packer: MultiError to represent multiple errors

packer/multi_error.go

@@ -0,0 +1,24 @@
+package packer
+
+import (
+	"fmt"
+	"strings"
+)
+
+// MultiError is an error type to track multiple errors. This is used to
+// accumulate errors in cases such as configuration parsing, and returning
+// them as a single error.
+type MultiError struct {
+	Errors []error
+}
+
+func (e *MultiError) Error() string {
+	points := make([]string, len(e.Errors))
+	for i, err := range e.Errors {
+		points[i] = fmt.Sprintf("* %s", err)
+	}
+
+	return fmt.Sprintf(
+		"%d error(s) occurred:\n\n%s",
+		len(e.Errors), strings.Join(points, "\n"))
+}

packer/multi_error_test.go

@@ -0,0 +1,32 @@
+package packer
+
+import (
+	"cgl.tideland.biz/asserts"
+	"errors"
+	"testing"
+)
+
+func TestMultiError_Impl(t *testing.T) {
+	var raw interface{}
+	raw = &MultiError{}
+	if _, ok := raw.(error); !ok {
+		t.Fatal("MultiError must implement error")
+	}
+}
+
+func TestMultiErrorError(t *testing.T) {
+	assert := asserts.NewTestingAsserts(t, true)
+
+	expected := `2 error(s) occurred:
+
+* foo
+* bar`
+
+	errors := []error{
+		errors.New("foo"),
+		errors.New("bar"),
+	}
+
+	multi := &MultiError{errors}
+	assert.Equal(multi.Error(), expected, "should have proper error")
+}