Concatenating an const empty slice with another array caused a null p…

…ointer access.

releasenotes.md

@@ -12,6 +12,7 @@
 - Compiler allows a generic module to be declared with different parameters #1856.
 - Fix issue with `@const` where the statement `$foo = 1;` was not considered constant.
 - Const strings and bytes were not properly converted to compile time bools.
+- Concatenating an const empty slice with another array caused a null pointer access.
 
 ### Stdlib changes
 - Added '%h' and '%H' for printing out binary data in hexadecimal using the formatter.

src/compiler/sema_const.c

@@ -417,6 +417,8 @@ bool sema_expr_analyse_ct_concat(SemaContext *context, Expr *concat_expr, Expr *
 				continue;
 			}
 			ConstInitializer *init = expr_const_initializer_from_expr(single_expr);
+			// Skip zero arrays from slices.
+			if (!init) continue;
 			if (init && init->kind != CONST_INIT_ARRAY_FULL)
 			{
 				ASSERT0(!init || init->type != type_untypedlist);

test/test_suite/compile_time/concat_zero_slice.c3t

@@ -0,0 +1,6 @@
+fn int main()
+{
+	char[] $res;
+	$res = { '0' } +++ $res;
+    return 0;
+}