Added explicit migration method signature validation

driver/gomethods/gomethods_migrator.go

@@ -17,7 +17,7 @@ func (e MissingMethodError) Error() string { return "Non existing migrate method
 type WrongMethodSignatureError string
 
 func (e WrongMethodSignatureError) Error() string {
-	return fmt.Sprintf("Method %s has wrong signature", e)
+	return fmt.Sprintf("Method %s has wrong signature", string(e))
 }
 
 type MethodInvocationFailedError struct {
@@ -30,7 +30,7 @@ func (e *MethodInvocationFailedError) Error() string {
 }
 
 type MigrationMethodInvoker interface {
-	IsValid(methodName string) bool
+	Validate(methodName string) error
 	Invoke(methodName string) error
 }
 
@@ -66,8 +66,10 @@ func (m *Migrator) Migrate(f file.File, pipe chan interface{}) error {
 			// on failure, try to rollback methods in this migration
 			for j := i - 1; j >= 0; j-- {
 				rollbackToMethodName := getRollbackToMethod(methods[j])
-				if rollbackToMethodName == "" ||
-					!m.MethodInvoker.IsValid(rollbackToMethodName) {
+				if rollbackToMethodName == "" {
+					continue
+				}
+				if err := m.MethodInvoker.Validate(rollbackToMethodName); err != nil {
 					continue
 				}
 
@@ -140,8 +142,8 @@ func (m *Migrator) getMigrationMethods(f file.File) (methods []string, err error
 		}
 
 		methodName := line
-		if !m.MethodInvoker.IsValid(methodName) {
-			return nil, MissingMethodError(methodName)
+		if err := m.MethodInvoker.Validate(methodName); err != nil {
+			return nil, err
 		}
 
 		methods = append(methods, methodName)

driver/gomethods/gomethods_migrator_test.go

@@ -14,12 +14,12 @@ type FakeGoMethodsInvoker struct {
 	InvokedMethods []string
 }
 
-func (invoker *FakeGoMethodsInvoker) IsValid(methodName string) bool {
+func (invoker *FakeGoMethodsInvoker) Validate(methodName string) error {
 	if methodName == "V001_some_non_existing_method_up" {
-		return false
+		return MissingMethodError(methodName)
 	}
 
-	return true
+	return nil
 }
 
 func (invoker *FakeGoMethodsInvoker) Invoke(methodName string) error {
@@ -30,9 +30,8 @@ func (invoker *FakeGoMethodsInvoker) Invoke(methodName string) error {
 			MethodName: methodName,
 			Err:        SomeError{},
 		}
-	} else {
-		return nil
 	}
+	return nil
 }
 
 type SomeError struct{}

driver/gomethods/mongodb/mongodb.go

@@ -141,8 +141,19 @@ func (driver *MongoDbGoMethodsDriver) Migrate(f file.File, pipe chan interface{}
 	}
 }
 
-func (driver *MongoDbGoMethodsDriver) IsValid(methodName string) bool {
-	return reflect.ValueOf(driver.methodsReceiver).MethodByName(methodName).IsValid()
+func (driver *MongoDbGoMethodsDriver) Validate(methodName string) error {
+	method := reflect.ValueOf(driver.methodsReceiver).MethodByName(methodName)
+	if !method.IsValid() {
+		return gomethods.MissingMethodError(methodName)
+	}
+
+	methodTemplate := func(*mgo.Session) error { return nil }
+
+	if method.Type() != reflect.TypeOf(methodTemplate) {
+		return gomethods.WrongMethodSignatureError(methodName)
+	}
+
+	return nil
 }
 
 func (driver *MongoDbGoMethodsDriver) Invoke(methodName string) error {

driver/gomethods/mongodb_example/methods_receiver.go

@@ -137,3 +137,12 @@ func (r *MyMgoMethodsReceiver) V002_change_user_cleo_to_cleopatra_down(session *
 
 	return c.Update(colQuerier, change)
 }
+
+// Wrong signature methods for testing
+func (r *MyMgoMethodsReceiver) V001_method_with_wrong_signature_up(s string) error {
+	return nil
+}
+
+func (r *MyMgoMethodsReceiver) V001_method_with_wrong_signature_down(session *mgo.Session) (bool, error) {
+	return true, nil
+}

driver/gomethods/mongodb_example/mongodb_test.go

@@ -215,7 +215,7 @@ func TestMigrate(t *testing.T) {
 			},
 		},
 		{
-			name: "v0 -> v1: with error",
+			name: "v0 -> v1: missing method aborts migration",
 			file: file.File{
 				Path:      "/foobar",
 				FileName:  "001_foobar.up.gm",
@@ -235,6 +235,48 @@ func TestMigrate(t *testing.T) {
 				Errors:           []error{gomethods.MissingMethodError("v001_non_existing_method_up")},
 			},
 		},
+		{
+			name: "v0 -> v1: wrong signature method aborts migration",
+			file: file.File{
+				Path:      "/foobar",
+				FileName:  "001_foobar.up.gm",
+				Version:   1,
+				Name:      "foobar",
+				Direction: direction.Up,
+				Content: []byte(`
+						V001_init_organizations_up
+						V001_method_with_wrong_signature_up
+						V001_init_users_up
+					`),
+			},
+			expectedResult: ExpectedMigrationResult{
+				Organizations:    []Organization{},
+				Organizations_v2: []Organization_v2{},
+				Users:            []User{},
+				Errors:           []error{gomethods.WrongMethodSignatureError("V001_method_with_wrong_signature_up")},
+			},
+		},
+		{
+			name: "v1 -> v0: wrong signature method aborts migration",
+			file: file.File{
+				Path:      "/foobar",
+				FileName:  "001_foobar.down.gm",
+				Version:   1,
+				Name:      "foobar",
+				Direction: direction.Down,
+				Content: []byte(`
+						V001_init_users_down
+						V001_method_with_wrong_signature_down
+						V001_init_organizations_down
+					`),
+			},
+			expectedResult: ExpectedMigrationResult{
+				Organizations:    []Organization{},
+				Organizations_v2: []Organization_v2{},
+				Users:            []User{},
+				Errors:           []error{gomethods.WrongMethodSignatureError("V001_method_with_wrong_signature_down")},
+			},
+		},
 	}
 
 	for _, m := range migrations {