shows implementation impact of UnimplementedFile (#1424)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/platform/file_test.go

@@ -0,0 +1,21 @@
+package platform
+
+import (
+	"io/fs"
+	"syscall"
+)
+
+var _ File = NoopFile{}
+
+// NoopFile shows the minimal methods a type embedding UnimplementedFile must
+// implement.
+type NoopFile struct {
+	UnimplementedFile
+}
+
+// The current design requires the user to consciously implement Close.
+// However, we could change UnimplementedFile to return zero.
+func (n NoopFile) Close() (errno syscall.Errno) { return }
+
+// Once File.File is removed, it will be possible to implement NoopFile.
+func (n NoopFile) File() fs.File { panic("noop") }