Fix ICEs with recursive type declarations

3 files changed, 34 insertions, 16 deletions

diff --git a/include/elna/boot/name_analysis.h b/include/elna/boot/name_analysis.h
index cd3c4f7..8e945b2 100644
--- a/include/elna/boot/name_analysis.h
+++ b/include/elna/boot/name_analysis.h
@@ -27,6 +27,7 @@ along with GCC; see the file COPYING3.  If not see
 #include <memory>
 #include <optional>
 #include <variant>
+#include <vector>
 
 namespace elna::boot
 {
@@ -66,6 +67,19 @@ namespace elna::boot
     };
 
     /**
+     * Cyclic type declaration.
+     */
+    class cyclic_declaration_error final : public diagnostic
+    {
+        std::vector<std::string> cycle;
+
+    public:
+        cyclic_declaration_error(const source_position position, const std::vector<std::string>& cycle);
+
+        std::string what() const override;
+    };
+
+    /**
      * \c const qualifier used incorrectly — wrong position or duplicate.
      */
     class const_qualifier_error final : public diagnostic
@@ -222,6 +236,24 @@ namespace elna::boot
     {
         using resolving_visitor::visit;
 
+        // Traversal state of the recursive type walk: 
+        struct walk_state
+        {
+            // Whether the path passed through a record.
+            bool record_seen{ false };
+            // Whether the current occurrence is behind a pointer or a slice.
+            bool guarded{ false };
+        };
+
+        // Returns the cycle path if wiring the referent closes an illegal
+        // cycle, nothing otherwise.
+        static std::optional<std::vector<std::string>> find_alias_cycle(
+                const std::shared_ptr<alias_type>& being_resolved, const type& referent);
+
+        // Returns whether the referent is well-founded.
+        static bool find_alias_cycle(const std::shared_ptr<alias_type>& being_resolved,
+                const type& referent, std::vector<std::string>& alias_path, walk_state state);
+
     public:
         declaration_visitor(symbol_bag& bag, const target_info& target,
                 const std::filesystem::path& module_path);
diff --git a/include/elna/boot/type_check.h b/include/elna/boot/type_check.h
index 0b62a4a..330de44 100644
--- a/include/elna/boot/type_check.h
+++ b/include/elna/boot/type_check.h
@@ -107,19 +107,6 @@ namespace elna::boot
     };
 
     /**
-     * Cyclic type declaration.
-     */
-    class cyclic_declaration_error final : public diagnostic
-    {
-        std::vector<std::string> cycle;
-
-    public:
-        cyclic_declaration_error(const source_position position, const std::vector<std::string>& cycle);
-
-        std::string what() const override;
-    };
-
-    /**
      * Argument count in a procedure call or array constructor doesn't match
      * the expected number of parameters or elements.
      */
@@ -222,8 +209,6 @@ namespace elna::boot
          */
         static bool is_assignable_from(const type& assignee, const type& assignment);
         static bool is_equality_compatible(const type& left, const type& right);
-        static bool check_unresolved_symbol(const std::shared_ptr<alias_type>& alias,
-                std::vector<std::string>& path);
 
         void visit_and_validate_condition(expression& condition);
 
diff --git a/include/elna/gcc/elna-builtins.h b/include/elna/gcc/elna-builtins.h
index 9f24b00..75b409d 100644
--- a/include/elna/gcc/elna-builtins.h
+++ b/include/elna/gcc/elna-builtins.h
@@ -37,7 +37,8 @@ namespace elna::gcc
     tree handle_symbol(const std::string& symbol_name,
             const std::shared_ptr<boot::alias_type>& reference,
             const std::shared_ptr<symbol_table>& symbols);
-    tree get_inner_alias(const boot::type& type, const std::shared_ptr<symbol_table>& symbols);
+    tree get_inner_alias(const boot::type& type, const std::shared_ptr<symbol_table>& symbols,
+            tree placeholder = NULL_TREE);
     void declare_procedure(const std::string& name, const boot::procedure_info& info,
             const std::shared_ptr<symbol_table>& symbols);
     tree declare_variable(const std::string& name, const boot::variable_info& info,