[vpython] Enable base wheels, spec merging.

vpython/options.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 vpython
 
 import (
         "os"
 
         "golang.org/x/net/context"
@@ skipping 12 matching lines @@
 // Options is the set of options to use to construct and execute a VirtualEnv
 // Python application.
 type Options struct {
         // EnvConfig is the VirtualEnv configuration to run from.
         EnvConfig venv.Config
 
         // DefaultSpec is the default specification to use, if no specification was
         // supplied or probed.
         DefaultSpec vpython.Spec
 
+        // BaseWheels is the set of wheels to include in the spec. These will always
+        // be merged into the runtime spec and normalized, such that any duplicate
+        // wheels will be deduplicated.
+        BaseWheels []*vpython.Spec_Package
+
         // SpecLoader is the spec.Loader to use to load a specification file for a
         // given script.
         //
         // The empty value is a valid default spec.Loader.
         SpecLoader spec.Loader
 
         // Args are the arguments to forward to the Python process.
         Args []string
 
         // WaitForEnv, if true, means that if another agent holds a lock on the target
@@ skipping 22 matching lines @@
                 o.WorkDir = wd
         }
         if err := filesystem.AbsPath(&o.WorkDir); err != nil {
                 return errors.Annotate(err, "failed to resolve absolute path of WorkDir").Err()
         }
 
         // Resolve our target python script.
         if err := o.ResolveSpec(c); err != nil {
                 return errors.Annotate(err, "failed to resolve Python script").Err()
         }
+        if len(o.BaseWheels) > 0 {
+                o.EnvConfig.Spec = o.EnvConfig.Spec.Clone()
+                o.EnvConfig.Spec.Wheel = append(o.EnvConfig.Spec.Wheel, o.BaseWheels...)
+        }
 
         // If no environment base directory was supplied, create one under the current
         // working directory.
         if o.EnvConfig.BaseDir == "" {
                 // Is one specified in our environment?
                 if v, ok := o.Environ.Get(EnvironmentStampPathENV); ok {
                         var err error
                         if o.EnvConfig.BaseDir, err = venv.EnvRootFromStampPath(v); err != nil {
                                 return errors.Annotate(err, "failed to get env root from environment: %s", v).Err()
                         }
@@ skipping 64 matching lines @@
                 logging.Infof(c, "Loaded spec from environment: %s", v)
                 o.EnvConfig.Spec = &sp
                 return nil
         }
 
         // If standard resolution doesn't yield a spec, fall back on our default spec.
         logging.Infof(c, "Unable to resolve specification path. Using default specification.")
         o.EnvConfig.Spec = &o.DefaultSpec
         return nil
 }