chore(experimental): Elaborate globals (#5069)

# Description

## Problem\*

Working towards #4992 

## Summary\*

Adds support for elaborating globals. This was the last major item for
resolution + type checking in the elaborator.

## Additional Context

Next up in the elaborator will be integrating the scanning
pass/interpreter and hooking it up to our integration tests.

## 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_frontend/src/elaborator/mod.rs

@@ -11,7 +11,10 @@ use crate::{
     },
     hir::{
         def_collector::{
-            dc_crate::{CompilationError, UnresolvedStruct, UnresolvedTrait, UnresolvedTypeAlias},
+            dc_crate::{
+                filter_literal_globals, CompilationError, UnresolvedGlobal, UnresolvedStruct,
+                UnresolvedTrait, UnresolvedTypeAlias,
+            },
             errors::DuplicateType,
         },
         resolution::{errors::ResolverError, path_resolver::PathResolver, resolver::LambdaContext},
@@ -25,13 +28,14 @@ use crate::{
             HirInfixExpression, HirLambda, HirMemberAccess, HirMethodCallExpression,
             HirMethodReference, HirPrefixExpression,
         },
+        stmt::HirLetStatement,
         traits::TraitConstraint,
     },
     macros_api::{
         BlockExpression, CallExpression, CastExpression, Expression, ExpressionKind, HirExpression,
         HirLiteral, HirStatement, Ident, IndexExpression, Literal, MemberAccessExpression,
-        MethodCallExpression, NodeInterner, NoirFunction, NoirStruct, PrefixExpression, Statement,
-        StatementKind, StructId,
+        MethodCallExpression, NodeInterner, NoirFunction, NoirStruct, Pattern, PrefixExpression,
+        SecondaryAttribute, Statement, StatementKind, StructId,
     },
     node_interner::{DefinitionKind, DependencyId, ExprId, FuncId, StmtId, TraitId, TypeAliasId},
     Shared, StructType, Type, TypeVariable,
@@ -207,25 +211,48 @@ impl<'context> Elaborator<'context> {
     ) -> Vec<(CompilationError, FileId)> {
         let mut this = Self::new(context, crate_id);
 
-        // the resolver filters literal globals first
-        for global in items.globals {}
+        // We must first resolve and intern the globals before we can resolve any stmts inside each function.
+        // Each function uses its own resolver with a newly created ScopeForest, and must be resolved again to be within a function's scope
+        //
+        // Additionally, we must resolve integer globals before structs since structs may refer to
+        // the values of integer globals as numeric generics.
+        let (literal_globals, non_literal_globals) = filter_literal_globals(items.globals);
+
+        for global in literal_globals {
+            this.elaborate_global(global);
+        }
 
         for (alias_id, alias) in items.type_aliases {
             this.define_type_alias(alias_id, alias);
         }
 
         this.collect_traits(items.traits);
+
+        // Must resolve structs before we resolve globals.
         this.collect_struct_definitions(items.types);
 
+        // Bind trait impls to their trait. Collect trait functions, that have a
+        // default implementation, which hasn't been overridden.
         for trait_impl in &mut items.trait_impls {
             this.collect_trait_impl(trait_impl);
         }
 
+        // Before we resolve any function symbols we must go through our impls and
+        // re-collect the methods within into their proper module. This cannot be
+        // done during def collection since we need to be able to resolve the type of
+        // the impl since that determines the module we should collect into.
+        //
+        // These are resolved after trait impls so that struct methods are chosen
+        // over trait methods if there are name conflicts.
         for ((typ, module), impls) in &items.impls {
             this.collect_impls(typ, *module, impls);
         }
 
-        // resolver resolves non-literal globals here
+        // We must wait to resolve non-literal globals until after we resolve structs since struct
+        // globals will need to reference the struct type they're initialized to to ensure they are valid.
+        for global in non_literal_globals {
+            this.elaborate_global(global);
+        }
 
         for functions in items.functions {
             this.elaborate_functions(functions);
@@ -1173,4 +1200,33 @@ impl<'context> Elaborator<'context> {
 
         (generics, fields)
     }
+
+    fn elaborate_global(&mut self, global: UnresolvedGlobal) {
+        self.local_module = global.module_id;
+        self.file = global.file_id;
+
+        let global_id = global.global_id;
+        self.current_item = Some(DependencyId::Global(global_id));
+
+        let definition_kind = DefinitionKind::Global(global_id);
+        let let_stmt = global.stmt_def;
+
+        if !self.in_contract
+            && let_stmt.attributes.iter().any(|attr| matches!(attr, SecondaryAttribute::Abi(_)))
+        {
+            let span = let_stmt.pattern.span();
+            self.push_err(ResolverError::AbiAttributeOutsideContract { span });
+        }
+
+        if !let_stmt.comptime && matches!(let_stmt.pattern, Pattern::Mutable(..)) {
+            let span = let_stmt.pattern.span();
+            self.push_err(ResolverError::MutableGlobal { span });
+        }
+
+        let (let_statement, _typ) = self.elaborate_let(let_stmt);
+
+        let statement_id = self.interner.get_global(global_id).let_statement;
+        self.interner.get_global_definition_mut(global_id).kind = definition_kind;
+        self.interner.replace_statement(statement_id, let_statement);
+    }
 }

compiler/noirc_frontend/src/hir/def_collector/dc_crate.rs

@@ -486,7 +486,7 @@ fn inject_prelude(
 /// Separate the globals Vec into two. The first element in the tuple will be the
 /// literal globals, except for arrays, and the second will be all other globals.
 /// We exclude array literals as they can contain complex types
-fn filter_literal_globals(
+pub fn filter_literal_globals(
     globals: Vec<UnresolvedGlobal>,
 ) -> (Vec<UnresolvedGlobal>, Vec<UnresolvedGlobal>) {
     globals.into_iter().partition(|global| match &global.stmt_def.expression.kind {

compiler/noirc_frontend/src/node_interner.rs

@@ -916,6 +916,13 @@ impl NodeInterner {
         &self.definitions[id.0]
     }
 
+    /// Retrieves the definition where the given id was defined.
+    /// This will panic if given DefinitionId::dummy_id. Use try_definition for
+    /// any call with a possibly undefined variable.
+    pub fn definition_mut(&mut self, id: DefinitionId) -> &mut DefinitionInfo {
+        &mut self.definitions[id.0]
+    }
+
     /// Tries to retrieve the given id's definition.
     /// This function should be used during name resolution or type checking when we cannot be sure
     /// all variables have corresponding definitions (in case of an error in the user's code).
@@ -997,6 +1004,11 @@ impl NodeInterner {
         self.definition(global.definition_id)
     }
 
+    pub fn get_global_definition_mut(&mut self, global_id: GlobalId) -> &mut DefinitionInfo {
+        let global = self.get_global(global_id);
+        self.definition_mut(global.definition_id)
+    }
+
     pub fn get_all_globals(&self) -> &[GlobalInfo] {
         &self.globals
     }