4 files changed, 76 insertions, 8 deletions
diff --git a/internal/scan/fileid_other.go b/internal/scan/fileid_other.go
new file mode 100644
index 0000000..503a9b4
--- /dev/null
+++ b/internal/scan/fileid_other.go
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build !unix
+
+package scan
+
+import "io/fs"
+
+// fileID reports no identity where the platform has no inodes.
+func fileID(fs.FileInfo) (dev, ino uint64) { return 0, 0 }
diff --git a/internal/scan/fileid_unix.go b/internal/scan/fileid_unix.go
new file mode 100644
index 0000000..e29066a
--- /dev/null
+++ b/internal/scan/fileid_unix.go
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build unix
+
+package scan
+
+import (
+	"io/fs"
+	"syscall"
+)
+
+// fileID returns the device and inode info was read from.
+func fileID(info fs.FileInfo) (dev, ino uint64) {
+	st, ok := info.Sys().(*syscall.Stat_t)
+	if !ok {
+		return 0, 0
+	}
+	return uint64(st.Dev), uint64(st.Ino)
+}
diff --git a/internal/scan/scan.go b/internal/scan/scan.go
index 7fe9e92..77cca66 100644
--- a/internal/scan/scan.go
+++ b/internal/scan/scan.go
@@ -24,6 +24,26 @@ type File struct {
 	Size    int64
 	ModTime time.Time
 	Mode    fs.FileMode
+
+	// Dev and Ino identify the file on its filesystem; both are 0 where the
+	// platform reports neither.
+	Dev, Ino uint64
+}
+
+// NewFile builds the File for path, at rel under the root, from its Lstat
+// info.
+func NewFile(path, rel string, info fs.FileInfo) File {
+	dev, ino := fileID(info)
+	return File{
+		Path:    path,
+		Rel:     rel,
+		Name:    filepath.Base(path),
+		Size:    info.Size(),
+		ModTime: info.ModTime(),
+		Mode:    info.Mode(),
+		Dev:     dev,
+		Ino:     ino,
+	}
 }
 
 // Reason is why an entry was not returned as a File.
@@ -217,14 +237,7 @@ func (w *walker) walk(dir, relDir string, depth int, entries []os.DirEntry) erro
 			w.result.Skipped = append(w.result.Skipped, Skipped{Rel: rel, Reason: TooBig})
 			continue
 		}
-		w.result.Files = append(w.result.Files, File{
-			Path:    path,
-			Rel:     rel,
-			Name:    name,
-			Size:    info.Size(),
-			ModTime: info.ModTime(),
-			Mode:    info.Mode(),
-		})
+		w.result.Files = append(w.result.Files, NewFile(path, rel, info))
 	}
 	return nil
 }
diff --git a/internal/scan/scan_test.go b/internal/scan/scan_test.go
index a245893..e9aeb73 100644
--- a/internal/scan/scan_test.go
+++ b/internal/scan/scan_test.go
@@ -293,3 +293,29 @@ func TestTooBig(t *testing.T) {
 		t.Errorf("MaxSize 0 skipped files: %v", skipped(r))
 	}
 }
+
+// TestFilesCarryInode: a walked file carries its device and inode, which a
+// rename keeps.
+func TestFilesCarryInode(t *testing.T) {
+	root := tree(t)
+	p := filepath.Join(root, "a.txt")
+	if err := os.WriteFile(p, []byte("x"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	old := now.Add(-time.Hour)
+	os.Chtimes(p, old, old)
+	first, err := Walk(root, Options{Now: now})
+	if err != nil || len(first.Files) != 1 {
+		t.Fatalf("walk: %v %+v", err, first)
+	}
+	if first.Files[0].Ino == 0 {
+		t.Fatal("no inode on a unix filesystem")
+	}
+	if err := os.Rename(p, filepath.Join(root, "b.txt")); err != nil {
+		t.Fatal(err)
+	}
+	second, _ := Walk(root, Options{Now: now})
+	if len(second.Files) != 1 || second.Files[0].Ino != first.Files[0].Ino || second.Files[0].Dev != first.Files[0].Dev {
+		t.Errorf("rename changed the identity: %+v then %+v", first.Files[0], second.Files)
+	}
+}