3 files changed, 39 insertions, 5 deletions
diff --git a/tvix/nar-bridge/pkg/reader/reader.go b/tvix/nar-bridge/pkg/reader/reader.go
index 6d34cd168d..9ff7b3fedb 100644
--- a/tvix/nar-bridge/pkg/reader/reader.go
+++ b/tvix/nar-bridge/pkg/reader/reader.go
@@ -190,15 +190,21 @@ func (r *Reader) Import(
 			// Check for valid path transitions, pop from stack if needed
 			// The nar reader already gives us some guarantees about ordering and illegal transitions,
 			// So we really only need to check if the top-of-stack path is a prefix of the path,
-			// and if it's not, pop from the stack.
+			// and if it's not, pop from the stack. We do this repeatedly until the top of the stack is
+			// the subdirectory the new entry is in, or we hit the root directory.
 
 			// We don't need to worry about the root node case, because we can only finish the root "/"
 			// If we're at the end of the NAR reader (covered by the EOF check)
-			if len(stack) > 0 && !strings.HasPrefix(hdr.Path, stack[len(stack)-1].path) {
-				err := popFromStack()
-				if err != nil {
-					return nil, fmt.Errorf("unable to pop from stack: %w", err)
+			for {
+				// We never want to pop the root directory until we're completely done.
+				if len(stack) > 1 && !strings.HasPrefix(hdr.Path, stack[len(stack)-1].path+"/") {
+					err := popFromStack()
+					if err != nil {
+						return nil, fmt.Errorf("unable to pop from stack: %w", err)
+					}
+					continue
 				}
+				break
 			}
 
 			if hdr.Type == nar.TypeSymlink {
diff --git a/tvix/nar-bridge/pkg/reader/reader_test.go b/tvix/nar-bridge/pkg/reader/reader_test.go
index 6ca1ca2d74..1ba9c9651c 100644
--- a/tvix/nar-bridge/pkg/reader/reader_test.go
+++ b/tvix/nar-bridge/pkg/reader/reader_test.go
@@ -566,3 +566,31 @@ func TestCallbackErrors(t *testing.T) {
 		require.ErrorIs(t, err, targetErr)
 	})
 }
+
+// TestPopDirectories is a regression test that ensures we handle the directory
+// stack properly.
+//
+// This test case looks like:
+//
+// / (dir)
+// /test (dir)
+// /test/tested (file)
+// /tested (file)
+//
+// We used to have a bug where the second `tested` file would appear as if
+// it was in the `/test` dir because it has that dir as a string prefix.
+func TestPopDirectories(t *testing.T) {
+	f, err := os.Open("../../testdata/popdirectories.nar")
+	require.NoError(t, err)
+	defer f.Close()
+
+	r := reader.New(f)
+	_, err = r.Import(
+		context.Background(),
+		func(fileReader io.Reader) error { return nil },
+		func(directory *storev1pb.Directory) error {
+			return directory.Validate()
+		},
+	)
+	require.NoError(t, err)
+}
diff --git a/tvix/nar-bridge/testdata/popdirectories.nar b/tvix/nar-bridge/testdata/popdirectories.nar
new file mode 100644
index 0000000000..74313aca52
--- /dev/null
+++ b/tvix/nar-bridge/testdata/popdirectories.nar
Binary files differ