goalc: add offset-of (#4081)

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src="https://github.com/user-attachments/assets/841f1885-d438-4baf-ad92-f5996d2f4788"
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Author: Hat-Kid

goalc/compiler/Compiler.h

@@ -730,6 +730,7 @@ class Compiler {
   Val* compile_size_of(const goos::Object& form, const goos::Object& rest, Env* env);
   ConstPropResult const_prop_size_of(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_psize_of(const goos::Object& form, const goos::Object& rest, Env* env);
+  Val* compile_offset_of(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_current_method_id(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_current_method_type(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_cast_to_method_type(const goos::Object& form, const goos::Object& rest, Env* env);

goalc/compiler/compilation/Atoms.cpp

@@ -221,6 +221,7 @@ const std::unordered_map<std::string, GoalCompilerForm> g_goal_forms = {
     {"none", {.form_function = &Compiler::compile_none}},
     {"size-of", {.form_function = &Compiler::compile_size_of}},
     {"psize-of", {.form_function = &Compiler::compile_psize_of}},
+    {"offset-of", {.form_function = &Compiler::compile_offset_of}},
     {"current-method-id", {.form_function = &Compiler::compile_current_method_id}},
     {"cast-to-method-type", {.form_function = &Compiler::compile_cast_to_method_type}},
 

goalc/compiler/compilation/Type.cpp

@@ -1614,6 +1614,26 @@ Val* Compiler::compile_psize_of(const goos::Object& form, const goos::Object& re
   return compile_integer((get_size_for_size_of(form, rest) + 0xf) & ~0xf, env);
 }
 
+Val* Compiler::compile_offset_of(const goos::Object& form, const goos::Object& rest, Env* env) {
+  auto args = get_va(form, rest);
+  va_check(form, args, {goos::ObjectType::SYMBOL, goos::ObjectType::SYMBOL}, {});
+  auto type_to_look_for = args.unnamed.at(0).as_symbol();
+  if (!m_ts.fully_defined_type_exists(type_to_look_for.name_ptr)) {
+    throw_compiler_error(form, "The type {} could not be found or was not fully defined.",
+                         args.unnamed.at(0).print());
+  }
+  auto type = m_ts.lookup_type(type_to_look_for.name_ptr);
+  auto field_name = args.unnamed.at(1).as_symbol().name_ptr;
+  auto as_struct = dynamic_cast<StructureType*>(type);
+  if (as_struct) {
+    auto info = m_ts.lookup_field_info(type->get_name(), field_name);
+    auto off = as_struct->is_boxed() ? info.field.offset() - 4 : info.field.offset();
+    return compile_integer(off, env);
+  } else {
+    throw_compiler_error(form, "The type {} is not a reference type.", args.unnamed.at(0).print());
+  }
+}
+
 Val* Compiler::compile_current_method_id(const goos::Object& form,
                                          const goos::Object& rest,
                                          Env* env) {