Remove *App from Apk type

This circular data flow was preventing serialization, useful for caching
into disk.

cmd/fdroidcl/download.go

@@ -40,7 +40,7 @@ func downloadApk(apk *fdroidcl.Apk) string {
 	url := apk.URL()
 	path := apkPath(apk.ApkName)
 	if err := downloadEtag(url, path, apk.Hash.Data); err != nil {
-		log.Fatalf("Could not download %s: %v", apk.App.ID, err)
+		log.Fatalf("Could not download %s: %v", apk.AppID, err)
 	}
 	return path
 }

cmd/fdroidcl/install.go

@@ -55,10 +55,10 @@ func downloadAndDo(apps []*fdroidcl.App, device *adb.Device, doApk func(*adb.Dev
 }
 
 func installApk(device *adb.Device, apk *fdroidcl.Apk, path string) {
-	fmt.Printf("Installing %s... ", apk.App.ID)
+	fmt.Printf("Installing %s... ", apk.AppID)
 	if err := device.Install(path); err != nil {
 		fmt.Println()
-		log.Fatalf("Could not install %s: %v", apk.App.ID, err)
+		log.Fatalf("Could not install %s: %v", apk.AppID, err)
 	}
 	fmt.Println("done")
 }

cmd/fdroidcl/upgrade.go

@@ -44,10 +44,10 @@ func runUpgrade(args []string) {
 }
 
 func upgradeApk(device *adb.Device, apk *fdroidcl.Apk, path string) {
-	fmt.Printf("Upgrading %s... ", apk.App.ID)
+	fmt.Printf("Upgrading %s... ", apk.AppID)
 	if err := device.Upgrade(path); err != nil {
 		fmt.Println()
-		log.Fatalf("Could not upgrade %s: %v", apk.App.ID, err)
+		log.Fatalf("Could not upgrade %s: %v", apk.AppID, err)
 	}
 	fmt.Println("done")
 }

index.go

@@ -86,7 +86,7 @@ func (a *App) IconURLForDensity(density IconDensity) string {
 	if len(a.Apks) == 0 {
 		return ""
 	}
-	return fmt.Sprintf("%s/%s/%s", a.Apks[0].Repo.URL,
+	return fmt.Sprintf("%s/%s/%s", a.Apks[0].repo.URL,
 		getIconsDir(density), a.Icon)
 }
 
@@ -195,16 +195,16 @@ type Apk struct {
 	Feats   CommaList `xml:"features"`
 	Hash    HexHash   `xml:"hash"`
 
-	App  *App  `xml:"-"`
-	Repo *Repo `xml:"-"`
+	AppID string `xml:"-"`
+	repo  *Repo  `xml:"-"`
 }
 
 func (a *Apk) URL() string {
-	return fmt.Sprintf("%s/%s", a.Repo.URL, a.ApkName)
+	return fmt.Sprintf("%s/%s", a.repo.URL, a.ApkName)
 }
 
 func (a *Apk) SrcURL() string {
-	return fmt.Sprintf("%s/%s", a.Repo.URL, a.SrcName)
+	return fmt.Sprintf("%s/%s", a.repo.URL, a.SrcName)
 }
 
 func (a *Apk) IsCompatibleABI(ABIs []string) bool {
@@ -259,8 +259,8 @@ func LoadIndexXML(r io.Reader) (*Index, error) {
 		sort.Sort(ApkList(app.Apks))
 		for j := range app.Apks {
 			apk := &app.Apks[j]
-			apk.App = app
-			apk.Repo = &index.Repo
+			apk.AppID = app.ID
+			apk.repo = &index.Repo
 		}
 	}
 	return &index, nil