[errors] de-specialize Transient in favor of Tags.

server/settings/admin/handlers.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 admin implements HTTP routes for settings UI.
 package admin
 
 import (
         "html/template"
         "net"
         "net/http"
 
         "golang.org/x/net/context"
 
         "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
+        "github.com/luci/luci-go/common/retry/transient"
 
         "github.com/luci/luci-go/server/auth"
         "github.com/luci/luci-go/server/auth/authdb"
         "github.com/luci/luci-go/server/auth/identity"
         "github.com/luci/luci-go/server/auth/xsrf"
         "github.com/luci/luci-go/server/router"
         "github.com/luci/luci-go/server/templates"
 
         "github.com/luci/luci-go/server/settings/admin/internal/assets"
 )
@@ skipping 40 matching lines @@
         ))
 
         rr.GET("", router.MiddlewareChain{}, indexPage)
         rr.GET("/:SettingsKey", router.MiddlewareChain{}, settingsPageGET)
         rr.POST("/:SettingsKey", router.NewMiddlewareChain(xsrf.WithTokenCheck), settingsPagePOST)
 }
 
 // replyError sends HTML error page with status 500 on transient errors or 400
 // on fatal ones.
 func replyError(c context.Context, rw http.ResponseWriter, err error) {
-        if errors.IsTransient(err) {
+        if transient.Tag.In(err) {
                 rw.WriteHeader(http.StatusInternalServerError)
         } else {
                 rw.WriteHeader(http.StatusBadRequest)
         }
         templates.MustRender(c, rw, "pages/error.html", templates.Args{
                 "Error": err.Error(),
         })
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ skipping 40 matching lines @@
         // Redirect anonymous users to a login page that redirects back to the current
         // page.
         if u.Identity == identity.AnonymousIdentity {
                 // Make the current URL relative to the host.
                 destURL := *c.Request.URL
                 destURL.Host = ""
                 destURL.Scheme = ""
                 url, err := auth.LoginURL(c.Context, destURL.String())
                 if err != nil {
                         logging.WithError(err).Errorf(c.Context, "Error when generating login URL")
-                        if errors.IsTransient(err) {
+                        if transient.Tag.In(err) {
                                 http.Error(c.Writer, "Transient error when generating login URL, see logs", 500)
                         } else {
                                 http.Error(c.Writer, "Can't generate login URL, see logs", 401)
                         }
                         return
                 }
                 http.Redirect(c.Writer, c.Request, url, 302)
                 return
         }
 
         // Non anonymous users must be admins to proceed.
         if !u.Superuser {
                 c.Writer.WriteHeader(http.StatusForbidden)
                 templates.MustRender(c.Context, c.Writer, "pages/access_denied.html", nil)
                 return
         }
 
         next(c)
 }