Add UseFlex(c) for the cloud implementation.

impl/memory/context.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 memory
 
 import (
         "errors"
         "strings"
         "sync"
@@ skipping 78 matching lines @@
         for i := range *m {
                 (*m)[i].applyTxn(c, txnCtx[i])
         }
 }
 
 // Use calls UseWithAppID with the appid of "app"
 func Use(c context.Context) context.Context {
         return UseWithAppID(c, "dev~app")
 }
 
+// UseInfo adds an implementation for:
+//   * github.com/luci/gae/service/info
+// The application id wil be set to 'aid', and will not be modifiable in this
+// context. If 'aid' contains a "~" character, it will be treated as the
+// fully-qualified App ID and the AppID will be the string following the "~".
+func UseInfo(c context.Context, aid string) context.Context {
+        if c.Value(&memContextKey) != nil {
+                panic(errors.New("memory.Use: called twice on the same Context"))
+        }
+
+        fqAppID := aid
+        if parts := strings.SplitN(fqAppID, "~", 2); len(parts) == 2 {
+                aid = parts[1]
+        }
+
+        memctx := newMemContext(fqAppID)

[Vadim Sh., 2017/04/20 00:12:46]

this thing has mentions of datastore and task queues. "Info" service is,
supposedly, unrelated. I'm not sure what will happen if we return
half-initialized mem context.

I don't know this code very well... I think Robbie should review.

+        c = context.WithValue(c, &memContextKey, memctx)
+
+        return useGI(useGID(c, func(mod *globalInfoData) {
+                mod.appID = aid
+                mod.fqAppID = fqAppID
+        }))
+}
+
 // UseWithAppID adds implementations for the following gae services to the
 // context:
 //   * github.com/luci/gae/service/datastore
 //   * github.com/luci/gae/service/info
 //   * github.com/luci/gae/service/mail
 //   * github.com/luci/gae/service/memcache
 //   * github.com/luci/gae/service/taskqueue
 //   * github.com/luci/gae/service/user
 //   * github.com/luci/luci-go/common/logger (using memlogger)
 //
 // The application id wil be set to 'aid', and will not be modifiable in this
 // context. If 'aid' contains a "~" character, it will be treated as the
 // fully-qualified App ID and the AppID will be the string following the "~".
 //
 // These can be retrieved with the gae.Get functions.
 //
 // The implementations are all backed by an in-memory implementation, and start
 // with an empty state.
 //
 // Using this more than once per context.Context will cause a panic.
 func UseWithAppID(c context.Context, aid string) context.Context {
-        if c.Value(&memContextKey) != nil {
-                panic(errors.New("memory.Use: called twice on the same Context"))
-        }
         c = memlogger.Use(c)
-
-        fqAppID := aid
-        if parts := strings.SplitN(fqAppID, "~", 2); len(parts) == 2 {
-                aid = parts[1]
-        }
-
-        memctx := newMemContext(fqAppID)
-        c = context.WithValue(c, &memContextKey, memctx)
-        c = useGID(c, func(mod *globalInfoData) {
-                mod.appID = aid
-                mod.fqAppID = fqAppID
-        })
-        return useMod(useMail(useUser(useTQ(useRDS(useMC(useGI(c)))))))
+        c = UseInfo(c, aid) // Panics if UseWithAppID is called twice.
+        return useMod(useMail(useUser(useTQ(useRDS(useMC(c))))))
 }
 
 func cur(c context.Context) (*memContext, bool) {
         if txn := c.Value(&currentTxnKey); txn != nil {
                 // We are in a Transaction.
                 return txn.(*memContext), true
         }
         return c.Value(&memContextKey).(*memContext), false
 }
 
@@ skipping 57 matching lines @@
         if o != nil && o.Attempts != 0 {
                 attempts = o.Attempts
         }
         for attempt := 0; attempt < attempts; attempt++ {
                 if err := loopBody(attempt >= d.data.txnFakeRetry); err != ds.ErrConcurrentTransaction {
                         return err
                 }
         }
         return ds.ErrConcurrentTransaction
 }