Straighten out remote.List{WithContext} (#1090)

remote.ListWithContext now just wraps remote.List, instead of the other
wawy around. This also has the effect that ping() uses the given
context.

remote.ListWithContext is marked as deprecated, to be removed in a
future update.

pkg/v1/remote/list.go

@@ -31,14 +31,16 @@ type tags struct {
 	Tags []string `json:"tags"`
 }
 
-// List wraps ListWithContext using the background context.
-func List(repo name.Repository, options ...Option) ([]string, error) {
-	return ListWithContext(context.Background(), repo, options...)
+// ListWithContext calls List with the given context.
+//
+// Deprecated: Use List and WithContext. This will be removed in a future release.
+func ListWithContext(ctx context.Context, repo name.Repository, options ...Option) ([]string, error) {
+	return List(repo, append(options, WithContext(ctx))...)
 }
 
-// ListWithContext calls /tags/list for the given repository, returning the list of tags
+// List calls /tags/list for the given repository, returning the list of tags
 // in the "tags" property.
-func ListWithContext(ctx context.Context, repo name.Repository, options ...Option) ([]string, error) {
+func List(repo name.Repository, options ...Option) ([]string, error) {
 	o, err := makeOptions(repo, options...)
 	if err != nil {
 		return nil, err
@@ -58,30 +60,22 @@ func ListWithContext(ctx context.Context, repo name.Repository, options ...Optio
 		RawQuery: "n=1000",
 	}
 
-	// This is lazy, but I want to make sure List(..., WithContext(ctx)) works
-	// without calling makeOptions() twice (which can have side effects).
-	// This means ListWithContext(ctx, ..., WithContext(ctx2)) prefers ctx2.
-	if o.context != context.Background() {
-		ctx = o.context
-	}
-
 	client := http.Client{Transport: tr}
 	tagList := []string{}
 	parsed := tags{}
 
 	// get responses until there is no next page
 	for {
 		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
+		case <-o.context.Done():
+			return nil, o.context.Err()
 		default:
 		}
 
-		req, err := http.NewRequest("GET", uri.String(), nil)
+		req, err := http.NewRequestWithContext(o.context, "GET", uri.String(), nil)
 		if err != nil {
 			return nil, err
 		}
-		req = req.WithContext(ctx)
 
 		resp, err := client.Do(req)
 		if err != nil {

pkg/v1/remote/list_test.go

@@ -20,6 +20,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -110,8 +111,8 @@ func TestCancelledList(t *testing.T) {
 	}
 
 	_, err = ListWithContext(ctx, repo)
-	if want, got := context.Canceled, err; got != want {
-		t.Errorf("wanted %v got %v", want, got)
+	if err == nil || !strings.Contains(err.Error(), "context canceled") {
+		t.Errorf(`unexpected error; want "context canceled", got %v`, err)
 	}
 }