From 9a0010b186a281740af812452514b260b6063e1a Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Tue, 28 Dec 2021 00:03:03 +0200
Subject: [PATCH] stage1: fix access of slice sentinel at comptime

---
 src/stage1/ir.cpp              |  6 +++++-
 test/behavior/slice_stage1.zig | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/stage1/ir.cpp b/src/stage1/ir.cpp
index 3037717614..acde4232a1 100644
--- a/src/stage1/ir.cpp
+++ b/src/stage1/ir.cpp
@@ -14982,12 +14982,16 @@ static Stage1AirInst *ir_analyze_instruction_elem_ptr(IrAnalyze *ira, Stage1ZirI
                         case ConstPtrSpecialSubArray:
                         case ConstPtrSpecialBaseArray:
                             {
+                                uint64_t array_len = ptr_field->data.x_ptr.data.base_array.array_val->type->data.array.len;
+                                if (ptr_field->data.x_ptr.data.base_array.array_val->type->data.array.sentinel != nullptr) {
+                                    array_len += 1;
+                                }
                                 size_t offset = ptr_field->data.x_ptr.data.base_array.elem_index;
                                 uint64_t new_index = offset + index;
                                 if (ptr_field->data.x_ptr.data.base_array.array_val->data.x_array.special !=
                                         ConstArraySpecialBuf)
                                 {
-                                    if (new_index >= ptr_field->data.x_ptr.data.base_array.array_val->type->data.array.len) {
+                                    if (new_index >= array_len) {
                                         ir_add_error_node(ira, elem_ptr_instruction->base.source_node, buf_sprintf("out of bounds slice"));
                                         return ira->codegen->invalid_inst_gen;
                                     }
diff --git a/test/behavior/slice_stage1.zig b/test/behavior/slice_stage1.zig
index 5bbadc3cc6..3df7a75e10 100644
--- a/test/behavior/slice_stage1.zig
+++ b/test/behavior/slice_stage1.zig
@@ -339,3 +339,21 @@ test "slice bounds in comptime concatenation" {
     try expect(str2.len == 1);
     try expect(std.mem.eql(u8, str2, "1"));
 }
+
+test "slice sentinel access at comptime" {
+    {
+        const str0 = &[_:0]u8{ '1', '2', '3' };
+        const slice0: [:0]const u8 = str0;
+
+        try expect(slice0.len == 3);
+        try expect(slice0[slice0.len] == 0);
+    }
+    {
+        const str0 = "123";
+        _ = &str0[0];
+        const slice0: [:0]const u8 = str0;
+
+        try expect(slice0.len == 3);
+        try expect(slice0[slice0.len] == 0);
+    }
+}