From 15662bd32faab90c7b66b17bcf33078d08af5ce3 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Fri, 12 Dec 2025 20:57:32 +0100
Subject: [PATCH] Typedefs and structs with inline types supporting lengthof
 would not work with lengthof #2641.

---
 releasenotes.md               |  1 +
 src/compiler/sema_expr.c      | 19 ++++++++++++++++++-
 test/unit/regression/lenof.c3 | 13 +++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/releasenotes.md b/releasenotes.md
index ecc984f38..58a251c78 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -16,6 +16,7 @@
 - Subscripting of constant slices would sometimes be considered non-constant #2635.
 - Compiler crash when concatenating structs and arrays to an untyped list.
 - Strings assigned to longer arrays would crash codegen, e.g. `char[10] x = "abcd`.
+- Typedefs and structs with inline types supporting lengthof would not work with lengthof #2641.
 
 ### Stdlib changes
 - Add `ThreadPool` join function to wait for all threads to finish in the pool without destroying the threads.
diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index ea625c115..6315fd38f 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -3855,7 +3855,7 @@ RETRY:;
 			{
 				if (len == 0)
 				{
-				if (missing_ref) return *missing_ref = true, false;
+					if (missing_ref) return *missing_ref = true, false;
 					RETURN_SEMA_ERROR(index_expr, "Cannot index into a zero size list.");
 				}
 				if (missing_ref) return *missing_ref = true, false;
@@ -10888,8 +10888,16 @@ static bool sema_expr_analyse_lenof(SemaContext *context, Expr *expr, bool *miss
 	{
 		return sema_insert_method_call(context, expr, len, inner, NULL, false);
 	}
+RETRY:
 	switch (canonical->type_kind)
 	{
+		case TYPE_UNTYPED_LIST:
+			ASSERT_SPAN(expr, expr_is_const_untyped_list(expr));
+			expr_rewrite_const_int(expr, type_isz, vec_size(expr->const_expr.untyped_list));
+			return true;
+		case TYPE_TYPEDEF:
+			canonical = canonical->decl->distinct->type;
+			goto RETRY;
 		case TYPE_ARRAY:
 		case VECTORS:
 			expr_rewrite_const_int(expr, type_isz, canonical->array.len);
@@ -10897,6 +10905,15 @@ static bool sema_expr_analyse_lenof(SemaContext *context, Expr *expr, bool *miss
 		case TYPE_SLICE:
 			expr_rewrite_slice_len(expr, inner, type_isz);
 			return true;
+		case TYPE_STRUCT:
+			if (canonical->decl->is_substruct)
+			{
+				Expr *expr_access = expr_access_inline_member(copy_expr_single(expr), canonical->decl);
+				*expr = *expr_access;
+				canonical = expr->type->canonical;
+				goto RETRY;
+			}
+			FALLTHROUGH;
 		default:
 			if (missing_ref)
 			{
diff --git a/test/unit/regression/lenof.c3 b/test/unit/regression/lenof.c3
index 0cae821c6..bf622feca 100644
--- a/test/unit/regression/lenof.c3
+++ b/test/unit/regression/lenof.c3
@@ -1,6 +1,19 @@
 module regression;
 import std;
 
+struct Foo
+{
+	inline int[2] a;
+}
+
+fn void lengthof_aggregates() @test
+{
+	Foo g;
+	g.len;
+	String foo = "abc";
+	test::eq(lengthof(g), 2);
+	test::eq(lengthof(foo), 3);
+}
 
 fn void lenof_test() @test
 {