consumererror: Add partial error type

This PR adds functionality for consumers to create a partial error type.
This will allow consumers to properly report partial success/failure with
failed item counts, which can subsequently be used when reporting
sent/failed metrics.

Author: braydonk

consumer/consumererror/partial.go

@@ -0,0 +1,44 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package consumererror // import "go.opentelemetry.io/collector/consumer/consumererror"
+
+import "errors"
+
+type partialError struct {
+	inner  error
+	failed int
+}
+
+var _ error = partialError{}
+
+func (pe partialError) Error() string {
+	return pe.inner.Error()
+}
+
+func (pe partialError) Unwrap() error {
+	return pe.inner
+}
+
+func (pe partialError) Failed() int {
+	return pe.failed
+}
+
+// NewPartial creates a new partial error. This is used by consumers
+// to report errors where only a subset of the total items failed
+// to be written, but it is not possible to tell which particular items
+// failed.
+func NewPartial(err error, failed int) error {
+	return NewPermanent(partialError{
+		inner:  err,
+		failed: failed,
+	})
+}
+
+// AsPartial checks if an error was wrapped with the NewPartial function,
+// or if it contains one such error in its Unwrap() tree.
+func AsPartial(err error) (partialError, bool) {
+	var pe partialError
+	ok := errors.As(err, &pe)
+	return pe, ok
+}

consumer/consumererror/partial_test.go

@@ -0,0 +1,19 @@
+package consumererror
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPartial(t *testing.T) {
+	internalErr := errors.New("some points failed")
+	err := NewPartial(internalErr, 5)
+	assert.True(t, IsPermanent(err))
+	partialErr, ok := AsPartial(err)
+	assert.True(t, ok)
+	assert.Equal(t, 5, partialErr.Failed())
+	assert.Equal(t, internalErr, partialErr.Unwrap())
+	assert.Equal(t, internalErr.Error(), partialErr.Error())
+}