feat(azure-policy): add compiler skeleton with core types and stubs

Add the compiler module structure with:
- core.rs: Compiler struct, CountBinding, new(), compile() pipeline,
  register allocation, span/emit helpers
- mod.rs: module declarations, public entry points
  (compile_policy_rule, compile_policy_definition, etc.)
- utils.rs: pure helper functions (path splitting, JSON conversion)
- Stub files for conditions, expressions, fields, template dispatch,
  count, effects, and metadata — real implementations follow in
  subsequent commits.

Author: anakrish

src/languages/azure_policy/compiler/conditions.rs

@@ -0,0 +1,19 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+#![allow(clippy::pattern_type_mismatch, clippy::unused_self)]
+
+//! Constraint / condition / LHS compilation.
+//!
+//! Stub — real implementation added in a later commit.
+
+use anyhow::{bail, Result};
+
+use crate::languages::azure_policy::ast::Constraint;
+
+use super::core::Compiler;
+
+impl Compiler {
+    pub(super) fn compile_constraint(&mut self, _constraint: &Constraint) -> Result<u8> {
+        bail!("condition compilation not yet implemented")
+    }
+}

src/languages/azure_policy/compiler/conditions_wildcard.rs

@@ -0,0 +1,6 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+//! Implicit allOf for unbound `[*]` wildcard fields.
+//!
+//! Stub — real implementation added in a later commit.

src/languages/azure_policy/compiler/core.rs

@@ -0,0 +1,191 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+#![allow(dead_code)]
+#![allow(
+    clippy::arithmetic_side_effects,
+    clippy::as_conversions,
+    clippy::indexing_slicing,
+    clippy::pattern_type_mismatch
+)]
+
+//! Core `Compiler` struct, main compilation pipeline, and register/emit
+//! infrastructure.
+
+use alloc::collections::{BTreeMap, BTreeSet};
+use alloc::string::{String, ToString as _};
+use alloc::vec::Vec;
+
+use anyhow::{anyhow, bail, Result};
+
+use crate::rvm::program::{Program, SpanInfo};
+use crate::rvm::Instruction;
+use crate::{Rc, Value};
+
+use crate::languages::azure_policy::ast::PolicyRule;
+
+// ---------------------------------------------------------------------------
+// Types
+// ---------------------------------------------------------------------------
+
+#[derive(Debug, Clone)]
+pub(super) struct CountBinding {
+    pub(super) name: Option<String>,
+    pub(super) field_wildcard_prefix: Option<String>,
+    pub(super) current_reg: u8,
+}
+
+#[derive(Debug, Default)]
+pub(super) struct Compiler {
+    pub(super) program: Program,
+    pub(super) register_counter: u8,
+    /// High-water mark of `register_counter`.
+    pub(super) register_high_water: u8,
+    pub(super) source_to_index: BTreeMap<String, usize>,
+    pub(super) builtin_index: BTreeMap<String, u16>,
+    pub(super) count_bindings: Vec<CountBinding>,
+    /// Cached register for `LoadInput` — allocated once on first use.
+    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.
+    pub(super) alias_map: BTreeMap<String, String>,
+    /// Map from lowercase fully-qualified alias name → modifiable flag.
+    pub(super) alias_modifiable: BTreeMap<String, bool>,
+    /// Default values for policy parameters.
+    pub(super) parameter_defaults: Option<Value>,
+    /// When set, field conditions resolve against this register instead of
+    /// `input.resource`.  Used for `existenceCondition`.
+    pub(super) resource_override_reg: Option<u8>,
+
+    // -- Metadata accumulators ---------------------------------------------
+    pub(super) observed_field_kinds: BTreeSet<String>,
+    pub(super) observed_aliases: BTreeSet<String>,
+    pub(super) observed_tag_names: BTreeSet<String>,
+    pub(super) observed_operators: BTreeSet<String>,
+    pub(super) observed_resource_types: BTreeSet<String>,
+    pub(super) observed_uses_count: bool,
+    pub(super) observed_has_dynamic_fields: bool,
+    pub(super) observed_has_wildcard_aliases: bool,
+
+    /// When `true`, unknown aliases are silently treated as raw property paths.
+    pub(super) alias_fallback_to_raw: bool,
+}
+
+// ---------------------------------------------------------------------------
+// Core infrastructure
+// ---------------------------------------------------------------------------
+
+impl Compiler {
+    pub(super) fn new() -> Self {
+        Self {
+            register_counter: 0,
+            ..Self::default()
+        }
+    }
+
+    pub(super) fn compile(mut self, rule: &PolicyRule) -> Result<Rc<Program>> {
+        let cond_reg = self.compile_constraint(&rule.condition)?;
+        self.emit(
+            Instruction::ReturnUndefinedIfNotTrue {
+                condition: cond_reg,
+            },
+            &rule.span,
+        );
+
+        let effect_reg = self.compile_effect(rule)?;
+        self.emit(
+            Instruction::Return { value: effect_reg },
+            &rule.then_block.span,
+        );
+
+        self.program.main_entry_point = 0;
+        self.program.entry_points.insert("main".to_string(), 0);
+        self.program.dispatch_window_size = self.register_high_water.max(2);
+        self.program.max_rule_window_size = 0;
+
+        if !self.program.builtin_info_table.is_empty() {
+            self.program.initialize_resolved_builtins()?;
+        }
+
+        self.program
+            .validate_limits()
+            .map_err(|message| anyhow!(message))?;
+
+        self.populate_compiled_annotations();
+
+        Ok(Rc::new(self.program))
+    }
+
+    // -- register / span / emit helpers ------------------------------------
+
+    /// Restore `register_counter` to `saved` while protecting cached registers.
+    pub(super) fn restore_register_counter(&mut self, saved: u8) {
+        let mut floor = saved;
+        if let Some(r) = self.cached_input_reg {
+            floor = floor.max(r.saturating_add(1));
+        }
+        if let Some(r) = self.cached_context_reg {
+            floor = floor.max(r.saturating_add(1));
+        }
+        self.register_counter = floor;
+    }
+
+    pub(super) fn alloc_register(&mut self) -> Result<u8> {
+        if self.register_counter == u8::MAX {
+            bail!("azure-policy compiler exhausted RVM registers");
+        }
+        let reg = self.register_counter;
+        self.register_counter = self.register_counter.saturating_add(1);
+        if self.register_counter > self.register_high_water {
+            self.register_high_water = self.register_counter;
+        }
+        Ok(reg)
+    }
+
+    pub(super) fn span_info(&mut self, span: &crate::lexer::Span) -> SpanInfo {
+        let path = span.source.get_path().to_string();
+        let source_index = if let Some(index) = self.source_to_index.get(path.as_str()) {
+            *index
+        } else {
+            let index = self
+                .program
+                .add_source(path.clone(), span.source.get_contents().to_string());
+            self.source_to_index.insert(path, index);
+            index
+        };
+
+        SpanInfo::from_lexer_span(span, source_index)
+    }
+
+    pub(super) fn emit(&mut self, instruction: Instruction, span: &crate::lexer::Span) {
+        let span_info = self.span_info(span);
+        self.program.add_instruction(instruction, Some(span_info));
+    }
+
+    /// Return the PC (instruction index) that the *next* emitted instruction
+    /// will occupy.
+    pub(super) fn current_pc(&self) -> Result<u16> {
+        u16::try_from(self.program.instructions.len())
+            .map_err(|_| anyhow!("instruction index overflow"))
+    }
+
+    /// Patch tracked instruction indices, setting their `end_pc` field.
+    pub(super) fn patch_end_pc(&mut self, pcs: &[u16], end_pc: u16) {
+        for &pc in pcs {
+            match &mut self.program.instructions[pc as usize] {
+                Instruction::LogicalBlockStart {
+                    end_pc: ref mut ep, ..
+                }
+                | Instruction::AllOfNext {
+                    end_pc: ref mut ep, ..
+                }
+                | Instruction::AnyOfNext {
+                    end_pc: ref mut ep, ..
+                } => {
+                    *ep = end_pc;
+                }
+                _ => {}
+            }
+        }
+    }
+}

src/languages/azure_policy/compiler/count.rs

@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+#![allow(dead_code, clippy::unused_self, clippy::missing_const_for_fn)]
+
+//! `count` / `count.where` loop compilation.
+//!
+//! Stub — real implementation added in a later commit.
+
+use anyhow::{bail, Result};
+
+use crate::languages::azure_policy::ast::{Condition, CountNode};
+
+use super::core::Compiler;
+
+impl Compiler {
+    pub(super) fn compile_count(&mut self, _count_node: &CountNode) -> Result<u8> {
+        bail!("count compilation not yet implemented")
+    }
+
+    pub(super) fn try_compile_count_as_any(
+        &mut self,
+        _count_node: &CountNode,
+        _condition: &Condition,
+    ) -> Result<Option<u8>> {
+        Ok(None)
+    }
+}

src/languages/azure_policy/compiler/count_any.rs

@@ -0,0 +1,6 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+//! Existence-pattern optimization (count → Any loop).
+//!
+//! Stub — real implementation added in a later commit.

src/languages/azure_policy/compiler/count_bindings.rs

@@ -0,0 +1,34 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+#![allow(dead_code, clippy::unused_self, clippy::missing_const_for_fn)]
+
+//! Count-binding resolution and `current()` references.
+//!
+//! Stub — real implementation added in a later commit.
+
+use anyhow::{bail, Result};
+
+use super::core::{Compiler, CountBinding};
+
+impl Compiler {
+    pub(super) fn resolve_count_binding(&self, _field_path: &str) -> Result<Option<CountBinding>> {
+        Ok(None)
+    }
+
+    pub(super) fn compile_from_binding(
+        &mut self,
+        _binding: CountBinding,
+        _field_path: &str,
+        _span: &crate::lexer::Span,
+    ) -> Result<u8> {
+        bail!("count binding compilation not yet implemented")
+    }
+
+    pub(super) fn compile_current_reference(
+        &mut self,
+        _key: &str,
+        _span: &crate::lexer::Span,
+    ) -> Result<u8> {
+        bail!("current() reference not yet implemented")
+    }
+}

src/languages/azure_policy/compiler/effects.rs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+#![allow(dead_code, clippy::unused_self)]
+
+//! Effect compilation (dispatch + cross-resource).
+//!
+//! Stub — real implementation added in a later commit.
+
+use anyhow::{bail, Result};
+
+use crate::languages::azure_policy::ast::PolicyRule;
+
+use super::core::Compiler;
+
+impl Compiler {
+    pub(super) fn compile_effect(&mut self, _rule: &PolicyRule) -> Result<u8> {
+        bail!("effect compilation not yet implemented")
+    }
+
+    pub(super) fn wrap_effect_result(
+        &mut self,
+        _effect_name_reg: u8,
+        _details_reg: Option<u8>,
+        _span: &crate::lexer::Span,
+    ) -> Result<u8> {
+        bail!("wrap_effect_result not yet implemented")
+    }
+}

src/languages/azure_policy/compiler/effects_modify_append.rs

@@ -0,0 +1,6 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+//! Modify / Append effect detail compilation.
+//!
+//! Stub — real implementation added in a later commit.

src/languages/azure_policy/compiler/expressions.rs

@@ -0,0 +1,48 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+#![allow(dead_code, clippy::unused_self)]
+
+//! Template-expression and call-expression compilation.
+//!
+//! Stub — real implementation added in a later commit.
+
+use anyhow::{bail, Result};
+
+use crate::languages::azure_policy::ast::{Expr, JsonValue, ValueOrExpr};
+
+use super::core::Compiler;
+
+impl Compiler {
+    pub(super) fn compile_value_or_expr(
+        &mut self,
+        _voe: &ValueOrExpr,
+        _span: &crate::lexer::Span,
+    ) -> Result<u8> {
+        bail!("expression compilation not yet implemented")
+    }
+
+    pub(super) fn compile_json_value(
+        &mut self,
+        _value: &JsonValue,
+        _span: &crate::lexer::Span,
+    ) -> Result<u8> {
+        bail!("JSON value compilation not yet implemented")
+    }
+
+    pub(super) fn compile_expr(&mut self, _expr: &Expr) -> Result<u8> {
+        bail!("expression compilation not yet implemented")
+    }
+
+    pub(super) fn compile_call_expr(
+        &mut self,
+        _span: &crate::lexer::Span,
+        _func: &str,
+        _args: &[Expr],
+    ) -> Result<u8> {
+        bail!("call expression compilation not yet implemented")
+    }
+
+    pub(super) fn compile_call_args(&mut self, _args: &[Expr]) -> Result<alloc::vec::Vec<u8>> {
+        bail!("call args compilation not yet implemented")
+    }
+}