Fix: false positive with print and unused-return-value (#486)

Fixes #474

Signed-off-by: Anders Eknert <anders@styra.com>

bundle/regal/rules/bugs/unused_return_value.rego

@@ -17,6 +17,9 @@ report contains violation if {
 	ref_name := expr.terms[0].value[0].value
 	ref_name in ast.builtin_names
 
+	# special case as the "result" of print is ""
+	ref_name != "print"
+
 	config.capabilities.builtins[ref_name].decl.result != "boolean"
 
 	# no violation if the return value is declared as the last function argument

bundle/regal/rules/bugs/unused_return_value_test.rego

@@ -44,3 +44,11 @@ test_success_function_arg_return_ignored if {
 	}`)
 	r == set()
 }
+
+test_success_not_triggered_by_print if {
+	r := rule.report with data.internal.combined_config as {"capabilities": capabilities.provided}
+		with input as ast.with_rego_v1(`allow if {
+		print(lower("A"))
+	}`)
+	r == set()
+}