg(feature = "exp-preserve-order")]
+mod ordering {
+	use std::cmp::Reverse;
+
+	use gcmodule::Trace;
+
+	#[derive(Clone, Copy, Default, Debug, Trace, PartialEq, Eq, PartialOrd, Ord)]
+	pub struct FieldIndex(u32);
+	impl FieldIndex {
+		pub fn next(self) -> Self {
+			Self(self.0 + 1)
+		}
+	}
+
+	#[derive(Clone, Copy, Default, PartialEq, Eq, PartialOrd, Ord, Debug)]
+	pub struct SuperDepth(u32);
+	impl SuperDepth {
+		pub fn deeper(self) -> Self {
+			Self(self.0 + 1)
+		}
+	}
+
+	#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+	pub struct FieldSortKey(Reverse<SuperDepth>, FieldIndex);
+	impl FieldSortKey {
+		pub fn new(depth: SuperDepth, index: FieldIndex) -> Self {
+			Self(Reverse(depth), index)
+		}
+		pub fn collide(self, other: Self) -> Self {
+			if self.0 .0 > other.0 .0 {
+				self
+			} else if self.0 .0 < other.0 .0 {
+				other
+			} else {
+				unreachable!("object can't have two fields with same name")
+			}
+		}
+	}
+}
+
+pub(crate) use ordering::*;
+
 #[derive(Debug, Trace)]
 pub struct ObjMember {
 	pub add: bool,
 	pub visibility: Visibility,
+	original_index: FieldIndex,
 	pub invoke: LazyBinding,
 	pub location: Option<ExprLocation>,
 }
@@ -120,6 +192,14 @@
 			),
 		}
 	}
+	pub(crate) fn extend_with_raw_member(self, key: IStr, value: ObjMember) -> Self {
+		let mut new = GcHashMap::with_capacity(1);
+		new.insert(key, value);
+		Self::new(Some(self), Cc::new(new), Cc::new(Vec::new()))
+	}
+	pub fn extend_field(&mut self, name: IStr) -> ObjMemberBuilder<ExtendBuilder> {
+		ObjMemberBuilder::new(ExtendBuilder(self), name, FieldIndex::default())
+	}
 	pub fn with_this(&self, this_obj: Self) -> Self {
 		Self(Cc::new(ObjValueInternals {
 			super_obj: self.0.super_obj.clone(),
@@ -131,6 +211,13 @@
 		}))
 	}
 
+	pub fn len(&self) -> usize {
+		self.fields_visibility()
+			.into_iter()
+			.filter(|(_, (visible, _))| *visible)
+			.count()
+	}
+
 	pub fn is_empty(&self) -> bool {
 		if !self.0.this_entries.is_empty() {
 			return false;
@@ -143,51 +230,93 @@
 	}
 
 	/// Run callback for every field found in object
-	pub(crate) fn enum_fields(&self, handler: &mut impl FnMut(&IStr, &ObjMember) -> bool) -> bool {
+	pub(crate) fn enum_fields(
+		&self,
+		depth: SuperDepth,
+		handler: &mut impl FnMut(SuperDepth, &IStr, &ObjMember) -> bool,
+	) -> bool {
 		if let Some(s) = &self.0.super_obj {
-			if s.enum_fields(handler) {
+			if s.enum_fields(depth.deeper(), handler) {
 				return true;
 			}
 		}
 		for (name, member) in self.0.this_entries.iter() {
-			if handler(name, member) {
+			if handler(depth, name, member) {
 				return true;
 			}
 		}
 		false
 	}
 
-	pub fn fields_visibility(&self) -> FxHashMap<IStr, bool> {
+	pub fn fields_visibility(&self) -> FxHashMap<IStr, (bool, FieldSortKey)> {
 		let mut out = FxHashMap::default();
-		self.enum_fields(&mut |name, member| {
+		self.enum_fields(SuperDepth::default(), &mut |depth, name, member| {
+			let new_sort_key = FieldSortKey::new(depth, member.original_index);
 			match member.visibility {
 				Visibility::Normal => {
 					let entry = out.entry(name.to_owned());
-					entry.or_insert(true);
+					let v = entry.or_insert((true, new_sort_key));
+					v.1 = new_sort_key;
 				}
 				Visibility::Hidden => {
-					out.insert(name.to_owned(), false);
+					out.insert(name.to_owned(), (false, new_sort_key));
 				}
 				Visibility::Unhide => {
-					out.insert(name.to_owned(), true);
+					out.insert(name.to_owned(), (true, new_sort_key));
 				}
 			};
 			false
 		});
 		out
 	}
-	pub fn fields_ex(&self, include_hidden: bool) -> Vec<IStr> {
+	pub fn fields_ex(
+		&self,
+		include_hidden: bool,
+		#[cfg(feature = "exp-preserve-order")] preserve_order: bool,
+	) -> Vec<IStr> {
+		#[cfg(feature = "exp-preserve-order")]
+		if preserve_order {
+			let (mut fields, mut keys): (Vec<_>, Vec<_>) = self
+				.fields_visibility()
+				.into_iter()
+				.filter(|(_, (visible, _))| include_hidden || *visible)
+				.enumerate()
+				.map(|(idx, (k, (_, sk)))| (k, (sk, idx)))
+				.unzip();
+			keys.sort_unstable_by_key(|v| v.0);
+			// Reorder in-place by resulting indexes
+			for i in 0..fields.len() {
+				let x = fields[i].clone();
+				let mut j = i;
+				loop {
+					let k = keys[j].1;
+					keys[j].1 = j;
+					if k == i {
+						break;
+					}
+					fields[j] = fields[k].clone();
+					j = k
+				}
+				fields[j] = x;
+			}
+			return fields;
+		}
+
 		let mut fields: Vec<_> = self
 			.fields_visibility()
 			.into_iter()
-			.filter(|(_k, v)| include_hidden || *v)
+			.filter(|(_, (visible, _))| include_hidden || *visible)
 			.map(|(k, _)| k)
 			.collect();
 		fields.sort_unstable();
 		fields
 	}
-	pub fn fields(&self) -> Vec<IStr> {
-		self.fields_ex(false)
+	pub fn fields(&self, #[cfg(feature = "exp-preserve-order")] preserve_order: bool) -> Vec<IStr> {
+		self.fields_ex(
+			false,
+			#[cfg(feature = "exp-preserve-order")]
+			preserve_order,
+		)
 	}
 
 	pub fn field_visibility(&self, name: IStr) -> Option<Visibility> {
@@ -236,11 +365,7 @@
 		self.get_raw(key, self.0.this_obj.as_ref())
 	}
 
-	pub fn extend_with_field(self, key: IStr, value: ObjMember) -> Self {
-		let mut new = GcHashMap::with_capacity(1);
-		new.insert(key, value);
-		Self::new(Some(self), Cc::new(new), Cc::new(Vec::new()))
-	}
+	// pub fn extend_with(self, key: )
 
 	fn get_raw(&self, key: IStr, real_this: Option<&Self>) -> Result<Option<Val>> {
 		let real_this = real_this.unwrap_or(self);
@@ -339,6 +464,7 @@
 	super_obj: Option<ObjValue>,
 	map: GcHashMap<IStr, ObjMember>,
 	assertions: Vec<TraceBox<dyn ObjectAssertion>>,
+	next_field_index: FieldIndex,
 }
 impl ObjValueBuilder {
 	pub fn new() -> Self {
@@ -349,6 +475,7 @@
 			super_obj: None,
 			map: GcHashMap::with_capacity(capacity),
 			assertions: Vec::new(),
+			next_field_index: FieldIndex::default(),
 		}
 	}
 	pub fn reserve_asserts(&mut self, capacity: usize) -> &mut Self {
@@ -364,14 +491,10 @@
 		self.assertions.push(assertion);
 		self
 	}
-	pub fn member(&mut self, name: IStr) -> ObjMemberBuilder {
-		ObjMemberBuilder {
-			value: self,
-			name,
-			add: false,
-			visibility: Visibility::Normal,
-			location: None,
-		}
+	pub fn member(&mut self, name: IStr) -> ObjMemberBuilder<ValueBuilder> {
+		let field_index = self.next_field_index;
+		self.next_field_index = self.next_field_index.next();
+		ObjMemberBuilder::new(ValueBuilder(self), name, field_index)
 	}
 
 	pub fn build(self) -> ObjValue {
@@ -385,16 +508,28 @@
 }
 
 #[must_use = "value not added unless binding() was called"]
-pub struct ObjMemberBuilder<'v> {
-	value: &'v mut ObjValueBuilder,
+pub struct ObjMemberBuilder<Kind> {
+	kind: Kind,
 	name: IStr,
 	add: bool,
 	visibility: Visibility,
+	original_index: FieldIndex,
 	location: Option<ExprLocation>,
 }
 
 #[allow(clippy::missing_const_for_fn)]
-impl<'v> ObjMemberBuilder<'v> {
+impl<Kind> ObjMemberBuilder<Kind> {
+	pub(crate) fn new(kind: Kind, name: IStr, original_index: FieldIndex) -> Self {
+		Self {
+			kind,
+			name,
+			original_index,
+			add: false,
+			visibility: Visibility::Normal,
+			location: None,
+		}
+	}
+
 	pub const fn with_add(mut self, add: bool) -> Self {
 		self.add = add;
 		self
@@ -413,6 +548,23 @@
 		self.location = Some(location);
 		self
 	}
+	fn build_member(self, binding: LazyBinding) -> (Kind, IStr, ObjMember) {
+		(
+			self.kind,
+			self.name,
+			ObjMember {
+				add: self.add,
+				visibility: self.visibility,
+				original_index: self.original_index,
+				invoke: binding,
+				location: self.location,
+			},
+		)
+	}
+}
+
+pub struct ValueBuilder<'v>(&'v mut ObjValueBuilder);
+impl<'v> ObjMemberBuilder<ValueBuilder<'v>> {
 	pub fn value(self, value: Val) -> Result<()> {
 		self.binding(LazyBinding::Bound(LazyVal::new_resolved(value)))
 	}
@@ -420,22 +572,31 @@
 		self.binding(LazyBinding::Bindable(Cc::new(bindable)))
 	}
 	pub fn binding(self, binding: LazyBinding) -> Result<()> {
-		let old = self.value.map.insert(
-			self.name.clone(),
-			ObjMember {
-				add: self.add,
-				visibility: self.visibility,
-				invoke: binding,
-				location: self.location.clone(),
-			},
-		);
+		let (receiver, name, member) = self.build_member(binding);
+		let location = member.location.clone();
+		let old = receiver.0.map.insert(name.clone(), member);
 		if old.is_some() {
 			push_frame(
-				CallLocation(self.location.as_ref()),
-				|| format!("field <{}> initializtion", self.name.clone()),
-				|| throw!(DuplicateFieldName(self.name.clone())),
+				CallLocation(location.as_ref()),
+				|| format!("field <{}> initializtion", name.clone()),
+				|| throw!(DuplicateFieldName(name.clone())),
 			)?
 		}
 		Ok(())
 	}
 }
+
+pub struct ExtendBuilder<'v>(&'v mut ObjValue);
+impl<'v> ObjMemberBuilder<ExtendBuilder<'v>> {
+	pub fn value(self, value: Val) {
+		self.binding(LazyBinding::Bound(LazyVal::new_resolved(value)))
+	}
+	pub fn bindable(self, bindable: TraceBox<dyn Bindable>) {
+		self.binding(LazyBinding::Bindable(Cc::new(bindable)))
+	}
+	pub fn binding(self, binding: LazyBinding) -> () {
+		let (receiver, name, member) = self.build_member(binding);
+		let new = receiver.0.clone();
+		*receiver.0 = new.extend_with_raw_member(name, member)
+	}
+}

--- a/crates/jrsonnet-evaluator/src/val.rs
+++ b/crates/jrsonnet-evaluator/src/val.rs
@@ -167,11 +167,31 @@
 #[derive(Clone)]
 pub enum ManifestFormat {
 	YamlStream(Box<ManifestFormat>),
-	Yaml(usize),
-	Json(usize),
+	Yaml {
+		padding: usize,
+		#[cfg(feature = "exp-preserve-order")]
+		preserve_order: bool,
+	},
+	Json {
+		padding: usize,
+		#[cfg(feature = "exp-preserve-order")]
+		preserve_order: bool,
+	},
 	ToString,
 	String,
 }
+impl ManifestFormat {
+	#[cfg(feature = "exp-preserve-order")]
+	fn preserve_order(&self) -> bool {
+		match self {
+			ManifestFormat::YamlStream(s) => s.preserve_order(),
+			ManifestFormat::Yaml { preserve_order, .. } => *preserve_order,
+			ManifestFormat::Json { preserve_order, .. } => *preserve_order,
+			ManifestFormat::ToString => false,
+			ManifestFormat::String => false,
+		}
+	}
+}
 
 #[derive(Debug, Clone, Trace)]
 pub struct Slice {
@@ -559,6 +579,8 @@
 					mtype: ManifestType::ToString,
 					newline: "\n",
 					key_val_sep: ": ",
+					#[cfg(feature = "exp-preserve-order")]
+					preserve_order: false,
 				},
 			)?
 			.into(),
@@ -571,7 +593,10 @@
 			Self::Obj(obj) => obj,
 			_ => throw!(MultiManifestOutputIsNotAObject),
 		};
-		let keys = obj.fields();
+		let keys = obj.fields(
+			#[cfg(feature = "exp-preserve-order")]
+			ty.preserve_order(),
+		);
 		let mut out = Vec::with_capacity(keys.len());
 		for key in keys {
 			let value = obj
@@ -622,8 +647,24 @@
 
 				out.into()
 			}
-			ManifestFormat::Yaml(padding) => self.to_yaml(*padding)?,
-			ManifestFormat::Json(padding) => self.to_json(*padding)?,
+			ManifestFormat::Yaml {
+				padding,
+				#[cfg(feature = "exp-preserve-order")]
+				preserve_order,
+			} => self.to_yaml(
+				*padding,
+				#[cfg(feature = "exp-preserve-order")]
+				*preserve_order,
+			)?,
+			ManifestFormat::Json {
+				padding,
+				#[cfg(feature = "exp-preserve-order")]
+				preserve_order,
+			} => self.to_json(
+				*padding,
+				#[cfg(feature = "exp-preserve-order")]
+				*preserve_order,
+			)?,
 			ManifestFormat::ToString => self.to_string()?,
 			ManifestFormat::String => match self {
 				Self::Str(s) => s.clone(),
@@ -633,7 +674,11 @@
 	}
 
 	/// For manifestification
-	pub fn to_json(&self, padding: usize) -> Result<IStr> {
+	pub fn to_json(
+		&self,
+		padding: usize,
+		#[cfg(feature = "exp-preserve-order")] preserve_order: bool,
+	) -> Result<IStr> {
 		manifest_json_ex(
 			self,
 			&ManifestJsonOptions {
@@ -645,13 +690,19 @@
 				},
 				newline: "\n",
 				key_val_sep: ": ",
+				#[cfg(feature = "exp-preserve-order")]
+				preserve_order,
 			},
 		)
 		.map(|s| s.into())
 	}
 
 	/// Calls `std.manifestJson`
-	pub fn to_std_json(&self, padding: usize) -> Result<Rc<str>> {
+	pub fn to_std_json(
+		&self,
+		padding: usize,
+		#[cfg(feature = "exp-preserve-order")] preserve_order: bool,
+	) -> Result<Rc<str>> {
 		manifest_json_ex(
 			self,
 			&ManifestJsonOptions {
@@ -659,12 +710,18 @@
 				mtype: ManifestType::Std,
 				newline: "\n",
 				key_val_sep: ": ",
+				#[cfg(feature = "exp-preserve-order")]
+				preserve_order,
 			},
 		)
 		.map(|s| s.into())
 	}
 
-	pub fn to_yaml(&self, padding: usize) -> Result<IStr> {
+	pub fn to_yaml(
+		&self,
+		padding: usize,
+		#[cfg(feature = "exp-preserve-order")] preserve_order: bool,
+	) -> Result<IStr> {
 		let padding = &" ".repeat(padding);
 		manifest_yaml_ex(
 			self,
@@ -672,6 +729,8 @@
 				padding,
 				arr_element_padding: padding,
 				quote_keys: false,
+				#[cfg(feature = "exp-preserve-order")]
+				preserve_order,
 			},
 		)
 		.map(|s| s.into())
@@ -733,8 +792,15 @@
 			if ObjValue::ptr_eq(a, b) {
 				return Ok(true);
 			}
-			let fields = a.fields();
-			if fields != b.fields() {
+			let fields = a.fields(
+				#[cfg(feature = "exp-preserve-order")]
+				false,
+			);
+			if fields
+				!= b.fields(
+					#[cfg(feature = "exp-preserve-order")]
+					false,
+				) {
 				return Ok(false);
 			}
 			for field in fields {