[errors] Greatly simplify common/errors package.

milo/build_source/swarming/buildinfo.go

 // Copyright 2017 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 swarming
 
 import (
         "strconv"
         "strings"
         "unicode/utf8"
@@ skipping 202 matching lines @@
         switch {
         case luciProject == "":
                 return nil, errors.New("no 'luci_project' tag")
         case logLocation == "":
                 return nil, errors.New("no 'log_location' tag")
         }
 
         // Gather our Swarming task template parameters and perform a substitution.
         runID, err := getRunID(taskID, tryNumber)
         if err != nil {
-                return nil, errors.Annotate(err).Err()
+                return nil, errors.Annotate(err, "").Err()
         }
         p := tasktemplate.Params{
                 SwarmingRunID: runID,
         }
         if logLocation, err = p.Resolve(logLocation); err != nil {
-                return nil, errors.Annotate(err).Reason("failed to resolve swarming task templating in 'log_location'").Err()
+                return nil, errors.Annotate(err, "failed to resolve swarming task templating in 'log_location'").Err()
         }
 
         addr, err := types.ParseURL(logLocation)
         if err != nil {
-                return nil, errors.Annotate(err).Reason("could not parse LogDog stream from location").Err()
+                return nil, errors.Annotate(err, "could not parse LogDog stream from location").Err()
         }
 
         // The LogDog stream's project should match the LUCI project.
         if string(addr.Project) != luciProject {
-                return nil, errors.Reason("stream project %(streamProject)q doesn't match LUCI project %(luciProject)q").
-                        D("luciProject", luciProject).
-                        D("streamProject", addr.Project).
-                        Err()
+                return nil, errors.Reason("stream project %q doesn't match LUCI project %q", addr.Project, luciProject).Err()
         }
 
         return addr, nil
 }
 
 // getRunID converts a Swarming task ID and try number into a Swarming Run ID.
 //
 // The run ID is a permutation of the last four bits of the Swarming Task ID.
 // Therefore, we chop it off of the string, mutate it, and then add it back.
 //
 // TODO(dnj): Replace this with Swarming API call once finished.
 func getRunID(taskID string, tryNumber int64) (string, error) {
         // Slice off the last character form the task ID.
         if len(taskID) == 0 {
                 return "", errors.New("swarming task ID is empty")
         }
 
         // Parse "tryNumber" as a hex string.
         if tryNumber < 0 || tryNumber > 0x0F {
-                return "", errors.Reason("try number %(try)d exceeds 4 bits").
-                        D("try", tryNumber).
-                        Err()
+                return "", errors.Reason("try number %d exceeds 4 bits", tryNumber).Err()
         }
 
         lastChar, lastCharSize := utf8.DecodeLastRuneInString(taskID)
         v, err := strconv.ParseUint(string(lastChar), 16, 8)
         if err != nil {
-                return "", errors.Annotate(err).Reason("failed to parse hex from rune: %(rune)r").
-                        D("rune", lastChar).
-                        Err()
+                return "", errors.Annotate(err, "failed to parse hex from rune: %r", lastChar).Err()
         }
 
         return taskID[:len(taskID)-lastCharSize] + strconv.FormatUint((v|uint64(tryNumber)), 16), nil
 }