api: Test return types

api/api_test.go

@@ -1,12 +1,16 @@
 package api
 
 import (
+	"encoding/json"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"strings"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func goCmd() string {
@@ -32,3 +36,68 @@ func TestDoesntDependOnFFI(t *testing.T) {
 		}
 	}
 }
+
+func TestReturnTypes(t *testing.T) {
+	errType := reflect.TypeOf(new(error)).Elem()
+	bareIface := reflect.TypeOf(new(interface{})).Elem()
+	jmarsh := reflect.TypeOf(new(json.Marshaler)).Elem()
+
+	tst := func(api interface{}) func(t *testing.T) {
+		return func(t *testing.T) {
+			ra := reflect.TypeOf(api).Elem()
+			for i := 0; i < ra.NumMethod(); i++ {
+				m := ra.Method(i)
+				switch m.Type.NumOut() {
+				case 1: // if 1 return value, it must be an error
+					require.Equal(t, errType, m.Type.Out(0), m.Name)
+
+				case 2: // if 2 return values, first cant be an interface/function, second must be an error
+					seen := map[reflect.Type]struct{}{}
+					todo := []reflect.Type{m.Type.Out(0)}
+					for len(todo) > 0 {
+						typ := todo[len(todo) - 1]
+						todo = todo[:len(todo)-1]
+
+						if _, ok := seen[typ]; ok {
+							continue
+						}
+						seen[typ] = struct{}{}
+
+						if typ.Kind() == reflect.Interface && typ != bareIface && !typ.Implements(jmarsh) {
+							t.Error("methods can't return interfaces", m.Name)
+						}
+
+						switch typ.Kind() {
+						case reflect.Ptr:
+							fallthrough
+						case reflect.Array:
+							fallthrough
+						case reflect.Slice:
+							fallthrough
+						case reflect.Chan:
+							todo = append(todo, typ.Elem())
+						case reflect.Map:
+							todo = append(todo, typ.Elem())
+							todo = append(todo, typ.Key())
+						case reflect.Struct:
+							for i := 0; i < typ.NumField(); i++ {
+								todo = append(todo, typ.Field(i).Type)
+							}
+						}
+					}
+
+					require.NotEqual(t, reflect.Func.String(), m.Type.Out(0).Kind().String(), m.Name)
+					require.Equal(t, errType, m.Type.Out(1), m.Name)
+
+				default:
+					t.Error("methods can only have 1 or 2 return values", m.Name)
+				}
+			}
+		}
+	}
+
+	t.Run("common", tst(new(Common)))
+	t.Run("full", tst(new(FullNode)))
+	t.Run("miner", tst(new(StorageMiner)))
+	t.Run("worker", tst(new(WorkerAPI)))
+}