[vpython] Incorporate interpreter path/hash.

vpython/spec/spec.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 spec
 
 import (
         "crypto/sha256"
         "encoding/hex"
         "fmt"
@@ skipping 25 matching lines @@
                 if i > 0 && pkg.Name == spec.Wheel[i-1].Name {
                         return errors.Reason("duplicate spec entries for package %(path)q").
                                 D("name", pkg.Name).
                                 Err()
                 }
         }
 
         return nil
 }
 
-// Hash hashes the contents of the supplied "spec" and returns the result as
-// a hex-encoded string.
+// Hash hashes the contents of the supplied "spec" and "rt" and returns the
+// result as a hex-encoded string.
 //
 // If not empty, the contents of extra are prefixed to hash string. This can
 // be used to factor additional influences into the spec hash.
-func Hash(spec *vpython.Spec, extra string) string {
-        data, err := proto.Marshal(spec)
-        if err != nil {
-                panic(fmt.Errorf("failed to marshal proto: %v", err))
+func Hash(spec *vpython.Spec, rt *vpython.Runtime, extra string) string {
+        mustMarshal := func(msg proto.Message) []byte {
+                data, err := proto.Marshal(msg)
+                if err != nil {
+                        panic(fmt.Errorf("failed to marshal proto: %v", err))
+                }
+                return data
         }
+        specData := mustMarshal(spec)
+        rtData := mustMarshal(rt)
 
         mustWrite := func(v int, err error) {
                 if err != nil {
                         panic(fmt.Errorf("impossible: %s", err))
                 }
         }
 
         hash := sha256.New()
         if extra != "" {
                 mustWrite(fmt.Fprintf(hash, "%s:", extra))
         }
         mustWrite(fmt.Fprintf(hash, "%s:", vpython.Version))
-        mustWrite(hash.Write(data))
+        mustWrite(hash.Write(specData))
+        mustWrite(hash.Write([]byte(":")))
+        mustWrite(hash.Write(rtData))
         return hex.EncodeToString(hash.Sum(nil))
 }
 
 type specPackageSlice []*vpython.Spec_Package
 
 func (s specPackageSlice) Len() int      { return len(s) }
 func (s specPackageSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 
 func (s specPackageSlice) Less(i, j int) bool {
         return sortby.Chain{
                 func(i, j int) bool { return s[i].Name < s[j].Name },
                 func(i, j int) bool { return s[i].Version < s[j].Version },
         }.Use(i, j)
 }