18600: Support replacing dir with file using Splice().

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@curii.com>

diff --git a/sdk/go/arvados/fs_collection.go b/sdk/go/arvados/fs_collection.go
index afe92c991152c1aaf344fd9ebb0a04bb2bb82d67..0c5819721e0cb4e8762d6c1e1e3b70427a46a7da 100644 (file)
--- a/sdk/go/arvados/fs_collection.go
+++ b/sdk/go/arvados/fs_collection.go
@@ -1563,18 +1563,46 @@ func (dn *dirnode) snapshot() (*dirnode, error) {
 }
 
 func (dn *dirnode) Splice(repl inode) error {
-       repldn, ok := repl.(*dirnode)
-       if !ok {
-               return fmt.Errorf("cannot use Splice to replace a directory with a file: %w", ErrInvalidArgument)
-       }
-       repldn, err := repldn.snapshot()
+       repl, err := repl.Snapshot()
        if err != nil {
                return err
        }
-       dn.Lock()
-       defer dn.Unlock()
-       dn.inodes = repldn.inodes
-       dn.setTreeFS(dn.fs)
+       switch repl := repl.(type) {
+       default:
+               return fmt.Errorf("cannot splice snapshot containing %T: %w", repl, ErrInvalidArgument)
+       case *dirnode:
+               dn.Lock()
+               defer dn.Unlock()
+               dn.inodes = repl.inodes
+               dn.setTreeFS(dn.fs)
+       case *filenode:
+               dn.parent.Lock()
+               defer dn.parent.Unlock()
+               removing, err := dn.parent.Child(dn.fileinfo.name, nil)
+               if err != nil {
+                       return fmt.Errorf("cannot use Splice to replace a top-level directory with a file: %w", ErrInvalidOperation)
+               } else if removing != dn {
+                       // If ../thisdirname is not this dirnode, it
+                       // must be an inode that wraps a dirnode, like
+                       // a collectionFileSystem or deferrednode.
+                       if deferred, ok := removing.(*deferrednode); ok {
+                               // More useful to report the type of
+                               // the wrapped node rather than just
+                               // *deferrednode. (We know the real
+                               // inode is already loaded because dn
+                               // is inside it.)
+                               removing = deferred.realinode()
+                       }
+                       return fmt.Errorf("cannot use Splice to attach a file at top level of %T: %w", removing, ErrInvalidOperation)
+               }
+               dn.Lock()
+               defer dn.Unlock()
+               _, err = dn.parent.Child(dn.fileinfo.name, func(inode) (inode, error) { return repl, nil })
+               if err != nil {
+                       return err
+               }
+               repl.fs = dn.fs
+       }
        return nil
 }