refactor(value): migrate Value::Object to Object storage abstraction

Builds on #57. Swap Value::Object's payload from Rc<BTreeMap<Value, Value>>
to Rc<Object> and migrate all call sites to the Object API.

as_object / as_object_mut keep their names but return &Object / &mut Object.
The mutable accessor handles Rc::make_mut internally, so callers no longer
do it themselves. Object grows into_value() and From<Object> for Value.
Value's serializer now delegates to Object::serialize, dropping a duplicate
non-string-key stringification path.

RVM IterationState::Object is rewritten around ObjectCursor: O(log n)
steps over a shared Rc<Object>, no eager pair snapshot. Snapshot
independence is preserved by Rc copy-on-write; setup_next_iteration
advances the cursor inline and advance() becomes a no-op for this variant.
A new iteration_state_object_is_snapshot_independent_of_source test
covers CoW against a mutated alias.

Value::Set still wraps Rc<BTreeSet<Value>>; the matching Set abstraction
and its swap ship in follow-up PRs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: anakrish

src/builtins/azure_policy/helpers.rs

@@ -319,7 +319,7 @@ pub fn resolve_path(root: &Value, path: &str) -> Value {
         match &current {
             Value::Object(map) => {
                 let mut next = None;
-                for (key, value) in map.iter() {
+                for (key, value) in map.iter_sorted() {
                     if let Value::String(ref key_str) = *key {
                         if strings::keys::eq(key_str, &segment) {
                             next = Some(value.clone());

src/builtins/azure_policy/template_functions_collection.rs

@@ -8,10 +8,10 @@
 use crate::ast::{Expr, Ref};
 use crate::builtins;
 use crate::lexer::Span;
+use crate::value::Object;
 use crate::value::Value;
 use crate::Rc;
 
-use alloc::collections::BTreeMap;
 use alloc::vec::Vec;
 use anyhow::Result;
 
@@ -72,7 +72,7 @@ fn fn_intersection(
             // Intersection of objects: keep key-value pairs from the first
             // object only when the key exists in every other object AND
             // the value is equal across all of them.
-            let mut result: BTreeMap<Value, Value> = first.as_ref().clone();
+            let mut result: Object = first.as_ref().clone();
             for arg in rest {
                 let Value::Object(ref other) = *arg else {
                     return Ok(Value::Undefined);
@@ -114,7 +114,7 @@ fn fn_union(_span: &Span, _params: &[Ref<Expr>], args: &[Value], _strict: bool)
         Value::Object(_) => {
             // Union of objects: recursive merge. Nested objects are merged
             // recursively; all other types (including arrays) use last-writer-wins.
-            let mut result = BTreeMap::<Value, Value>::new();
+            let mut result = Object::new();
             for arg in args {
                 let Value::Object(ref obj) = *arg else {
                     return Ok(Value::Undefined);
@@ -264,7 +264,7 @@ fn fn_create_object(
         );
     }
 
-    let mut map = BTreeMap::<Value, Value>::new();
+    let mut map = Object::new();
 
     for pair in args.chunks(2) {
         #[allow(clippy::pattern_type_mismatch)]
@@ -280,9 +280,9 @@ fn fn_create_object(
 
 /// Recursively merge two objects.  Nested objects are merged; everything
 /// else (including arrays) uses the value from `incoming`.
-fn merge_objects(base: &BTreeMap<Value, Value>, overlay: &BTreeMap<Value, Value>) -> Value {
+fn merge_objects(base: &Object, overlay: &Object) -> Value {
     let mut result = base.clone();
-    for (k, v) in overlay {
+    for (k, v) in overlay.iter() {
         #[allow(clippy::needless_borrowed_reference)]
         let merged = match (result.get(k), v) {
             (Some(&Value::Object(ref prev)), &Value::Object(ref next)) => merge_objects(prev, next),

src/builtins/azure_policy/template_functions_misc.rs

@@ -8,10 +8,10 @@
 use crate::ast::{Expr, Ref};
 use crate::builtins;
 use crate::lexer::Span;
+use crate::value::Object;
 use crate::value::Value;
 use crate::Rc;
 
-use alloc::collections::BTreeMap;
 use alloc::string::{String, ToString as _};
 use alloc::vec::Vec;
 use anyhow::Result;
@@ -84,8 +84,8 @@ fn fn_items(_span: &Span, _params: &[Ref<Expr>], args: &[Value], _strict: bool)
         return Ok(Value::Undefined);
     };
     let mut result = Vec::with_capacity(obj.len());
-    for (k, v) in obj.as_ref() {
-        let mut entry = BTreeMap::<Value, Value>::new();
+    for (k, v) in obj.iter_sorted() {
+        let mut entry = Object::new();
         entry.insert(Value::from("key"), k.clone());
         entry.insert(Value::from("value"), v.clone());
         result.push(Value::Object(Rc::new(entry)));

src/builtins/encoding.rs

@@ -308,7 +308,7 @@ fn urlquery_encode_object(
 
     {
         let mut pairs = url.query_pairs_mut();
-        for (key, value) in obj.iter() {
+        for (key, value) in obj.iter_sorted() {
             let key = ensure_string(name, &params[0], key)?;
             match value {
                 Value::String(v) => {

src/builtins/graph.rs

@@ -7,10 +7,11 @@ use crate::ast::{Expr, Ref};
 use crate::builtins;
 use crate::builtins::utils::{enforce_limit, ensure_args_count, ensure_object};
 use crate::lexer::Span;
+use crate::value::Object;
 use crate::value::Value;
 use crate::*;
 
-use alloc::collections::{BTreeMap, BTreeSet};
+use alloc::collections::BTreeSet;
 
 use anyhow::{bail, Result};
 
@@ -80,7 +81,7 @@ fn reachable(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) ->
 }
 
 fn visit(
-    graph: &BTreeMap<Value, Value>,
+    graph: &Object,
     visited: &mut BTreeSet<Value>,
     node: &Value,
     path: &mut Vec<Value>,
@@ -211,7 +212,7 @@ fn walk_visit(path: &mut Vec<Value>, value: &Value, paths: &mut Vec<Value>) -> R
             }
         }
         Value::Object(obj) => {
-            for (key, value) in obj.iter() {
+            for (key, value) in obj.iter_sorted() {
                 path.push(key.clone());
                 // Guard path stack growth while traversing object entries.
                 enforce_limit()?;

src/builtins/objects.rs

@@ -205,7 +205,7 @@ fn merge_filters(
                     let vref = match f {
                         Value::Object(obj) => {
                             let obj = Rc::make_mut(obj);
-                            let entry = obj.entry(p.clone()).or_insert_with(Value::new_object);
+                            let entry = obj.get_or_insert_with(p.clone(), Value::new_object);
                             // Guard filter map growth when creating nested objects.
                             enforce_limit()?;
                             entry

src/builtins/strings.rs

@@ -207,7 +207,7 @@ fn to_string(v: &Value, unescape: bool) -> String {
         }
         Value::Object(o) => {
             "{".to_owned()
-                + &o.iter()
+                + &o.iter_sorted()
                     .map(|(k, v)| to_string(k, true) + ": " + &to_string(v, true))
                     .collect::<Vec<String>>()
                     .join(", ")
@@ -568,7 +568,7 @@ fn replace_n(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -
     let mut s = ensure_string(name, &params[1], &args[1])?;
 
     let span = params[0].span();
-    for item in obj.as_ref().iter() {
+    for item in obj.as_ref().iter_sorted() {
         match item {
             (Value::String(k), Value::String(v)) => {
                 s = s.replace(k.as_ref(), v.as_ref()).into();

src/builtins/utils.rs

@@ -5,11 +5,12 @@
 use crate::ast::{Expr, Ref};
 use crate::lexer::Span;
 use crate::number::Number;
+use crate::value::Object;
 use crate::Rc;
 use crate::Value;
 use crate::*;
 
-use alloc::collections::{BTreeMap, BTreeSet};
+use alloc::collections::BTreeSet;
 
 use anyhow::{bail, Result};
 
@@ -168,7 +169,7 @@ pub fn ensure_set(fcn: &str, arg: &Expr, v: Value) -> Result<Rc<BTreeSet<Value>>
     })
 }
 
-pub fn ensure_object(fcn: &str, arg: &Expr, v: Value) -> Result<Rc<BTreeMap<Value, Value>>> {
+pub fn ensure_object(fcn: &str, arg: &Expr, v: Value) -> Result<Rc<Object>> {
     Ok(match v {
         Value::Object(o) => o,
         _ => {

src/interpreter.rs

@@ -28,7 +28,6 @@ use crate::{Expression, Extension, Location, QueryResult, QueryResults};
 use crate::query::traversal::traverse;
 
 use crate::Rc;
-use alloc::collections::btree_map::Entry as BTreeMapEntry;
 use alloc::collections::{BTreeMap, BTreeSet};
 use anyhow::{anyhow, bail, Result};
 use core::ops::Bound::*;
@@ -1312,10 +1311,10 @@ impl Interpreter {
                                 *obj = Value::new_object();
                             }
 
-                            obj = obj
-                                .as_object_mut()?
-                                .entry(Value::String(p.to_string().into()))
-                                .or_insert(Value::new_object());
+                            obj = obj.as_object_mut()?.get_or_insert_with(
+                                Value::String(p.to_string().into()),
+                                Value::new_object,
+                            );
                         }
                         *obj = value;
                         // Mark modified rules as processed.
@@ -1682,29 +1681,21 @@ impl Interpreter {
                     let set = obj
                         .as_object_mut()
                         .map_err(|_| anyhow!(span.error("previous value is not an object")))?
-                        .entry(p)
-                        .or_insert(Value::new_set())
+                        .get_or_insert_with(p, Value::new_set)
                         .as_set_mut()
                         .map_err(|_| anyhow!(span.error("previous value is not a set")))?;
                     set.append(value.as_set_mut()?);
                 } else {
                     let obj = obj
                         .as_object_mut()
                         .map_err(|_| anyhow!(span.error("previous value is not an object")))?;
-                    match obj.entry(p) {
-                        BTreeMapEntry::Vacant(v) => {
-                            if value != Value::Undefined {
-                                v.insert(value);
-                            } else {
-                                // TODO: clean this assumption between Undefined vs Object.
-                                v.insert(Value::new_object());
-                            }
-                        }
-                        BTreeMapEntry::Occupied(o) => {
-                            if o.get() != &value && value != Value::Undefined {
-                                bail!(span
-                                    .error("complete rules should not produce multiple outputs"))
-                            }
+                    if value == Value::Undefined {
+                        // TODO: clean this assumption between Undefined vs Object.
+                        obj.get_or_insert_with(p, Value::new_object);
+                    } else {
+                        let existing = obj.get_or_insert_with(p, || value.clone());
+                        if *existing != value {
+                            bail!(span.error("complete rules should not produce multiple outputs"))
                         }
                     }
                 }
@@ -1713,8 +1704,7 @@ impl Interpreter {
                 obj = obj
                     .as_object_mut()
                     .map_err(|_| anyhow!(span.error("previous value is not an object")))?
-                    .entry(p)
-                    .or_insert(Value::new_object());
+                    .get_or_insert_with(p, Value::new_object);
             }
         }
         Ok(())
@@ -1822,8 +1812,7 @@ impl Interpreter {
                     let set = ctx_mut
                         .rule_value
                         .as_object_mut()?
-                        .entry(Value::from_array(comps))
-                        .or_insert(Value::new_set());
+                        .get_or_insert_with(Value::from_array(comps), Value::new_set);
                     if output != Value::Undefined {
                         set.as_set_mut()?.insert(output);
                         return Ok(true);
@@ -1832,20 +1821,13 @@ impl Interpreter {
                 }
 
                 // Non-set rule.
-                match ctx_mut
-                    .rule_value
-                    .as_object_mut()?
-                    .entry(Value::from_array(comps))
-                {
-                    BTreeMapEntry::Vacant(v) => {
-                        v.insert(output);
-                    }
-                    BTreeMapEntry::Occupied(o) if o.get() != &output => bail!(rule_ref
+                let key = Value::from_array(comps);
+                let obj_mut = ctx_mut.rule_value.as_object_mut()?;
+                let existing = obj_mut.get_or_insert_with(key, || output.clone());
+                if *existing != output {
+                    bail!(rule_ref
                         .span()
-                        .error("rules must not produce multiple outputs")),
-                    _ => {
-                        // Rule produced same value.
-                    }
+                        .error("rules must not produce multiple outputs"));
                 }
 
                 return Ok(true);
@@ -2471,7 +2453,7 @@ impl Interpreter {
             }
             Value::Object(map) => {
                 s.push('{');
-                for (idx, (k, entry_value)) in map.iter().enumerate() {
+                for (idx, (k, entry_value)) in map.iter_sorted().enumerate() {
                     if idx > 0 {
                         s.push_str(", ");
                     }

src/languages/azure_policy/aliases/denormalizer/mod.rs

@@ -213,10 +213,10 @@ pub fn denormalize_with_aliases(
     // Phase 4: Attach properties to result.
     if !properties.is_empty() {
         if let Some(Value::Object(existing_rc)) = result.get_mut("properties") {
-            // Merge directly into the BTreeMap, avoiding full ObjMap round-trip.
+            // Merge directly into the Object, avoiding full ObjMap round-trip.
             let existing = Rc::make_mut(existing_rc);
             for (k, v) in properties {
-                existing.entry(Value::String(k)).or_insert(v);
+                existing.get_or_insert_with(Value::String(k), || v);
             }
         } else {
             obj_insert(&mut result, "properties", make_value(properties));