[errors] Greatly simplify common/errors package.

logdog/client/cmd/logdog_butler/main.go

 // Copyright 2015 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 main
 
 import (
-        "bytes"
         "flag"
         "fmt"
         "net/http"
         "os"
         "os/signal"
         "sort"
         "strings"
         "time"
 
         "github.com/maruel/subcommands"
@@ skipping 191 matching lines @@
         return nil
 }
 
 // logAnnotatedErr logs the full stack trace from an annotated error to the
 // installed logger at error level.
 func logAnnotatedErr(ctx context.Context, err error, f string, args ...interface{}) {
         if err == nil {
                 return
         }
 
-        var buf bytes.Buffer
-        st := errors.RenderStack(err)
-        if _, derr := st.DumpTo(&buf); derr != nil {
-                // This can't really fail, since we're rendering to a Buffer.
-                panic(derr)
-        }
-
         nargs := make([]interface{}, len(args)+1)
-        nargs[copy(nargs, args)] = buf.Bytes()
+        nargs[copy(nargs, args)] = strings.Join(errors.RenderStack(err), "\n")
 
         if f == "" {
                 f = "Captured error stack:"
         }
         log.Errorf(ctx, f+"\n%s", nargs...)
 }
 
 func mainImpl(ctx context.Context, defaultAuthOpts auth.Options, argv []string) int {
         defaultAuthOpts.Scopes = allOutputScopes()
 
@@ skipping 113 matching lines @@
 
         paniccatcher.Do(func() {
                 rc = mainImpl(ctx, chromeinfra.DefaultAuthOptions(), os.Args[1:])
         }, func(p *paniccatcher.Panic) {
                 log.Fields{
                         "panic.error": p.Reason,
                 }.Errorf(ctx, "Panic caught in main:\n%s", p.Stack)
                 rc = runtimeErrorReturnCode
         })
 }