[vpython] Add conditional packages based on PEP425

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"
         "sort"
 
         "github.com/luci/luci-go/vpython/api/vpython"
 
         "github.com/luci/luci-go/common/data/sortby"
         "github.com/luci/luci-go/common/errors"
 
         "github.com/golang/protobuf/proto"
 )
 
 // Render creates a human-readable string from spec.
 func Render(spec *vpython.Spec) string { return proto.MarshalTextString(spec) }
 
 // NormalizeEnvironment normalizes the supplied Environment such that two
 // messages with identical meaning will have identical representation.
 func NormalizeEnvironment(env *vpython.Environment) error {
         if env.Spec == nil {
                 env.Spec = &vpython.Spec{}
         }
-        if err := NormalizeSpec(env.Spec); err != nil {
+        if err := NormalizeSpec(env.Spec, env.Pep425Tag); err != nil {
                 return err
         }
 
         if env.Runtime == nil {
                 env.Runtime = &vpython.Runtime{}
         }
 
         sort.Sort(pep425TagSlice(env.Pep425Tag))
         return nil
 }
 
 // NormalizeSpec normalizes the specification Message such that two messages
 // with identical meaning will have identical representation.
-func NormalizeSpec(spec *vpython.Spec) error {
+//
+// NormalizeSpec will prune any Wheel entries that don't match the specified
+// tags, and will remove the match entries from any remaining Wheel entries.
+func NormalizeSpec(spec *vpython.Spec, tags []*vpython.Pep425Tag) error {
+        if spec.Virtualenv != nil && len(spec.Virtualenv.MatchTag) > 0 {
+                // The VirtualEnv package may not specify a match tag.
+                spec.Virtualenv.MatchTag = nil
+        }
+
+        // Apply match filters, prune any entries that don't match, and clear the
+        // MatchTag entries for those that do.
+        pos := 0
+        for _, wheel := range spec.Wheel {
+                if !PackageMatches(wheel, tags) {
+                        continue
+                }
+
+                wheel.MatchTag = nil
+                spec.Wheel[pos] = wheel
+                pos++
+        }
+        spec.Wheel = spec.Wheel[:pos]
+
         sort.Sort(specPackageSlice(spec.Wheel))
 
         // No duplicate packages. Since we're sorted, we can just check for no
         // immediate repetitions.
         for i, pkg := range spec.Wheel {
                 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()
                 }
@@ skipping 52 matching lines @@
 func (s pep425TagSlice) Len() int      { return len(s) }
 func (s pep425TagSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 
 func (s pep425TagSlice) Less(i, j int) bool {
         return sortby.Chain{
                 func(i, j int) bool { return s[i].Version < s[j].Version },
                 func(i, j int) bool { return s[i].Abi < s[j].Abi },
                 func(i, j int) bool { return s[i].Arch < s[j].Arch },
         }.Use(i, j)
 }