lib/model, lib/scanner: Properly ignore symlinks on Windows (fixes #4035)

Adds a unit test to ensure we don't scan symlinks on Windows. For the
rwfolder, trusts that the logic in the invalid check is correct and that
the check is actually called from the need loop.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4042

lib/scanner/walk_test.go

@@ -280,7 +280,7 @@ func TestIssue1507(t *testing.T) {
 	fn("", nil, protocol.ErrClosed)
 }
 
-func TestWalkSymlink(t *testing.T) {
+func TestWalkSymlinkUnix(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("skipping unsupported symlink test")
 		return
@@ -323,6 +323,45 @@ func TestWalkSymlink(t *testing.T) {
 	}
 }
 
+func TestWalkSymlinkWindows(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skip("skipping unsupported symlink test")
+	}
+
+	// Create a folder with a symlink in it
+
+	os.RemoveAll("_symlinks")
+	defer os.RemoveAll("_symlinks")
+
+	os.Mkdir("_symlinks", 0755)
+	if err := os.Symlink("destination", "_symlinks/link"); err != nil {
+		// Probably we require permissions we don't have.
+		t.Skip(err)
+	}
+
+	// Scan it
+
+	fchan, err := Walk(Config{
+		Dir:       "_symlinks",
+		BlockSize: 128 * 1024,
+	})
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var files []protocol.FileInfo
+	for f := range fchan {
+		files = append(files, f)
+	}
+
+	// Verify that we got zero symlinks
+
+	if len(files) != 0 {
+		t.Errorf("expected zero symlinks, not %d", len(files))
+	}
+}
+
 func walkDir(dir string) ([]protocol.FileInfo, error) {
 	fchan, err := Walk(Config{
 		Dir:           dir,