chore(experimental): Add compiler option to enable the Elaborator (#5003

)

# Description

## Problem\*

Working towards #4594 

## Summary\*

Adds a hidden compiler option `--use-elaborator` to enable the
experimental elaborator code to be run on a codebase.

This also connects the elaborator with `dc_crate` (and thus the cli flag
above) by filling in the stub for elaborating functions. Filling in the
stub required quite a bit of code but it was as usual just copied from
name resolution and type checking.

## Additional Context

Originally I wanted to connect the elaborator to more of the frontend
(e.g. resolve globals, types, traits, etc) but this already ballooned to
a large line count. To review I'd recommend reviewing the non-elaborator
portions first then just skimming through the elaborator portions since
they are copied from `Resolver::resolve_function`,
`Resolver::extract_meta`, `Resolver::intern_function`, and
`type_check_func`.

## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [ ] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_driver/src/lib.rs

@@ -103,6 +103,10 @@ pub struct CompileOptions {
     /// Force Brillig output (for step debugging)
     #[arg(long, hide = true)]
     pub force_brillig: bool,
+
+    /// Enable the experimental elaborator pass
+    #[arg(long, hide = true)]
+    pub use_elaborator: bool,
 }
 
 fn parse_expression_width(input: &str) -> Result<ExpressionWidth, std::io::Error> {
@@ -245,12 +249,13 @@ pub fn check_crate(
     crate_id: CrateId,
     deny_warnings: bool,
     disable_macros: bool,
+    use_elaborator: bool,
 ) -> CompilationResult<()> {
     let macros: &[&dyn MacroProcessor] =
         if disable_macros { &[] } else { &[&aztec_macros::AztecMacro as &dyn MacroProcessor] };
 
     let mut errors = vec![];
-    let diagnostics = CrateDefMap::collect_defs(crate_id, context, macros);
+    let diagnostics = CrateDefMap::collect_defs(crate_id, context, use_elaborator, macros);
     errors.extend(diagnostics.into_iter().map(|(error, file_id)| {
         let diagnostic = CustomDiagnostic::from(&error);
         diagnostic.in_file(file_id)
@@ -282,8 +287,13 @@ pub fn compile_main(
     options: &CompileOptions,
     cached_program: Option<CompiledProgram>,
 ) -> CompilationResult<CompiledProgram> {
-    let (_, mut warnings) =
-        check_crate(context, crate_id, options.deny_warnings, options.disable_macros)?;
+    let (_, mut warnings) = check_crate(
+        context,
+        crate_id,
+        options.deny_warnings,
+        options.disable_macros,
+        options.use_elaborator,
+    )?;
 
     let main = context.get_main_function(&crate_id).ok_or_else(|| {
         // TODO(#2155): This error might be a better to exist in Nargo
@@ -318,8 +328,13 @@ pub fn compile_contract(
     crate_id: CrateId,
     options: &CompileOptions,
 ) -> CompilationResult<CompiledContract> {
-    let (_, warnings) =
-        check_crate(context, crate_id, options.deny_warnings, options.disable_macros)?;
+    let (_, warnings) = check_crate(
+        context,
+        crate_id,
+        options.deny_warnings,
+        options.disable_macros,
+        options.use_elaborator,
+    )?;
 
     // TODO: We probably want to error if contracts is empty
     let contracts = context.get_all_contracts(&crate_id);

compiler/noirc_driver/tests/stdlib_warnings.rs

@@ -24,7 +24,8 @@ fn stdlib_does_not_produce_constant_warnings() -> Result<(), ErrorsAndWarnings>
     let mut context = Context::new(file_manager, parsed_files);
     let root_crate_id = prepare_crate(&mut context, file_name);
 
-    let ((), warnings) = noirc_driver::check_crate(&mut context, root_crate_id, false, false)?;
+    let ((), warnings) =
+        noirc_driver::check_crate(&mut context, root_crate_id, false, false, false)?;
 
     assert_eq!(warnings, Vec::new(), "stdlib is producing warnings");
 

compiler/noirc_frontend/src/ast/function.rs

@@ -32,6 +32,15 @@ pub enum FunctionKind {
     Recursive,
 }
 
+impl FunctionKind {
+    pub fn can_ignore_return_type(self) -> bool {
+        match self {
+            FunctionKind::LowLevel | FunctionKind::Builtin | FunctionKind::Oracle => true,
+            FunctionKind::Normal | FunctionKind::Recursive => false,
+        }
+    }
+}
+
 impl NoirFunction {
     pub fn normal(def: FunctionDefinition) -> NoirFunction {
         NoirFunction { kind: FunctionKind::Normal, def }

compiler/noirc_frontend/src/elaborator/expressions.rs

@@ -32,7 +32,7 @@ use crate::{
 
 use super::Elaborator;
 
-impl Elaborator {
+impl<'context> Elaborator<'context> {
     pub(super) fn elaborate_expression(&mut self, expr: Expression) -> (ExprId, Type) {
         let (hir_expr, typ) = match expr.kind {
             ExpressionKind::Literal(literal) => self.elaborate_literal(literal, expr.span),
@@ -323,7 +323,7 @@ impl Elaborator {
                     &method_ref,
                     object_type,
                     location,
-                    &mut self.interner,
+                    self.interner,
                 );
 
                 let func_type = self.type_check_variable(function_name, function_id);
@@ -443,7 +443,7 @@ impl Elaborator {
         (expr_id, typ)
     }
 
-    fn intern_expr(&mut self, expr: HirExpression, span: Span) -> ExprId {
+    pub fn intern_expr(&mut self, expr: HirExpression, span: Span) -> ExprId {
         let id = self.interner.push_expr(expr);
         self.interner.push_expr_location(id, span, self.file);
         id