[errors] Greatly simplify common/errors package.

luci_config/server/cfgclient/backend/format/format.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 // Package format implements a config client Backend that performs formatting
 // on items.
 //
 // The available formats are registered during init() time via 'Register'.
 package format
 
@@ skipping 19 matching lines @@
 // Get implements backend.B.
 func (b *Backend) Get(c context.Context, configSet, path string, p backend.Params) (*backend.Item, error) {
         item, err := b.B.Get(c, configSet, path, p)
         if err != nil {
                 return nil, err
         }
 
         if !p.FormatSpec.Unformatted() {
                 formatter, err := getFormatter(p.FormatSpec.Formatter)
                 if err != nil {
-                        return nil, errors.Annotate(err).Reason("failed to get formatter for %(format)q").
-                                D("format", p.FormatSpec).Err()
+                        return nil, errors.Annotate(err, "failed to get formatter for %q", p.FormatSpec).Err()
                 }
 
                 if err := b.formatItem(item, formatter, p.FormatSpec); err != nil {
-                        return nil, errors.Annotate(err).Reason("failed to format item to %(format)q, data %(data)q").
-                                D("format", p.FormatSpec.Formatter).
-                                D("data", p.FormatSpec.Data).Err()
+                        return nil, errors.Annotate(err, "failed to format item to %q, data %q",
+                                p.FormatSpec.Formatter, p.FormatSpec.Data).Err()
                 }
         }
         return item, nil
 }
 
 // GetAll implements backend.B.
 func (b *Backend) GetAll(c context.Context, t backend.GetAllTarget, path string, p backend.Params) (
         []*backend.Item, error) {
 
         items, err := b.B.GetAll(c, t, path, p)
         if err != nil {
                 return nil, err
         }
 
         if !p.FormatSpec.Unformatted() {
                 formatter, err := getFormatter(p.FormatSpec.Formatter)
                 if err != nil {
-                        return nil, errors.Annotate(err).Reason("failed to get formatter for %(format)q, data %(data)q").
-                                D("format", p.FormatSpec.Formatter).
-                                D("data", p.FormatSpec.Data).Err()
+                        return nil, errors.Annotate(err, "failed to get formatter for %q, data %q",
+                                p.FormatSpec.Formatter, p.FormatSpec.Data).Err()
                 }
 
                 lme := errors.NewLazyMultiError(len(items))
                 for i, item := range items {
                         if err := b.formatItem(item, formatter, p.FormatSpec); err != nil {
                                 lme.Assign(i, err)
                         }
                 }
 
                 if err := lme.Get(); err != nil {
-                        return nil, errors.Annotate(err).Reason("failed to format items to %(format)q, data %(data)q").
-                                D("format", p.FormatSpec.Formatter).
-                                D("data", p.FormatSpec.Data).Err()
+                        return nil, errors.Annotate(err, "failed to format items to %q, data %q",
+                                p.FormatSpec.Formatter, p.FormatSpec.Data).Err()
                 }
         }
         return items, nil
 }
 
 func (b *Backend) formatItem(it *backend.Item, formatter Formatter, fs backend.FormatSpec) error {
         if !it.FormatSpec.Unformatted() {
                 // Item is already formatted.
                 return nil
         }
 
         // Item is not formatted, so format it.
         content, err := formatter.FormatItem(it.Content, fs.Data)
         if err != nil {
-                return errors.Annotate(err).Reason("failed to format item").Err()
+                return errors.Annotate(err, "failed to format item").Err()
         }
         it.Content = content
         it.FormatSpec = fs
         return nil
 }