From 759bc1d9093ed4970f27cbd54bab31eb45126d8d Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Thu, 3 Jul 2025 23:32:02 +0200
Subject: [PATCH] Const slice lengths were not always detected as constant.

---
 releasenotes.md                               |  1 +
 src/compiler/sema_casts.c                     |  2 +-
 src/compiler/sema_const.c                     | 12 +++++++++-
 src/compiler/sema_expr.c                      | 24 ++++++-------------
 test/test_suite/slices/const_slice_len.c3     |  6 +++++
 .../struct/inline_slice_access_2088.c3t       |  3 ---
 6 files changed, 26 insertions(+), 22 deletions(-)
 create mode 100644 test/test_suite/slices/const_slice_len.c3

diff --git a/releasenotes.md b/releasenotes.md
index b7c289025..b9650a0bc 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -21,6 +21,7 @@
 - Non-const macros may not return untyped lists.
 - `$for` ct-state not properly popped.
 - Inline `r / complex` for complex numbers fixed.
+- Const slice lengths were not always detected as constant.
 
 ### Stdlib changes
 
diff --git a/src/compiler/sema_casts.c b/src/compiler/sema_casts.c
index 02302b68b..daf342713 100644
--- a/src/compiler/sema_casts.c
+++ b/src/compiler/sema_casts.c
@@ -2214,7 +2214,7 @@ static void cast_slice_to_bool(Expr *expr, Type *type)
 	}
 	if (expr_is_const_slice(expr))
 	{
-		expr_rewrite_const_bool(expr, type, expr->const_expr.slice_init != NULL);
+		expr_rewrite_const_bool(expr, type, expr->const_expr.slice_init != NULL && expr->const_expr.slice_init->kind != CONST_INIT_ZERO);
 		return;
 	}
 	Expr *inner = expr_copy(expr);
diff --git a/src/compiler/sema_const.c b/src/compiler/sema_const.c
index 3ed085605..d7e0186bf 100644
--- a/src/compiler/sema_const.c
+++ b/src/compiler/sema_const.c
@@ -12,7 +12,17 @@ ArrayIndex sema_len_from_const(Expr *expr)
 	// We also handle the case where we have a cast from a const array.
 	if (!sema_cast_const(expr))
 	{
-		if (type_flatten(expr->type)->type_kind != TYPE_SLICE) return -1;
+		Type *flat = type_flatten(expr->type);
+		switch (flat->type_kind)
+		{
+			case TYPE_ARRAY:
+			case TYPE_VECTOR:
+				return flat->array.len;
+			case TYPE_SLICE:
+				break;
+			default:
+				return -1;
+		}
 		if (expr->expr_kind == EXPR_SLICE)
 		{
 			return range_const_len(&expr->slice_expr.range);
diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index 5874aba56..f06f93a24 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -5889,28 +5889,18 @@ CHECK_DEEPER:
 	// 9. Fix hard coded function `len` on slices and arrays
 	if (kw == kw_len)
 	{
+		ArrayIndex index = sema_len_from_const(current_parent);
+		if (index > -1)
+		{
+			expr_rewrite_const_int(expr, type_isz, index);
+			return true;
+		}
 		if (flat_type->type_kind == TYPE_SLICE)
 		{
-			// Handle literal "foo".len which is now a slice.
-			sema_expr_flatten_const_ident(current_parent);
-			if (expr_is_const_string(current_parent))
-			{
-				expr_rewrite_const_int(expr, type_isz, current_parent->const_expr.bytes.len);
-				return true;
-			}
 			expr_rewrite_slice_len(expr, current_parent, type_usz);
 			return true;
 		}
-		if (flat_type->type_kind == TYPE_ARRAY || flat_type->type_kind == TYPE_VECTOR)
-		{
-			expr_rewrite_const_int(expr, type_isz, flat_type->array.len);
-			return true;
-		}
-		if (flat_type->type_kind == TYPE_UNTYPED_LIST)
-		{
-			expr_rewrite_const_int(expr, type_isz, vec_size(current_parent->const_expr.untyped_list));
-			return true;
-		}
+		assert(flat_type->type_kind != TYPE_ARRAY && flat_type->type_kind != TYPE_VECTOR);
 	}
 	if (flat_type->type_kind == TYPE_TYPEID)
 	{
diff --git a/test/test_suite/slices/const_slice_len.c3 b/test/test_suite/slices/const_slice_len.c3
new file mode 100644
index 000000000..79871a513
--- /dev/null
+++ b/test/test_suite/slices/const_slice_len.c3
@@ -0,0 +1,6 @@
+fn int main()
+{
+	const char[][] SEQUENCE = { { 1 }};
+	var $i = SEQUENCE.len;
+	return 0;
+}
\ No newline at end of file
diff --git a/test/test_suite/struct/inline_slice_access_2088.c3t b/test/test_suite/struct/inline_slice_access_2088.c3t
index e97954ec7..4b1985dad 100644
--- a/test/test_suite/struct/inline_slice_access_2088.c3t
+++ b/test/test_suite/struct/inline_slice_access_2088.c3t
@@ -15,8 +15,5 @@ fn int main()
 /* #expect: test.ll
 
 entry:
-  %literal = alloca %Foo, align 8
-  call void @llvm.memset.p0.i64(ptr align 8 %literal, i8 0, i64 16, i1 false)
-  %ptradd = getelementptr inbounds i8, ptr %literal, i64 8
   ret i32 0
 }