From a9cff5b05e1c46a0ea0ac5d5d652217ccf28d13f Mon Sep 17 00:00:00 2001
From: Stephan Renatus <stephan@styra.com>
Date: Wed, 28 Jun 2023 11:22:02 +0200
Subject: [PATCH] build: add errors.Join workaround for go <1.20

Signed-off-by: Stephan Renatus <stephan@styra.com>
---
 internal/errors/join.go        | 53 ++++++++++++++++++++++++++++++++++
 internal/errors/join_go1.20.go |  7 +++++
 plugins/discovery/discovery.go |  2 +-
 plugins/plugins.go             |  2 +-
 4 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 internal/errors/join.go
 create mode 100644 internal/errors/join_go1.20.go

diff --git a/internal/errors/join.go b/internal/errors/join.go
new file mode 100644
index 0000000000..8d8e1f301d
--- /dev/null
+++ b/internal/errors/join.go
@@ -0,0 +1,53 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.20
+
+package errors
+
+// Join returns an error that wraps the given errors.
+// Any nil error values are discarded.
+// Join returns nil if errs contains no non-nil values.
+// The error formats as the concatenation of the strings obtained
+// by calling the Error method of each element of errs, with a newline
+// between each string.
+func Join(errs ...error) error {
+	n := 0
+	for _, err := range errs {
+		if err != nil {
+			n++
+		}
+	}
+	if n == 0 {
+		return nil
+	}
+	e := &joinError{
+		errs: make([]error, 0, n),
+	}
+	for _, err := range errs {
+		if err != nil {
+			e.errs = append(e.errs, err)
+		}
+	}
+	return e
+}
+
+type joinError struct {
+	errs []error
+}
+
+func (e *joinError) Error() string {
+	var b []byte
+	for i, err := range e.errs {
+		if i > 0 {
+			b = append(b, '\n')
+		}
+		b = append(b, err.Error()...)
+	}
+	return string(b)
+}
+
+func (e *joinError) Unwrap() []error {
+	return e.errs
+}
diff --git a/internal/errors/join_go1.20.go b/internal/errors/join_go1.20.go
new file mode 100644
index 0000000000..666f3c783e
--- /dev/null
+++ b/internal/errors/join_go1.20.go
@@ -0,0 +1,7 @@
+//go:build go1.20
+
+package errors
+
+import "errors"
+
+var Join = errors.Join
diff --git a/plugins/discovery/discovery.go b/plugins/discovery/discovery.go
index e322b5a835..550a2b4903 100644
--- a/plugins/discovery/discovery.go
+++ b/plugins/discovery/discovery.go
@@ -8,7 +8,6 @@ package discovery
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -23,6 +22,7 @@ import (
 	"github.com/open-policy-agent/opa/hooks"
 	bundleUtils "github.com/open-policy-agent/opa/internal/bundle"
 	cfg "github.com/open-policy-agent/opa/internal/config"
+	"github.com/open-policy-agent/opa/internal/errors"
 	"github.com/open-policy-agent/opa/keys"
 	"github.com/open-policy-agent/opa/logging"
 	"github.com/open-policy-agent/opa/metrics"
diff --git a/plugins/plugins.go b/plugins/plugins.go
index dcf65412da..ef4d31ceeb 100644
--- a/plugins/plugins.go
+++ b/plugins/plugins.go
@@ -7,7 +7,6 @@ package plugins
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"sync"
 	"time"
@@ -22,6 +21,7 @@ import (
 	"github.com/open-policy-agent/opa/hooks"
 	bundleUtils "github.com/open-policy-agent/opa/internal/bundle"
 	cfg "github.com/open-policy-agent/opa/internal/config"
+	"github.com/open-policy-agent/opa/internal/errors"
 	initload "github.com/open-policy-agent/opa/internal/runtime/init"
 	"github.com/open-policy-agent/opa/keys"
 	"github.com/open-policy-agent/opa/loader"