[errors] Greatly simplify common/errors package.

appengine/datastorecache/manager.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 datastorecache
 
 import (
-        "bytes"
         "fmt"
         "net/http"
         "strings"
         "sync/atomic"
         "time"
 
         "github.com/luci/luci-go/appengine/memlock"
         "github.com/luci/luci-go/common/clock"
         "github.com/luci/luci-go/common/errors"
         log "github.com/luci/luci-go/common/logging"
@@ skipping 15 matching lines @@
                         return
                 }
 
                 // Handler returned an error, dump it to output.
                 ctx.Writer.WriteHeader(http.StatusInternalServerError)
 
                 // Log all of our stack lines individually, so we don't overflow the
                 // maximum log message size with a full stack.
                 stk := errors.RenderStack(err)
                 log.WithError(err).Errorf(ctx.Context, "Handler returned error.")
-                for _, line := range stk.ToLines() {
+                for _, line := range stk {
                         log.Errorf(ctx.Context, ">> %s", line)
                 }
 
                 dumpErr := func() error {
-                        var buf bytes.Buffer
-                        if _, err := stk.DumpTo(&buf); err != nil {
-                                return err
-                        }
-                        if _, err := buf.WriteTo(ctx.Writer); err != nil {
-                                return err
+                        for _, line := range stk {
+                                if _, err := ctx.Writer.Write([]byte(line + "\n")); err != nil {
+                                        return err
+                                }
                         }
                         return nil
                 }()
                 if dumpErr != nil {
                         log.WithError(dumpErr).Errorf(ctx.Context, "Failed to dump error stack.")
                 }
         }
 }
 
 // manager is initialized to perform the management cron task.
@@ skipping 76 matching lines @@
                         if rv == nil {
                                 ms.st.LastSuccessfulRun = ms.now
                         }
 
                         if rv := datastore.Put(c, &ms.st); rv != nil {
                                 log.WithError(rv).Errorf(c, "Failed to Put() stats on completion.")
                         }
                 }()
 
                 if err := ms.runLocked(c); err != nil {
-                        return errors.Annotate(err).Err()
+                        return errors.Annotate(err, "running maintenance loop").Err()
                 }
 
                 // If we observed errors during processing, note this.
                 if ms.errors > 0 {
-                        return errors.Reason("%(count)d error(s) encountered during processing").D("count", ms.errors).Err()
+                        return errors.Reason("%d error(s) encountered during processing", ms.errors).Err()
                 }
                 return nil
         })
 }
 
 // runLocked runs the main main maintenance loop.
 //
 // As the run is executed, stats can be collected in ms.st. These will be output
 // to datastore on completion.
 func (ms *managerShard) runLocked(c context.Context) error {
@@ skipping 156 matching lines @@
                 Size:     ms.queryBatchSize,
                 Callback: handleEntries,
         }
         err := b.Run(c, q, func(e *entry) error {
                 totalEntries++
                 ms.observeEntry()
                 entries = append(entries, e)
                 return nil
         })
         if err != nil {
-                return errors.Annotate(err).Reason("failed to run entry query").Err()
+                return errors.Annotate(err, "failed to run entry query").Err()
         }
 
         // Flush any outstanding entries (ignore error, will always be nil).
         _ = handleEntries(c)
         if totalErrors > 0 {
                 ms.observeErrors(totalErrors)
         }
 
         log.Fields{
                 "entries":   totalEntries,
                 "errors":    totalErrors,
                 "refreshed": totalRefreshed,
                 "pruned":    totalPruned,
         }.Infof(c, "Successfully updated cache entries.")
         return nil
 }