node/basic: add Chooser

Fixes #185.

node/basic/any.go

@@ -11,6 +11,20 @@ var (
 	//_ ipld.NodeAssembler = &anyAssembler{}
 )
 
+// Note that we don't use a "var _" declaration to assert that Chooser
+// implements traversal.LinkTargetNodePrototypeChooser, to keep basicnode's
+// dependencies fairly light.
+
+// Chooser implements traversal.LinkTargetNodePrototypeChooser.
+//
+// It can be used directly when loading links into the "any" prototype,
+// or with another chooser layer on top, such as:
+//
+//    prototypeChooser := dagpb.AddSupportToChooser(basicnode.Chooser)
+func Chooser(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
+	return Prototype__Any{}, nil
+}
+
 // anyNode is a union meant for alloc amortization; see anyAssembler.
 // Note that anyBuilder doesn't use anyNode, because it's not aiming to amortize anything.
 //

traversal/focus_test.go

@@ -136,10 +136,8 @@ func TestFocusWithLinkLoading(t *testing.T) {
 		lsys.StorageReadOpener = (&store).OpenRead
 		err := traversal.Progress{
 			Cfg: &traversal.Config{
-				LinkSystem: lsys,
-				LinkTargetNodePrototypeChooser: func(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
-					return basicnode.Prototype__Any{}, nil
-				},
+				LinkSystem:                     lsys,
+				LinkTargetNodePrototypeChooser: basicnode.Chooser,
 			},
 		}.Focus(rootNode, ipld.ParsePath("linkedMap/nested/nonlink"), func(prog traversal.Progress, n ipld.Node) error {
 			Wish(t, n, ShouldEqual, basicnode.NewString("zoo"))
@@ -168,10 +166,8 @@ func TestGetWithLinkLoading(t *testing.T) {
 		lsys.StorageReadOpener = (&store).OpenRead
 		n, err := traversal.Progress{
 			Cfg: &traversal.Config{
-				LinkSystem: lsys,
-				LinkTargetNodePrototypeChooser: func(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
-					return basicnode.Prototype__Any{}, nil
-				},
+				LinkSystem:                     lsys,
+				LinkTargetNodePrototypeChooser: basicnode.Chooser,
 			},
 		}.Get(rootNode, ipld.ParsePath("linkedMap/nested/nonlink"))
 		Wish(t, err, ShouldEqual, nil)
@@ -312,10 +308,8 @@ func TestFocusedTransformWithLinks(t *testing.T) {
 	lsys.StorageReadOpener = (&store).OpenRead
 	lsys.StorageWriteOpener = (&store2).OpenWrite
 	cfg := traversal.Config{
-		LinkSystem: lsys,
-		LinkTargetNodePrototypeChooser: func(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
-			return basicnode.Prototype.Any, nil
-		},
+		LinkSystem:                     lsys,
+		LinkTargetNodePrototypeChooser: basicnode.Chooser,
 	}
 	t.Run("UpdateMapBeyondLink", func(t *testing.T) {
 		n, err := traversal.Progress{

traversal/walk_test.go

@@ -122,10 +122,8 @@ func TestWalkMatching(t *testing.T) {
 		lsys.StorageReadOpener = (&store).OpenRead
 		err = traversal.Progress{
 			Cfg: &traversal.Config{
-				LinkSystem: lsys,
-				LinkTargetNodePrototypeChooser: func(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
-					return basicnode.Prototype__Any{}, nil
-				},
+				LinkSystem:                     lsys,
+				LinkTargetNodePrototypeChooser: basicnode.Chooser,
 			},
 		}.WalkMatching(middleMapNode, s, func(prog traversal.Progress, n ipld.Node) error {
 			switch order {
@@ -168,10 +166,8 @@ func TestWalkMatching(t *testing.T) {
 		lsys.StorageReadOpener = (&store).OpenRead
 		err = traversal.Progress{
 			Cfg: &traversal.Config{
-				LinkSystem: lsys,
-				LinkTargetNodePrototypeChooser: func(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
-					return basicnode.Prototype__Any{}, nil
-				},
+				LinkSystem:                     lsys,
+				LinkTargetNodePrototypeChooser: basicnode.Chooser,
 			},
 		}.WalkMatching(middleListNode, s, func(prog traversal.Progress, n ipld.Node) error {
 			switch order {
@@ -213,10 +209,8 @@ func TestWalkMatching(t *testing.T) {
 		lsys.StorageReadOpener = (&store).OpenRead
 		err = traversal.Progress{
 			Cfg: &traversal.Config{
-				LinkSystem: lsys,
-				LinkTargetNodePrototypeChooser: func(_ ipld.Link, _ ipld.LinkContext) (ipld.NodePrototype, error) {
-					return basicnode.Prototype__Any{}, nil
-				},
+				LinkSystem:                     lsys,
+				LinkTargetNodePrototypeChooser: basicnode.Chooser,
 			},
 		}.WalkMatching(rootNode, s, func(prog traversal.Progress, n ipld.Node) error {
 			switch order {