[core] typecheck: Disallow redeclaration of var shadowing global

nac3core/src/codegen/expr.rs

@@ -2886,7 +2886,31 @@ pub fn gen_expr<'ctx, G: CodeGenerator>(
             Some((_, Some(static_value), _)) => ValueEnum::Static(static_value.clone()),
             None => {
                 let resolver = ctx.resolver.clone();
-                resolver.get_symbol_value(*id, ctx, generator).unwrap()
+                let value = resolver.get_symbol_value(*id, ctx, generator).unwrap();
+
+                let globals = ctx
+                    .top_level
+                    .definitions
+                    .read()
+                    .iter()
+                    .filter_map(|def| {
+                        if let TopLevelDef::Variable { simple_name, ty, .. } = &*def.read() {
+                            Some((*simple_name, *ty))
+                        } else {
+                            None
+                        }
+                    })
+                    .collect_vec();
+
+                if let Some((_, ty)) = globals.iter().find(|(name, _)| name == id) {
+                    let ptr = value
+                        .to_basic_value_enum(ctx, generator, *ty)
+                        .map(BasicValueEnum::into_pointer_value)?;
+
+                    ctx.builder.build_load(ptr, id.to_string().as_str()).map(Into::into).unwrap()
+                } else {
+                    value
+                }
             }
         },
         ExprKind::List { elts, .. } => {

nac3core/src/typecheck/function_check.rs

@@ -10,7 +10,7 @@ use nac3parser::ast::{
 };
 
 use super::{
-    type_inferencer::{IdentifierInfo, Inferencer},
+    type_inferencer::{DeclarationSource, IdentifierInfo, Inferencer},
     typedef::{Type, TypeEnum},
 };
 use crate::toplevel::helper::PrimDef;
@@ -34,6 +34,20 @@ impl<'a> Inferencer<'a> {
                 Err(HashSet::from([format!("cannot assign to a `none` (at {})", pattern.location)]))
             }
             ExprKind::Name { id, .. } => {
+                // If `id` refers to a declared symbol, reject this assignment if it is used in the
+                // context of an (implicit) global variable
+                if let Some(id_info) = self.defined_identifiers.get(id) {
+                    if matches!(
+                        id_info.source,
+                        DeclarationSource::Global { is_explicit: Some(false) }
+                    ) {
+                        return Err(HashSet::from([format!(
+                            "cannot access local variable '{id}' before it is declared (at {})",
+                            pattern.location
+                        )]));
+                    }
+                }
+
                 if !defined_identifiers.contains_key(id) {
                     defined_identifiers.insert(*id, IdentifierInfo::default());
                 }
@@ -104,7 +118,7 @@ impl<'a> Inferencer<'a> {
                         *id,
                     ) {
                         Ok(_) => {
-                            self.defined_identifiers.insert(*id, IdentifierInfo::default());
+                            defined_identifiers.insert(*id, IdentifierInfo::default());
                         }
                         Err(e) => {
                             return Err(HashSet::from([format!(
@@ -368,9 +382,9 @@ impl<'a> Inferencer<'a> {
             StmtKind::Global { names, .. } => {
                 for id in names {
                     if let Some(id_info) = defined_identifiers.get(id) {
-                        if !id_info.is_global {
+                        if id_info.source == DeclarationSource::Local {
                             return Err(HashSet::from([format!(
-                                "name '{id}' is assigned to before global declaration at {}",
+                                "name '{id}' is used prior to global declaration at {}",
                                 stmt.location,
                             )]));
                         }
@@ -385,8 +399,12 @@ impl<'a> Inferencer<'a> {
                         *id,
                     ) {
                         Ok(_) => {
-                            self.defined_identifiers
-                                .insert(*id, IdentifierInfo { is_global: true });
+                            self.defined_identifiers.insert(
+                                *id,
+                                IdentifierInfo {
+                                    source: DeclarationSource::Global { is_explicit: Some(true) },
+                                },
+                            );
                         }
                         Err(e) => {
                             return Err(HashSet::from([format!(

nac3core/src/typecheck/type_inferencer/mod.rs

@@ -88,11 +88,31 @@ impl PrimitiveStore {
     }
 }
 
+/// The location where an identifier declaration refers to.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum DeclarationSource {
+    /// Local scope.
+    Local,
+
+    /// Global scope.
+    Global {
+        /// Whether the identifier is declared by the use of `global` statement. This field is
+        /// [`None`] if the identifier does not refer to a variable.
+        is_explicit: Option<bool>,
+    },
+}
+
 /// Information regarding a defined identifier.
-#[derive(Clone, Copy, Debug, Default)]
+#[derive(Clone, Copy, Debug)]
 pub struct IdentifierInfo {
     /// Whether this identifier refers to a global variable.
-    pub is_global: bool,
+    pub source: DeclarationSource,
+}
+
+impl Default for IdentifierInfo {
+    fn default() -> Self {
+        IdentifierInfo { source: DeclarationSource::Local }
+    }
 }
 
 impl IdentifierInfo {
@@ -566,15 +586,45 @@ impl<'a> Fold<()> for Inferencer<'a> {
                         unreachable!("must be tobj")
                     }
                 } else {
+                    let top_level_defs = &self.top_level.definitions.read();
+
                     if !self.defined_identifiers.contains_key(id) {
                         match self.function_data.resolver.get_symbol_type(
                             self.unifier,
-                            &self.top_level.definitions.read(),
+                            top_level_defs,
                             self.primitives,
                             *id,
                         ) {
                             Ok(_) => {
-                                self.defined_identifiers.insert(*id, IdentifierInfo::default());
+                                // Determine if the referenced id refers to a global symbol
+                                let is_explicit = top_level_defs
+                                    .iter()
+                                    .map(|def| match *def.read() {
+                                        TopLevelDef::Class { name, .. } => (name, false),
+                                        TopLevelDef::Function { simple_name, .. } => {
+                                            (simple_name, false)
+                                        }
+                                        TopLevelDef::Variable { simple_name, .. } => {
+                                            (simple_name, true)
+                                        }
+                                    })
+                                    .find(|(global, _)| global == id)
+                                    .map(|(_, has_explicit_prop)| has_explicit_prop);
+
+                                self.defined_identifiers.insert(
+                                    *id,
+                                    IdentifierInfo {
+                                        source: match is_explicit {
+                                            Some(true) => DeclarationSource::Global {
+                                                is_explicit: Some(false),
+                                            },
+                                            Some(false) => {
+                                                DeclarationSource::Global { is_explicit: None }
+                                            }
+                                            None => DeclarationSource::Local,
+                                        },
+                                    },
+                                );
                             }
                             Err(e) => {
                                 return report_error(