add package errext

The ErrorSet type comes from Limes. I want to use it in Castellum, too.

README.md

@@ -10,6 +10,7 @@ reusability. Feel free to add to this.
 * [assert](./assert) contains various assertions for unit tests.
 * [audittools](./audittools) contains helper functions for establishing a connection to a RabbitMQ server (with sane defaults) and publishing messages to it.
 * [easypg](./easypg) is a database library for applications that use PostgreSQL. It integrates [golang-migrate/migrate](https://github.com/golang-migrate/migrate) for data definition and imports the libpq-based SQL driver.
+* [errext](./errext) contains convenience functions for handling and propagating errors.
 * [gopherpolicy](./gopherpolicy) integrates [Gophercloud](https://github.com/gophercloud/gophercloud) with [goslo.policy](https://github.com/databus23/goslo.policy), for OpenStack services that need to validate client tokens and check permissions.
 * [httpapi](./httpapi) contains opinionated base machinery for assembling and exposing an API consisting of HTTP endpoints.
 * [httpext](./httpext) adds some convenience functions to [net/http](https://golang.org/pkg/http/).

errext/errext.go

@@ -0,0 +1,21 @@
+/*******************************************************************************
+*
+* Copyright 2023 SAP SE
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You should have received a copy of the License along with this
+* program. If not, you may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*
+*******************************************************************************/
+
+// Package errext contains convenience functions for handling and propagating errors.
+package errext

errext/errorset.go

@@ -0,0 +1,67 @@
+/*******************************************************************************
+*
+* Copyright 2023 SAP SE
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You should have received a copy of the License along with this
+* program. If not, you may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*
+*******************************************************************************/
+
+package errext
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/sapcc/go-bits/logg"
+)
+
+// ErrorSet replaces the "error" return value in functions that can return
+// multiple errors. It provides convenience functions for easily adding errors
+// to the set.
+type ErrorSet []error
+
+// Add adds the given error to the set if it is non-nil.
+func (errs *ErrorSet) Add(err error) {
+	if err != nil {
+		*errs = append(*errs, err)
+	}
+}
+
+// Addf is a shorthand for errs.Add(fmt.Errorf(...)).
+func (errs *ErrorSet) Addf(msg string, args ...any) {
+	*errs = append(*errs, fmt.Errorf(msg, args...))
+}
+
+// Append adds all errors from the `other` ErrorSet to this one.
+func (errs *ErrorSet) Append(other ErrorSet) {
+	*errs = append(*errs, other...)
+}
+
+// IsEmpty returns true if no errors are in the set.
+func (errs ErrorSet) IsEmpty() bool {
+	return len(errs) == 0
+}
+
+// LogFatalIfError reports all errors in this set on level FATAL, thus dying if
+// there are any errors.
+func (errs ErrorSet) LogFatalIfError() {
+	hasErrors := false
+	for _, err := range errs {
+		hasErrors = true
+		logg.Other("FATAL", err.Error())
+	}
+	if hasErrors {
+		os.Exit(1)
+	}
+}