libfuse: on macOS, delete a moved node from the nodes cache

Otherwise, the kernel might still treat it as having the old parent
ID.

This shouldn't mess up any kernel caching or libkbfs garbage
collection, since if the original node for the moved node is still in
use, bazil.org would hold a reference to it.

But it's definitely a little weird that the same node might have two
inodes pointing into it.  We should remove this once the osxfuse issue
is fixed.

Issue: #1881
Issue: KBFS-3576
Issue: macfuse/macfuse#553

libfuse/dir.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"math"
 	"os"
+	"runtime"
 	"strings"
 	"sync"
 	"syscall"
@@ -731,6 +732,22 @@ func (d *Dir) Rename(ctx context.Context, req *fuse.RenameRequest,
 
 	switch e := err.(type) {
 	case nil:
+		// Because of https://github.com/osxfuse/osxfuse/issues/553, a
+		// node that's moved to a different directory needs to get a
+		// new Node object (and inode) on the next lookup.  The
+		// easiest way to do that is to remove the moved node from
+		// this folder's local cache. See KBFS-3576.
+		if runtime.GOOS == "darwin" &&
+			d.node.GetID() != realNewDir.node.GetID() {
+			movedNode, _, err := d.folder.fs.config.KBFSOps().Lookup(
+				ctx, realNewDir.node, req.NewName)
+			if err == nil {
+				d.folder.nodesMu.Lock()
+				delete(d.folder.nodes, movedNode.GetID())
+				d.folder.nodesMu.Unlock()
+			}
+		}
+
 		return nil
 	case libkbfs.RenameAcrossDirsError:
 		var execPathErr error

libfuse/mount_test.go

@@ -3931,7 +3931,8 @@ func TestInodes(t *testing.T) {
 	syncFilename(t, p2)
 
 	inode2 := getInode(p2)
-	if inode != inode2 {
+	if runtime.GOOS != "darwin" && inode != inode2 {
+		// (See KBFS-3576 for the darwin restriction here.)
 		t.Fatalf("Inode changed after rename: %d vs %d", inode, inode2)
 	}