From b3a7a5731285625aa9fc6a347841591757860edb Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Tue, 1 Sep 2026 01:55:44 +0200
Subject: Fix const extern variable declarations

---
 boot/name_analysis.cc |  2 +-
 boot/type_check.cc    | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

(limited to 'boot')

diff --git a/boot/name_analysis.cc b/boot/name_analysis.cc
index 70b9031..3c4c6f8 100644
--- a/boot/name_analysis.cc
+++ b/boot/name_analysis.cc
@@ -420,7 +420,7 @@ namespace elna::boot
                         non_constant_expression_error::initializer{ extract_identifiers(declaration->identifiers) });
             }
         }
-        else if (resolve_aliases(variable_type).get<constant_type>() != nullptr)
+        else if (!declaration->is_extern && resolve_aliases(variable_type).get<constant_type>() != nullptr)
         {
                 auto position_span = source_position(declaration->identifiers.front().id().position().start(),
                         declaration->identifiers.back().id().position().end());
diff --git a/boot/type_check.cc b/boot/type_check.cc
index 068d958..74c8176 100644
--- a/boot/type_check.cc
+++ b/boot/type_check.cc
@@ -513,12 +513,40 @@ namespace elna::boot
         return verdict::pass;
     }
 
+    assign_check::verdict assign_check::check_array_conversion() const
+    {
+        auto assignee_array = ctx.resolved_assignee.get<array_type>();
+        auto assignment_array = ctx.resolved_assignment.get<array_type>();
+
+        if (assignee_array == nullptr || assignment_array == nullptr
+                || assignee_array->size != assignment_array->size)
+        {
+            return verdict::pass;
+        }
+        auto assignee_element_const = resolve_aliases(assignee_array->base).get<constant_type>();
+        auto assignment_element_const = resolve_aliases(assignment_array->base).get<constant_type>();
+
+        // An array is copied by value, so const can be added to the element type,
+        // but not removed. Writing to such an array is rejected on the lvalue.
+        if (assignee_element_const != nullptr
+                && assignee_element_const->unqualified == assignment_array->base)
+        {
+            return verdict::accept;
+        }
+        if (assignment_element_const != nullptr && assignee_element_const == nullptr)
+        {
+            return verdict::reject;
+        }
+        return verdict::pass;
+    }
+
     bool assign_check::run()
     {
         auto const assign_handlers = {
             &assign_check::guard_const_laundering,
             &assign_check::check_exact_match,
             &assign_check::check_slice_conversion,
+            &assign_check::check_array_conversion,
             &assign_check::check_pointer_hatch,
             &assign_check::check_pointer_conversion
         };
-- 
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