feat(hoist): pre-compute loop hoisting metadata at compilation time

Introduce a compiler pass that analyzes and pre-computes loop hoisting information
during policy compilation. This hoisted metadata is stored in lookup tables and made
available to downstream consumers:

- interpreter: use HoistedLoop entries during evaluation (replaces runtime scanning)
- type inference: can leverage pre-computed loop structure for type propagation
- RVM compiler: will consume hoisting metadata for optimized bytecode generation

Changes:
- populate loop hoisting tables during engine preparation and query snippet execution
- refactor eval_stmts_in_loop and eval_output_expr_in_loop to consume HoistedLoop directly
- add helper methods for accessing loop expressions, collections, and indices from HoistedLoop
- extend Lookup with get_checked and into_slots for safe query context access and merging

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

Author: anakrish

src/compiled_policy.rs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 use crate::ast::*;
+use crate::compiler::hoist::HoistedLoopsLookup;
 use crate::engine::Engine;
 use crate::scheduler::*;
 use crate::utils::*;
@@ -212,4 +213,7 @@ pub(crate) struct CompiledPolicyData {
 
     // The semantics of extensions ought to be changes to be more Clone friendly.
     pub(crate) extensions: Map<String, (u8, Rc<Box<dyn Extension>>)>,
+
+    // Pre-computed loop hoisting information
+    pub(crate) loop_hoisting_table: HoistedLoopsLookup,
 }

src/compiler.rs

@@ -0,0 +1,10 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+//! Compiler-related functionality for Regorus.
+//!
+//! This module contains utilities and data structures used during
+//! the compilation phase to prepare policies for efficient execution.
+
+pub mod context;
+pub mod hoist;

src/compiler/context.rs

@@ -0,0 +1,153 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+//! Compilation context types shared across compiler components.
+//!
+//! This module defines context structures used for tracking scope-level information
+//! during compilation and analysis phases. These types are designed to be compatible
+//! with both the interpreter's loop hoisting and the RVM compiler.
+
+use crate::ast::ExprRef;
+use alloc::collections::BTreeSet;
+use alloc::string::{String, ToString};
+
+/// Type of compilation context for tracking different scenarios
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ContextType {
+    /// Rule context (Complete, PartialSet, PartialObject, or Function)
+    Rule,
+    /// Comprehension context (Array, Set, or Object)
+    Comprehension,
+    /// Every quantifier context
+    Every,
+    /// Query/statement context (no output expressions)
+    Query,
+}
+
+/// Context for tracking variable bindings and output expressions within a scope.
+/// Used during loop hoisting and compilation to determine what needs to be hoisted
+/// and what's already bound.
+///
+/// This design is compatible with RVM's CompilationContext for potential future unification.
+#[derive(Debug, Clone)]
+pub struct ScopeContext {
+    /// Type of context (Rule, Comprehension, Every, Query)
+    pub context_type: ContextType,
+
+    /// Variables that are bound in the current scope
+    pub bound_vars: BTreeSet<String>,
+
+    /// Variables that are explicitly marked as unbound (from `some` declarations)
+    pub unbound_vars: BTreeSet<String>,
+
+    /// Key expression from rule head or object comprehension (for output expression hoisting)
+    pub key_expr: Option<ExprRef>,
+
+    /// Value expression from rule assignment or comprehension term (for output expression hoisting)
+    pub value_expr: Option<ExprRef>,
+}
+
+impl ScopeContext {
+    /// Create a new context with Query type (default, no output expressions)
+    pub fn new() -> Self {
+        Self {
+            context_type: ContextType::Query,
+            bound_vars: BTreeSet::new(),
+            unbound_vars: BTreeSet::new(),
+            key_expr: None,
+            value_expr: None,
+        }
+    }
+
+    /// Create a new context with a specific context type
+    pub fn with_context_type(context_type: ContextType) -> Self {
+        Self {
+            context_type,
+            bound_vars: BTreeSet::new(),
+            unbound_vars: BTreeSet::new(),
+            key_expr: None,
+            value_expr: None,
+        }
+    }
+
+    /// Create a new context with output expressions (for rules and comprehensions)
+    pub fn with_output_exprs(
+        context_type: ContextType,
+        key_expr: Option<ExprRef>,
+        value_expr: Option<ExprRef>,
+    ) -> Self {
+        Self {
+            context_type,
+            bound_vars: BTreeSet::new(),
+            unbound_vars: BTreeSet::new(),
+            key_expr,
+            value_expr,
+        }
+    }
+
+    /// Create a child context that inherits bindings but overrides context type and output expressions
+    pub fn child_with_output_exprs(
+        &self,
+        context_type: ContextType,
+        key_expr: Option<ExprRef>,
+        value_expr: Option<ExprRef>,
+    ) -> Self {
+        Self {
+            context_type,
+            bound_vars: self.bound_vars.clone(),
+            unbound_vars: self.unbound_vars.clone(),
+            key_expr,
+            value_expr,
+        }
+    }
+
+    /// Add a variable to the bound set
+    pub fn bind_variable(&mut self, var_name: &str) {
+        if var_name != "_" {
+            self.bound_vars.insert(var_name.to_string());
+            self.unbound_vars.remove(var_name);
+        }
+    }
+
+    /// Mark a variable as unbound
+    pub fn add_unbound_variable(&mut self, var_name: &str) {
+        if var_name != "_" && !self.bound_vars.contains(var_name) {
+            self.unbound_vars.insert(var_name.to_string());
+        }
+    }
+
+    /// Check if a variable is known to be unbound
+    pub fn is_unbound(&self, var_name: &str) -> bool {
+        self.unbound_vars.contains(var_name)
+    }
+
+    /// Check if we can determine that a variable should be treated as a loop iterator
+    /// (either it's unbound or explicitly marked as such)
+    pub fn should_hoist_as_loop(&self, var_name: &str) -> bool {
+        if var_name == "_" {
+            true
+        } else if self.is_unbound(var_name) {
+            true
+        } else {
+            // Treat variables that haven't been bound in this scope as potential loop iterators
+            !self.bound_vars.contains(var_name)
+        }
+    }
+
+    /// Create a child context inheriting parent bindings, output expressions, and context type
+    pub fn child(&self) -> Self {
+        Self {
+            context_type: self.context_type.clone(),
+            bound_vars: self.bound_vars.clone(),
+            unbound_vars: self.unbound_vars.clone(),
+            key_expr: self.key_expr.clone(),
+            value_expr: self.value_expr.clone(),
+        }
+    }
+}
+
+impl Default for ScopeContext {
+    fn default() -> Self {
+        Self::new()
+    }
+}