[core] typecheck/type_inferencer: Differentiate global symbols

Required for analyzing use of global symbols before global declaration.

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;
@@ -368,7 +368,7 @@ 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 {}",
                                 stmt.location,
@@ -385,8 +385,12 @@ 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 {