Subscriptions: Fix all asset subs erroring on no enabled assets

Only subs with Empty asset should do anything when assets are empty.
If asset is set to all and no assets are enabled, we should return
nothing

exchanges/bitmex/bitmex_test.go

@@ -1127,6 +1127,12 @@ func TestGenerateSubscriptions(t *testing.T) {
 	subs, err := b.generateSubscriptions()
 	require.NoError(t, err, "generateSubscriptions must not error")
 	testsubs.EqualLists(t, exp, subs)
+
+	for _, a := range b.GetAssetTypes(true) {
+		b.CurrencyPairs.SetAssetEnabled(a, false)
+	}
+	_, err = b.generateSubscriptions()
+	require.NoError(t, err, "generateSubscriptions must not error when no assets are enabled")
 }
 
 func TestSubscribe(t *testing.T) {

exchanges/bitmex/bitmex_websocket.go

@@ -650,16 +650,16 @@ func channelName(s *subscription.Subscription, a asset.Item) string {
 
 const subTplText = `
 {{- if $.S.Asset }}
-	{{ range $asset, $pairs := $.AssetPairs }}
+	{{- range $asset, $pairs := $.AssetPairs }}
 		{{- with $name := channelName $.S $asset }}
-			{{- range $i, $p := $pairs -}}
-				{{- $name -}} : {{- $p -}}
-				{{ $.PairSeparator }}
+			{{- range $i, $p := $pairs }}
+				{{- $name -}} : {{- $p }}
+				{{- $.PairSeparator }}
 			{{- end }}
 		{{- end }}
-		{{ $.AssetSeparator }}
+		{{- $.AssetSeparator }}
 	{{- end }}
-{{- else -}}
-	{{ channelName $.S $.S.Asset }}
+{{- else }}
+	{{- channelName $.S $.S.Asset }}
 {{- end }}
 `

exchanges/subscription/template.go

@@ -114,15 +114,18 @@ func expandTemplate(e iExchange, s *Subscription, ap assetPairs, assets asset.It
 	switch s.Asset {
 	case asset.All:
 		subCtx.AssetPairs = ap
+		if len(ap) == 0 {
+			return List{}, nil // Nothing is enabled for any asset, only deliberately Empty asset subs can proceed
+		}
 	default:
+		if s.Asset != asset.Empty && len(ap[s.Asset]) == 0 {
+			return List{}, nil // Nothing is enabled for this sub asset
+		}
 		// This deliberately includes asset.Empty to harmonise handling
 		subCtx.AssetPairs = assetPairs{
 			s.Asset: ap[s.Asset],
 		}
 		assets = asset.Items{s.Asset}
-		if s.Asset != asset.Empty && len(ap[s.Asset]) == 0 {
-			return List{}, nil // Nothing is enabled for this sub asset
-		}
 	}
 
 	buf := &bytes.Buffer{}