move implementation to internal/ directory (#828)

internal/util/errorarray/errorarray.go

@@ -0,0 +1,43 @@
+package errorarray
+
+import (
+	"fmt"
+	"strings"
+)
+
+type Errors struct {
+	Msg     string
+	Wrapped []error
+}
+
+var _ error = (*Errors)(nil)
+
+func Wrap(errs []error, msg string) Errors {
+	if len(errs) == 0 {
+		panic("passing empty errs argument")
+	}
+	return Errors{Msg: msg, Wrapped: errs}
+}
+
+func (e Errors) Unwrap() error {
+	if len(e.Wrapped) == 1 {
+		return e.Wrapped[0]
+	}
+	return nil // ... limitation of the Go 1.13 errors API
+}
+
+func (e Errors) Error() string {
+	if len(e.Wrapped) == 1 {
+		return fmt.Sprintf("%s: %s", e.Msg, e.Wrapped[0])
+	}
+	var buf strings.Builder
+	fmt.Fprintf(&buf, "%s: multiple errors:\n", e.Msg)
+	for i, err := range e.Wrapped {
+		fmt.Fprintf(&buf, "%s", err)
+		if i != len(e.Wrapped)-1 {
+			fmt.Fprintf(&buf, "\n")
+		}
+	}
+	return buf.String()
+
+}