tweak the Ls interface

1. Avoid `ipld.Link`. This is a protodag specific thing that will go away in
   future IPLD versions.
2. Avoid exposing the underlying file types. The user shouldn't care if they're
   dealing with a hamt, etc.
3. Add a field for a symlink's target.
4. Rename LsLink to DirEntry to better this type's role.

tests/unixfs.go

@@ -750,26 +750,25 @@ func (tp *provider) TestLs(t *testing.T) {
 		t.Error(err)
 	}
 
-	links, err := api.Unixfs().Ls(ctx, p)
+	entries, err := api.Unixfs().Ls(ctx, p)
 	if err != nil {
 		t.Error(err)
 	}
 
-	linkRes := <-links
-	if linkRes.Err != nil {
-		t.Fatal(linkRes.Err)
+	entry := <-entries
+	if entry.Err != nil {
+		t.Fatal(entry.Err)
 	}
-	link := linkRes.Link
-	if linkRes.Size != 15 {
-		t.Fatalf("expected size = 15, got %d", link.Size)
+	if entry.Size != 15 {
+		t.Fatalf("expected size = 15, got %d", entry.Size)
 	}
-	if link.Name != "name-of-file" {
-		t.Fatalf("expected name = name-of-file, got %s", link.Name)
+	if entry.Name != "name-of-file" {
+		t.Fatalf("expected name = name-of-file, got %s", entry.Name)
 	}
-	if link.Cid.String() != "QmX3qQVKxDGz3URVC3861Z3CKtQKGBn6ffXRBBWGMFz9Lr" {
-		t.Fatalf("expected cid = QmX3qQVKxDGz3URVC3861Z3CKtQKGBn6ffXRBBWGMFz9Lr, got %s", link.Cid)
+	if entry.Cid.String() != "QmX3qQVKxDGz3URVC3861Z3CKtQKGBn6ffXRBBWGMFz9Lr" {
+		t.Fatalf("expected cid = QmX3qQVKxDGz3URVC3861Z3CKtQKGBn6ffXRBBWGMFz9Lr, got %s", entry.Cid)
 	}
-	if l, ok := <-links; ok {
+	if l, ok := <-entries; ok {
 		t.Errorf("didn't expect a second link")
 		if l.Err != nil {
 			t.Error(l.Err)

unixfs.go

@@ -4,9 +4,8 @@ import (
 	"context"
 	"github.com/ipfs/interface-go-ipfs-core/options"
 
-	"github.com/ipfs/go-ipfs-files"
-	ipld "github.com/ipfs/go-ipld-format"
-	"github.com/ipfs/go-unixfs"
+	cid "github.com/ipfs/go-cid"
+	files "github.com/ipfs/go-ipfs-files"
 )
 
 type AddEvent struct {
@@ -16,21 +15,30 @@ type AddEvent struct {
 	Size  string       `json:",omitempty"`
 }
 
+// FileType is an enum of possible UnixFS file types.
 type FileType int32
 
 const (
-	TRaw       = FileType(unixfs.TRaw)
-	TFile      = FileType(unixfs.TFile)
-	TDirectory = FileType(unixfs.TDirectory)
-	TMetadata  = FileType(unixfs.TMetadata)
-	TSymlink   = FileType(unixfs.TSymlink)
-	THAMTShard = FileType(unixfs.THAMTShard)
+	// TUnknown means the file type isn't known (e.g., it hasn't been
+	// resolved).
+	TUnknown FileType = iota
+	// TFile is a regular file.
+	TFile
+	// TDirectory is a directory.
+	TDirectory
+	// TSymlink is a symlink.
+	TSymlink
 )
 
-type LsLink struct {
-	Link *ipld.Link
-	Size uint64
-	Type FileType
+// DirEntry is a directory entry returned by `Ls`.
+type DirEntry struct {
+	Name string
+	Cid  cid.Cid
+
+	// Only filled when asked to resolve the directory entry.
+	Size   uint64   // The size of the file in bytes (or the size of the symlink).
+	Type   FileType // The type of the file.
+	Target Path     // The symlink target (if a symlink).
 
 	Err error
 }
@@ -51,5 +59,5 @@ type UnixfsAPI interface {
 
 	// Ls returns the list of links in a directory. Links aren't guaranteed to be
 	// returned in order
-	Ls(context.Context, Path, ...options.UnixfsLsOption) (<-chan LsLink, error)
+	Ls(context.Context, Path, ...options.UnixfsLsOption) (<-chan DirEntry, error)
 }