refactor(azure_policy): reduce AliasRegistry allocations via Rc sharing (#725)

Replace the compiler's two cloned BTreeMap fields (alias_map and
alias_modifiable) with a single Option<Rc<AliasRegistry>>. This
eliminates cloning two 73K-entry maps on every compilation by sharing
the registry through a reference-counted pointer.

Additional improvements:
- alias_map()/alias_modifiable_map() return &BTreeMap (zero-copy)
- Safe .get() indexing in ingest_alias_entries and build_object_from_keys
- Null-tolerant deserialization for AliasEntry.paths (~97% of real
  Azure catalog entries emit "paths": null)

All changes are within the azure_policy feature gate.

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

examples/regorus/azure_policy.rs

@@ -23,8 +23,7 @@ use regorus::languages::azure_policy::aliases::AliasRegistry;
 use regorus::languages::azure_policy::compiler;
 use regorus::languages::azure_policy::parser;
 use regorus::rvm::RegoVM;
-use regorus::Source;
+use regorus::{Rc, Source, Value};
-use regorus::Value;
 
 /// Evaluate an Azure Policy definition against a resource.
 ///
@@ -60,11 +59,8 @@ pub fn azure_policy_eval(
     println!("Parsed policy definition from {policy_definition}");
 
     // 3. Compile to RVM bytecode.
-    let program = compiler::compile_policy_definition_with_aliases(
+    let registry = Rc::new(registry);
-        &defn,
+    let program = compiler::compile_policy_definition_with_aliases(&defn, Rc::clone(&registry))?;
-        registry.alias_map(),
-        registry.alias_modifiable_map(),
-    )?;
     println!("Compiled policy to RVM bytecode");
 
     // 4. Build normalized input.
@@ -138,7 +134,7 @@ pub fn azure_policy_aliases(aliases: String, resource_type: Option<String>) -> R
     if let Some(ref rt) = resource_type {
         let rt_lower = rt.to_lowercase();
         let mut found = false;
-        for (alias_name, _) in registry.alias_map() {
+        for alias_name in registry.alias_map().keys() {
             if alias_name.to_lowercase().starts_with(&rt_lower) {
                 println!("  {alias_name}");
                 found = true;
@@ -148,7 +144,7 @@ pub fn azure_policy_aliases(aliases: String, resource_type: Option<String>) -> R
             bail!("no aliases found for resource type '{rt}'");
         }
     } else {
-        for (alias_name, _) in registry.alias_map() {
+        for alias_name in registry.alias_map().keys() {
             println!("  {alias_name}");
         }
     }

src/languages/azure_policy/aliases/mod.rs

@@ -172,11 +172,31 @@ impl AliasRegistry {
         let prefix = alloc::format!("{}/", fq_type);
 
         for alias in aliases {
+            // Skip aliases without a default_path — the normalizer's
+            // resolve_resource_type also skips these, so inserting them into
+            // compiler maps would cause a divergence where the compiler
+            // resolves the alias but normalized input never contains the field.
+            if alias.default_path.is_none() {
+                continue;
+            }
+
             // Derive the short name by stripping the resource type prefix.
             let raw_short = if alias.name.len() > prefix.len()
-                && alias.name[..prefix.len()].eq_ignore_ascii_case(&prefix)
+                && alias
+                    .name
+                    .get(..prefix.len())
+                    .is_some_and(|s| s.eq_ignore_ascii_case(&prefix))
             {
-                alias.name[prefix.len()..].to_string()
+                // Both slice boundaries are valid: prefix is ASCII
+                // (resource type + '/'), so if `..prefix.len()` succeeded
+                // above, `prefix.len()..` is guaranteed to be on a char
+                // boundary too.  The `unwrap_or` is a defensive fallback
+                // that can never trigger for well-formed Azure alias names.
+                alias
+                    .name
+                    .get(prefix.len()..)
+                    .unwrap_or(&alias.name)
+                    .to_string()
             } else if let Some(rest) = alias
                 .name
                 .rfind('/')
@@ -260,20 +280,19 @@ impl AliasRegistry {
             .map(String::as_str)
     }
 
-    /// Return a clone of the alias-to-short-name map for use by the compiler.
+    /// Return a reference to the alias-to-short-name map.
     ///
-    /// The compiler stores this map internally so it can resolve fully-qualified
+    /// Keys are lowercase fully-qualified alias names; values are short names.
-    /// alias names without holding a reference to the registry.
+    pub const fn alias_map(&self) -> &BTreeMap<String, String> {
-    pub fn alias_map(&self) -> BTreeMap<String, String> {
+        &self.alias_to_short
-        self.alias_to_short.clone()
     }
 
-    /// Return a clone of the alias-to-modifiable map for use by the compiler.
+    /// Return a reference to the alias-to-modifiable map.
     ///
-    /// Maps lowercase fully-qualified alias names to `true` when the alias
+    /// Keys are lowercase fully-qualified alias names; values are `true` when
-    /// has `defaultMetadata.attributes = "Modifiable"`.
+    /// the alias has `defaultMetadata.attributes = "Modifiable"`.
-    pub fn alias_modifiable_map(&self) -> BTreeMap<String, bool> {
+    pub const fn alias_modifiable_map(&self) -> &BTreeMap<String, bool> {
-        self.alias_modifiable.clone()
+        &self.alias_modifiable
     }
 
     /// Normalize a raw ARM resource and wrap it in the input envelope.

src/languages/azure_policy/aliases/types.rs

@@ -20,6 +20,20 @@ use serde::{Deserialize, Deserializer};
 
 use crate::Rc;
 
+// ---------------------------------------------------------------------------
+// Deserialization helpers
+// ---------------------------------------------------------------------------
+
+/// Deserialize a `Vec<T>` that tolerates JSON `null` by mapping it to an
+/// empty vector.
+fn deserialize_null_as_empty_vec<'de, T, D>(deserializer: D) -> Result<Vec<T>, D::Error>
+where
+    T: Deserialize<'de>,
+    D: Deserializer<'de>,
+{
+    Ok(Option::<Vec<T>>::deserialize(deserializer)?.unwrap_or_default())
+}
+
 // ─── Top-level response wrappers ────────────────────────────────────────────
 
 /// ARM API response envelope: `{ "value": [...] }`
@@ -100,7 +114,10 @@ pub struct AliasEntry {
 
     /// Versioned path entries.  Empty for the vast majority of aliases that
     /// have only a `defaultPath`.
-    #[serde(default)]
+    ///
+    /// In real Azure catalog data (~97% of aliases), `az provider list` emits
+    /// `"paths": null` rather than an empty array.
+    #[serde(default, deserialize_with = "deserialize_null_as_empty_vec")]
     pub paths: Vec<AliasPath>,
 }
 

src/languages/azure_policy/compiler/core.rs

@@ -18,6 +18,7 @@ use crate::rvm::program::{Program, SpanInfo};
 use crate::rvm::Instruction;
 use crate::{Rc, Value};
 
+use crate::languages::azure_policy::aliases::AliasRegistry;
 use crate::languages::azure_policy::ast::PolicyRule;
 
 // ---------------------------------------------------------------------------
@@ -44,10 +45,9 @@ pub(super) struct Compiler {
     pub(super) cached_input_reg: Option<u8>,
     /// Cached register for `LoadContext` — allocated once on first use.
     pub(super) cached_context_reg: Option<u8>,
-    /// Map from lowercase fully-qualified alias name → short name.
+    /// Alias registry for resolving fully-qualified alias names.
-    pub(super) alias_map: BTreeMap<String, String>,
+    /// Shared via `Rc` to avoid cloning the 73K-entry alias maps.
-    /// Map from lowercase fully-qualified alias name → modifiable flag.
+    pub(super) alias_registry: Option<Rc<AliasRegistry>>,
-    pub(super) alias_modifiable: BTreeMap<String, bool>,
     /// Default values for policy parameters.
     pub(super) parameter_defaults: Option<Value>,
     /// Cached literal-table index for `parameter_defaults` (or an empty object
@@ -338,8 +338,13 @@ impl Compiler {
         path: &str,
         span: &crate::lexer::Span,
     ) -> Result<String> {
+        let alias_map = match &self.alias_registry {
+            Some(reg) => reg.alias_map(),
+            None => return Ok(path.to_string()),
+        };
+
         let lc = path.to_ascii_lowercase();
-        if let Some(short) = self.alias_map.get(&lc) {
+        if let Some(short) = alias_map.get(&lc) {
             let resolved = short.clone();
             let result = Self::strip_fq_prefix(&resolved).to_ascii_lowercase();
             return Ok(result);
@@ -348,7 +353,7 @@ impl Compiler {
         // Fallback: derive array path from a corresponding `[*]` alias.
         if !lc.contains("[*]") {
             let wildcard_key = alloc::format!("{}[*]", lc);
-            if let Some(short) = self.alias_map.get(&wildcard_key) {
+            if let Some(short) = alias_map.get(&wildcard_key) {
                 let resolved = Self::strip_fq_prefix(short).to_ascii_lowercase();
                 if let Some(base) = resolved.strip_suffix("[*]") {
                     return Ok(base.to_string());
@@ -356,14 +361,14 @@ impl Compiler {
             }
         }
 
-        if !self.alias_map.is_empty() && !self.alias_fallback_to_raw {
+        if !alias_map.is_empty() && !self.alias_fallback_to_raw {
             bail!(span.error(&alloc::format!(
                 "unknown alias '{}': field references must use fully-qualified alias names when an alias catalog is loaded",
                 path
             )));
         }
 
-        if self.alias_map.is_empty() {
+        if alias_map.is_empty() {
             Ok(path.to_string())
         } else {
             let result = Self::strip_fq_prefix(path).to_ascii_lowercase();

src/languages/azure_policy/compiler/count.rs

@@ -998,7 +998,13 @@ impl Compiler {
                     return Ok(result);
                 }
             }
-            Err(e) if !self.alias_map.is_empty() && !self.alias_fallback_to_raw => {
+            Err(e)
+                if self
+                    .alias_registry
+                    .as_ref()
+                    .is_some_and(|r| !r.alias_map().is_empty())
+                    && !self.alias_fallback_to_raw =>
+            {
                 return Err(e);
             }
             _ => {}

src/languages/azure_policy/compiler/effects.rs

@@ -692,13 +692,18 @@ impl Compiler {
         field_path: &str,
         span: &crate::lexer::Span,
     ) -> Result<()> {
-        if self.alias_modifiable.is_empty() {
+        let modifiable_map = match &self.alias_registry {
+            Some(reg) => reg.alias_modifiable_map(),
+            None => return Ok(()),
+        };
+
+        if modifiable_map.is_empty() {
             return Ok(());
         }
 
         let lc = field_path.to_lowercase();
 
-        if let Some(&modifiable) = self.alias_modifiable.get(&lc) {
+        if let Some(&modifiable) = modifiable_map.get(&lc) {
             if !modifiable {
                 bail!(span.error(&format!(
                     "alias '{}' is not modifiable (defaultMetadata.attributes != 'Modifiable')",
@@ -803,7 +808,6 @@ fn unescape_arm_literal(s: &str) -> alloc::string::String {
 /// 1. Build a template `BTreeMap` with `Value::Undefined` placeholders.
 /// 2. Sort keys by their literal value (BTreeMap order).
 /// 3. Emit `ObjectCreate`.
-#[allow(clippy::indexing_slicing)]
 pub(super) fn build_object_from_keys(
     compiler: &mut Compiler,
     mut keys: Vec<(u16, u8)>,
@@ -812,17 +816,33 @@ pub(super) fn build_object_from_keys(
     // Build template: object with all keys set to Undefined.
     let mut template = BTreeMap::new();
     for &(key_idx, _) in &keys {
-        // SAFETY: key_idx was just returned by `add_literal_u16`, so the
+        // key_idx was returned by `add_literal_u16` in the calling code,
-        // index is guaranteed to be in bounds.
+        // so it is always in bounds.  We use `.get()` + `?` instead of
-        let key_val = compiler.program.literals[usize::from(key_idx)].clone();
+        // direct indexing to satisfy the crate-wide `deny(indexing_slicing)`.
+        let key_val = compiler
+            .program
+            .literals
+            .get(usize::from(key_idx))
+            .ok_or_else(|| {
+                anyhow!(
+                    "internal error in build_object_from_keys: \
+                     literal index {} out of bounds (literals len = {})",
+                    key_idx,
+                    compiler.program.literals.len()
+                )
+            })?
+            .clone();
         template.insert(key_val, Value::Undefined);
     }
     let template_idx = compiler.add_literal_u16(Value::Object(crate::Rc::new(template)))?;
 
-    // Sort keys by literal value (BTreeMap order).
+    // Sort keys by literal value (BTreeMap order).  All indices were
+    // validated in the loop above (which returns Err for out-of-bounds),
+    // so `.get()` always returns `Some` here — `None` is unreachable.
     keys.sort_by(|a, b| {
-        compiler.program.literals[usize::from(a.0)]
+        let a_val = compiler.program.literals.get(usize::from(a.0));
-            .cmp(&compiler.program.literals[usize::from(b.0)])
+        let b_val = compiler.program.literals.get(usize::from(b.0));
+        a_val.cmp(&b_val)
     });
 
     let dest = compiler.alloc_register()?;

src/languages/azure_policy/compiler/mod.rs

@@ -30,11 +30,11 @@ mod metadata;
 mod template_dispatch;
 mod utils;
 
-use alloc::collections::BTreeMap;
+use alloc::string::ToString as _;
-use alloc::string::{String, ToString as _};
 
 use anyhow::Result;
 
+use crate::languages::azure_policy::aliases::AliasRegistry;
 use crate::languages::azure_policy::ast::{PolicyDefinition, PolicyRule};
 use crate::rvm::program::Program;
 use crate::{Rc, Value};
@@ -69,17 +69,14 @@ pub fn compile_policy_rule(rule: &PolicyRule) -> Result<Rc<Program>> {
 
 /// Compile a parsed Azure Policy rule with alias resolution.
 ///
-/// The `alias_map` maps lowercase fully-qualified alias names to their short
+/// The registry provides alias-to-short-name resolution and modifiability
-/// names.  Obtain it from
+/// data.  Pass it as an `Rc` to avoid cloning the internal alias maps.
-/// [`AliasRegistry::alias_map()`](crate::languages::azure_policy::aliases::AliasRegistry::alias_map).
 pub fn compile_policy_rule_with_aliases(
     rule: &PolicyRule,
-    alias_map: BTreeMap<String, String>,
+    registry: Rc<AliasRegistry>,
-    alias_modifiable: BTreeMap<String, bool>,
 ) -> Result<Rc<Program>> {
     let mut compiler = Compiler::new();
-    compiler.alias_map = alias_map;
+    compiler.alias_registry = Some(registry);
-    compiler.alias_modifiable = alias_modifiable;
     init_effect_annotation(&mut compiler, rule);
     compiler.compile(rule)
 }
@@ -100,12 +97,10 @@ pub fn compile_policy_definition(defn: &PolicyDefinition) -> Result<Rc<Program>>
 /// Compile a parsed Azure Policy definition with alias resolution.
 pub fn compile_policy_definition_with_aliases(
     defn: &PolicyDefinition,
-    alias_map: BTreeMap<String, String>,
+    registry: Rc<AliasRegistry>,
-    alias_modifiable: BTreeMap<String, bool>,
 ) -> Result<Rc<Program>> {
     let mut compiler = Compiler::new();
-    compiler.alias_map = alias_map;
+    compiler.alias_registry = Some(registry);
-    compiler.alias_modifiable = alias_modifiable;
     compiler.parameter_defaults = Some(build_parameter_defaults(&defn.parameters)?);
     compiler.populate_definition_metadata(defn);
     init_effect_annotation(&mut compiler, &defn.policy_rule);
@@ -119,13 +114,11 @@ pub fn compile_policy_definition_with_aliases(
 /// a known alias are silently treated as raw property paths.
 pub fn compile_policy_definition_with_aliases_opts(
     defn: &PolicyDefinition,
-    alias_map: BTreeMap<String, String>,
+    registry: Rc<AliasRegistry>,
-    alias_modifiable: BTreeMap<String, bool>,
     alias_fallback_to_raw: bool,
 ) -> Result<Rc<Program>> {
     let mut compiler = Compiler::new();
-    compiler.alias_map = alias_map;
+    compiler.alias_registry = Some(registry);
-    compiler.alias_modifiable = alias_modifiable;
     compiler.alias_fallback_to_raw = alias_fallback_to_raw;
     compiler.parameter_defaults = Some(build_parameter_defaults(&defn.parameters)?);
     compiler.populate_definition_metadata(defn);

tests/azure_policy/mod.rs

@@ -23,8 +23,7 @@ use regorus::languages::azure_policy::aliases::AliasRegistry;
 use regorus::languages::azure_policy::compiler;
 use regorus::languages::azure_policy::parser;
 use regorus::rvm::RegoVM;
-use regorus::Source;
+use regorus::{Rc, Source, Value};
-use regorus::Value;
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 use std::fs;
@@ -194,7 +193,7 @@ fn yaml_test_impl(file: &str) -> Result<()> {
     let test: YamlTest = serde_yaml::from_str(&yaml_str)?;
 
     // Load alias registry if an aliases file is specified.
-    let alias_registry = if let Some(ref aliases_file) = test.aliases {
+    let alias_registry: Option<Rc<AliasRegistry>> = if let Some(ref aliases_file) = test.aliases {
         let aliases_dir = Path::new(file)
             .parent()
             .unwrap_or_else(|| Path::new("."))
@@ -209,7 +208,7 @@ fn yaml_test_impl(file: &str) -> Result<()> {
         })?;
         let mut registry = AliasRegistry::new();
         registry.load_from_json(&aliases_json)?;
-        Some(registry)
+        Some(Rc::new(registry))
     } else {
         None
     };
@@ -281,11 +280,7 @@ fn yaml_test_impl(file: &str) -> Result<()> {
                         );
                     }
                     if let Some(ref registry) = alias_registry {
-                        compiler::compile_policy_definition_with_aliases(
+                        compiler::compile_policy_definition_with_aliases(&defn, Rc::clone(registry))
-                            &defn,
-                            registry.alias_map(),
-                            registry.alias_modifiable_map(),
-                        )
                     } else {
                         compiler::compile_policy_definition(&defn)
                     }
@@ -308,11 +303,7 @@ fn yaml_test_impl(file: &str) -> Result<()> {
                         );
                     }
                     if let Some(ref registry) = alias_registry {
-                        compiler::compile_policy_rule_with_aliases(
+                        compiler::compile_policy_rule_with_aliases(&ast, Rc::clone(registry))
-                            &ast,
-                            registry.alias_map(),
-                            registry.alias_modifiable_map(),
-                        )
                     } else {
                         compiler::compile_policy_rule(&ast)
                     }
@@ -366,7 +357,7 @@ fn yaml_test_impl(file: &str) -> Result<()> {
 
         let mut vm = RegoVM::new();
         vm.load_program(program);
-        vm.set_input(make_input(case, alias_registry.as_ref())?);
+        vm.set_input(make_input(case, alias_registry.as_deref())?);
         vm.set_context(make_context(case)?);
 
         // Load host-await responses (for auditIfNotExists / deployIfNotExists policies).
@@ -391,7 +382,11 @@ fn yaml_test_impl(file: &str) -> Result<()> {
                         if let Some(rt) = effective_type {
                             inject_type_field(&mut raw, rt);
                         }
-                        normalizer::normalize(&raw, Some(registry), case.api_version.as_deref())
+                        normalizer::normalize(
+                            &raw,
+                            Some(registry.as_ref()),
+                            case.api_version.as_deref(),
+                        )
                     } else {
                         raw
                     }