From 7494c89a4e1baa08a2720817b06676b34eebb284 Mon Sep 17 00:00:00 2001
From: Bruce Hill <bruce@bruce-hill.com>
Date: Wed, 1 Oct 2025 14:01:51 -0400
Subject: Fixes for indexing into lists with optional item types

---
 src/compile/indexing.c | 16 ++++++++++++++--
 src/typecheck.c        |  6 ++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/compile/indexing.c b/src/compile/indexing.c
index af5056d7..13062641 100644
--- a/src/compile/indexing.c
+++ b/src/compile/indexing.c
@@ -43,8 +43,20 @@ Text_t compile_indexing(env_t *env, ast_t *ast, bool checked) {
                                               : Texts("(Int64_t)(", compile(env, indexing->index), ")"));
         if (checked) {
             int64_t start = (int64_t)(ast->start - ast->file->text), end = (int64_t)(ast->end - ast->file->text);
-            return Texts("List_get_checked(", list, ", ", index_code, ", ", compile_type(item_type), ", ", start, ", ",
-                         end, ")");
+            Text_t code = Texts("List_get_checked(", list, ", ", index_code, ", ", compile_type(item_type), ", ", start,
+                                ", ", end, ")");
+            if (item_type->tag == OptionalType) {
+                int64_t line = get_line_number(ast->file, ast->start);
+                return Texts("({ ", compile_declaration(item_type, Text("opt")), " = ", code, "; ", "if unlikely (",
+                             check_none(item_type, Text("opt")), ")\n", "#line ", line, "\n", "fail_source(",
+                             quoted_str(ast->file->filename), ", ", start, ", ", end, ", ",
+                             "\"This was expected to be a value, but it's `none`\\n\");\n",
+                             optional_into_nonnone(item_type, Text("opt")), "; })");
+            }
+            return code;
+        } else if (item_type->tag == OptionalType) {
+            return Texts("List_get(", list, ", ", index_code, ", ", compile_type(item_type), ", value, value,",
+                         compile_none(item_type), ")");
         } else {
             return Texts("List_get(", list, ", ", index_code, ", ", compile_type(item_type), ", value, ",
                          promote_to_optional(item_type, Text("value")), ", ", compile_none(item_type), ")");
diff --git a/src/typecheck.c b/src/typecheck.c
index 3c820fa9..eff894be 100644
--- a/src/typecheck.c
+++ b/src/typecheck.c
@@ -934,8 +934,10 @@ type_t *get_type(env_t *env, ast_t *ast) {
         if (value_t->tag == ListType) {
             if (!indexing->index) return indexed_t;
             type_t *index_t = get_type(env, indexing->index);
-            if (index_t->tag == IntType || index_t->tag == BigIntType || index_t->tag == ByteType)
-                return Type(OptionalType, Match(value_t, ListType)->item_type);
+            if (index_t->tag == IntType || index_t->tag == BigIntType || index_t->tag == ByteType) {
+                type_t *item_type = Match(value_t, ListType)->item_type;
+                return item_type->tag == OptionalType ? item_type : Type(OptionalType, item_type);
+            }
             code_err(indexing->index, "I only know how to index lists using integers, not ", type_to_text(index_t));
         } else if (value_t->tag == TableType) {
             DeclareMatch(table_type, value_t, TableType);
-- 
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