From 09a408664d22556ea8b807cc06ceafa63d869e72 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Fri, 12 May 2023 11:42:22 +0100
Subject: [PATCH] fs: create Overlay feature flag to indicate backend wraps
 others

Set this automatically for any backend which implements UnWrap and
manually for combine and union which can't implement UnWrap but do
overlay other backends.
---
 backend/combine/combine.go | 3 +++
 backend/union/union.go     | 3 +++
 fs/features.go             | 5 +++++
 fstest/fstests/fstests.go  | 2 +-
 4 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/backend/combine/combine.go b/backend/combine/combine.go
index 2e1ad2a7b..2457bc4f1 100644
--- a/backend/combine/combine.go
+++ b/backend/combine/combine.go
@@ -299,6 +299,9 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (outFs fs
 		}
 	}
 
+	// show that we wrap other backends
+	features.Overlay = true
+
 	f.features = features
 
 	// Get common intersection of hashes
diff --git a/backend/union/union.go b/backend/union/union.go
index 1b3c0f4db..78a713896 100644
--- a/backend/union/union.go
+++ b/backend/union/union.go
@@ -914,6 +914,9 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		}
 	}
 
+	// show that we wrap other backends
+	features.Overlay = true
+
 	f.features = features
 
 	// Get common intersection of hashes
diff --git a/fs/features.go b/fs/features.go
index 2ba54abe2..4c3612285 100644
--- a/fs/features.go
+++ b/fs/features.go
@@ -32,6 +32,7 @@ type Features struct {
 	FilterAware             bool // can make use of filters if provided for listing
 	PartialUploads          bool // uploaded file can appear incomplete on the fs while it's being uploaded
 	NoMultiThreading        bool // set if can't have multiplethreads on one download open
+	Overlay                 bool // this wraps one or more backends to add functionality
 
 	// Purge all files in the directory specified
 	//
@@ -271,6 +272,7 @@ func (ft *Features) Fill(ctx context.Context, f Fs) *Features {
 	if do, ok := f.(Wrapper); ok {
 		ft.WrapFs = do.WrapFs
 		ft.SetWrapper = do.SetWrapper
+		ft.Overlay = true // if implement UnWrap then must be an Overlay
 	}
 	if do, ok := f.(DirCacheFlusher); ok {
 		ft.DirCacheFlush = do.DirCacheFlush
@@ -339,6 +341,9 @@ func (ft *Features) Mask(ctx context.Context, f Fs) *Features {
 	ft.SlowModTime = ft.SlowModTime && mask.SlowModTime
 	ft.SlowHash = ft.SlowHash && mask.SlowHash
 	ft.FilterAware = ft.FilterAware && mask.FilterAware
+	ft.PartialUploads = ft.PartialUploads && mask.PartialUploads
+	ft.NoMultiThreading = ft.NoMultiThreading && mask.NoMultiThreading
+	// ft.Overlay = ft.Overlay && mask.Overlay don't propagate Overlay
 
 	if mask.Purge == nil {
 		ft.Purge = nil
diff --git a/fstest/fstests/fstests.go b/fstest/fstests/fstests.go
index 46a6ff4b5..ddd20c97a 100644
--- a/fstest/fstests/fstests.go
+++ b/fstest/fstests/fstests.go
@@ -460,7 +460,7 @@ func Run(t *testing.T, opt *Opt) {
 			t.Skip("Skipping FsCheckWrap on this Fs")
 		}
 		ft := new(fs.Features).Fill(ctx, f)
-		if ft.UnWrap == nil {
+		if ft.UnWrap == nil && !f.Features().Overlay {
 			t.Skip("Not a wrapping Fs")
 		}
 		v := reflect.ValueOf(ft).Elem()