From 758038a6f3676beaa11d9a1d435fc8366d8fb380 Mon Sep 17 00:00:00 2001
From: Steve Coffman <steve@khanacademy.org>
Date: Sun, 12 Mar 2023 17:50:50 -0400
Subject: [PATCH] Add Go 1.20 errors.Join support

Signed-off-by: Steve Coffman <steve@khanacademy.org>
---
 go.mod  |  2 +-
 join.go | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 join.go

diff --git a/go.mod b/go.mod
index 5c32a5d..defdc21 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/cockroachdb/errors
 
-go 1.17
+go 1.20
 
 require (
 	github.com/cockroachdb/datadriven v1.0.2
diff --git a/join.go b/join.go
new file mode 100644
index 0000000..30f78a5
--- /dev/null
+++ b/join.go
@@ -0,0 +1,63 @@
+package errors
+
+import (
+	"fmt"
+)
+
+// 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
+}
+
+func (e *joinError) Format(w fmt.State, verb rune) {
+	for i, err := range e.Unwrap() {
+		if i > 0 {
+			fmt.Fprint(w, "\n")
+		}
+		fmt.Fprintf(w, "[%d]:\n  ", i)
+		s := fmt.Sprintf(fmt.FormatString(w, verb), err)
+		s = strings.Join(strings.Split(s, "\n"), "\n  ")
+		fmt.Fprint(w, s)
+	}
+}