1 files changed, 88 insertions, 0 deletions
diff --git a/internal/robustio/robustio_test.go b/internal/robustio/robustio_test.go
new file mode 100644
index 000000000..10244e21d
--- /dev/null
+++ b/internal/robustio/robustio_test.go
@@ -0,0 +1,88 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package robustio_test
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+	"time"
+
+	"golang.org/x/tools/internal/robustio"
+)
+
+func TestFileInfo(t *testing.T) {
+	// A nonexistent file has no ID.
+	nonexistent := filepath.Join(t.TempDir(), "nonexistent")
+	if _, _, err := robustio.GetFileID(nonexistent); err == nil {
+		t.Fatalf("GetFileID(nonexistent) succeeded unexpectedly")
+	}
+
+	// A regular file has an ID.
+	real := filepath.Join(t.TempDir(), "real")
+	if err := os.WriteFile(real, nil, 0644); err != nil {
+		t.Fatalf("can't create regular file: %v", err)
+	}
+	realID, realMtime, err := robustio.GetFileID(real)
+	if err != nil {
+		t.Fatalf("can't get ID of regular file: %v", err)
+	}
+
+	// Sleep so that we get a new mtime for subsequent writes.
+	time.Sleep(2 * time.Second)
+
+	// A second regular file has a different ID.
+	real2 := filepath.Join(t.TempDir(), "real2")
+	if err := os.WriteFile(real2, nil, 0644); err != nil {
+		t.Fatalf("can't create second regular file: %v", err)
+	}
+	real2ID, real2Mtime, err := robustio.GetFileID(real2)
+	if err != nil {
+		t.Fatalf("can't get ID of second regular file: %v", err)
+	}
+	if realID == real2ID {
+		t.Errorf("realID %+v == real2ID %+v", realID, real2ID)
+	}
+	if realMtime.Equal(real2Mtime) {
+		t.Errorf("realMtime %v == real2Mtime %v", realMtime, real2Mtime)
+	}
+
+	// A symbolic link has the same ID as its target.
+	if runtime.GOOS != "plan9" {
+		symlink := filepath.Join(t.TempDir(), "symlink")
+		if err := os.Symlink(real, symlink); err != nil {
+			t.Fatalf("can't create symbolic link: %v", err)
+		}
+		symlinkID, symlinkMtime, err := robustio.GetFileID(symlink)
+		if err != nil {
+			t.Fatalf("can't get ID of symbolic link: %v", err)
+		}
+		if realID != symlinkID {
+			t.Errorf("realID %+v != symlinkID %+v", realID, symlinkID)
+		}
+		if !realMtime.Equal(symlinkMtime) {
+			t.Errorf("realMtime %v != symlinkMtime %v", realMtime, symlinkMtime)
+		}
+	}
+
+	// Two hard-linked files have the same ID.
+	if runtime.GOOS != "plan9" && runtime.GOOS != "android" {
+		hardlink := filepath.Join(t.TempDir(), "hardlink")
+		if err := os.Link(real, hardlink); err != nil {
+			t.Fatal(err)
+		}
+		hardlinkID, hardlinkMtime, err := robustio.GetFileID(hardlink)
+		if err != nil {
+			t.Fatalf("can't get ID of hard link: %v", err)
+		}
+		if realID != hardlinkID {
+			t.Errorf("realID %+v != hardlinkID %+v", realID, hardlinkID)
+		}
+		if !realMtime.Equal(hardlinkMtime) {
+			t.Errorf("realMtime %v != hardlinkMtime %v", realMtime, hardlinkMtime)
+		}
+	}
+}