fix compile time array concatenation for slices

closes #866

2 files changed, 29 insertions, 1 deletions

diff --git a/src/ir.cpp b/src/ir.cpp
index ea001adb93..18fd02c297 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -11058,6 +11058,24 @@ static TypeTableEntry *ir_analyze_array_cat(IrAnalyze *ira, IrInstructionBinOp *
         result_type = get_array_type(ira->codegen, child_type, new_len);
 
         out_array_val = out_val;
+    } else if (is_slice(op1_type) || is_slice(op2_type)) {
+        TypeTableEntry *ptr_type = get_pointer_to_type(ira->codegen, child_type, true);
+        result_type = get_slice_type(ira->codegen, ptr_type);
+        out_array_val = create_const_vals(1);
+        out_array_val->special = ConstValSpecialStatic;
+        out_array_val->type = get_array_type(ira->codegen, child_type, new_len);
+
+        out_val->data.x_struct.fields = create_const_vals(2);
+
+        out_val->data.x_struct.fields[slice_ptr_index].type = ptr_type;
+        out_val->data.x_struct.fields[slice_ptr_index].special = ConstValSpecialStatic;
+        out_val->data.x_struct.fields[slice_ptr_index].data.x_ptr.special = ConstPtrSpecialBaseArray;
+        out_val->data.x_struct.fields[slice_ptr_index].data.x_ptr.data.base_array.array_val = out_array_val;
+        out_val->data.x_struct.fields[slice_ptr_index].data.x_ptr.data.base_array.elem_index = 0;
+
+        out_val->data.x_struct.fields[slice_len_index].type = ira->codegen->builtin_types.entry_usize;
+        out_val->data.x_struct.fields[slice_len_index].special = ConstValSpecialStatic;
+        bigint_init_unsigned(&out_val->data.x_struct.fields[slice_len_index].data.x_bigint, new_len);
     } else {
         new_len += 1; // null byte
 
diff --git a/test/cases/eval.zig b/test/cases/eval.zig
index a5b41275bb..d6f7afe864 100644
--- a/test/cases/eval.zig
+++ b/test/cases/eval.zig
@@ -1,4 +1,5 @@
-const assert = @import("std").debug.assert;
+const std = @import("std");
+const assert = std.debug.assert;
 const builtin = @import("builtin");
 
 test "compile time recursion" {
@@ -503,3 +504,12 @@ test "const ptr to comptime mutable data is not memoized" {
         assert(foo.read_x() == 2);
     }
 }
+
+test "array concat of slices gives slice" {
+    comptime {
+        var a: []const u8 = "aoeu";
+        var b: []const u8 = "asdf";
+        const c = a ++ b;
+        assert(std.mem.eql(u8, c, "aoeuasdf"));
+    }
+}