windows: ignore file attributes

On Windows a FILE_ACTION_MODIFIED event (i.e. a Write event) is
triggered on file attribute changes, rather than some dedicates
ATTRIBUTE_CHANGED event. Looking at the docs, I don't really see a way
to distinguish between "real" write events and attribute changes. This is
very odd, but seems to be how the ReadDirectoryChangesW() API works.

The only way I can see to distinguish between the two events is to set
up two filters: one with a FILE_NOTIFY_CHANGE_ATTRIBUTES, and one
without. But that seems overly complex, and no one asked to get Chmod
events for Windows; it's not really all that interesting on Windows
anyway.

The problem is that some software (anti-virus, backup software, etc.)
can issue lots of attribute changes, causing a lot of "fake" Write
events.

So remove the FILE_NOTIFY_CHANGE_ATTRIBUTES and sysFSATTRIB flags.

This was adapted from some changes done in the tilt-dev/fsnotify fork;
specifically:
f6dca35
3ee2a2f

Fixes #487

backend_windows.go

@@ -294,7 +294,6 @@ func (w *Watcher) WatchList() []string {
 // This should all be removed at some point, and just use windows.FILE_NOTIFY_*
 const (
 	sysFSALLEVENTS  = 0xfff
-	sysFSATTRIB     = 0x4
 	sysFSCREATE     = 0x100
 	sysFSDELETE     = 0x200
 	sysFSDELETESELF = 0x400
@@ -320,9 +319,6 @@ func (w *Watcher) newEvent(name string, mask uint32) Event {
 	if mask&sysFSMOVE == sysFSMOVE || mask&sysFSMOVESELF == sysFSMOVESELF || mask&sysFSMOVEDFROM == sysFSMOVEDFROM {
 		e.Op |= Rename
 	}
-	if mask&sysFSATTRIB == sysFSATTRIB {
-		e.Op |= Chmod
-	}
 	return e
 }
 
@@ -735,9 +731,6 @@ func (w *Watcher) toWindowsFlags(mask uint64) uint32 {
 	if mask&sysFSMODIFY != 0 {
 		m |= windows.FILE_NOTIFY_CHANGE_LAST_WRITE
 	}
-	if mask&sysFSATTRIB != 0 {
-		m |= windows.FILE_NOTIFY_CHANGE_ATTRIBUTES
-	}
 	if mask&(sysFSMOVE|sysFSCREATE|sysFSDELETE) != 0 {
 		m |= windows.FILE_NOTIFY_CHANGE_FILE_NAME | windows.FILE_NOTIFY_CHANGE_DIR_NAME
 	}

backend_windows_test.go

@@ -50,3 +50,18 @@ func TestRemoveState(t *testing.T) {
 	}
 	check(0)
 }
+
+func TestWindowsNoAttributeChanges(t *testing.T) {
+	tmp := t.TempDir()
+	file := filepath.Join(tmp, "TestFsnotifyEventsExisting.testfile")
+
+	touch(t, file) // Create a file before watching directory
+	w := newCollector(t, tmp)
+	w.collect(t)
+	chmod(t, 0o400, file) // Make the file read-only, which is an attribute change
+
+	have := w.stop(t)
+	if len(have) != 0 {
+		t.Fatalf("should not have received any events, received:\n%s", have)
+	}
+}

fsnotify_test.go

@@ -252,20 +252,12 @@ func TestWatchCreate(t *testing.T) {
 			symlink(t, filepath.Join(tmp, "file"), tmp, "link")
 		}, `
 			create  /link
-
-			windows:
-				create   /link
-				write    /link
 		`},
 		{"create new symlink to directory", func(t *testing.T, w *Watcher, tmp string) {
 			addWatch(t, w, tmp)
 			symlink(t, tmp, tmp, "link")
 		}, `
 			create  /link
-
-			windows:
-				create  /link
-				write  /link
 		`},
 
 		// FIFO
@@ -548,10 +540,6 @@ func TestWatchSymlink(t *testing.T) {
 		}, `
 			create /link
 
-			windows:
-				create    /link
-				write     /link
-
 			# No events at all on Dragonfly
 			# TODO: should fix this.
 			dragonfly: