lib/ignore, lib/model: Use an interface to detect file changes, improving tests

This solves the erratic test failures on model.TestIgnores by ensuring
that the ignore patterns are reloaded even in the face of unchanged
timestamps.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4208

lib/model/model_test.go

@@ -953,14 +953,6 @@ func changeIgnores(t *testing.T, m *Model, expected []string) {
 
 	ignores = append(ignores, "pox")
 
-	if runtime.GOOS == "darwin" {
-		// Mac has seconds-only timestamp precision, which tricks the ignore
-		// system into thinking the file has not changed. Work around it in
-		// an ugly way...
-		time.Sleep(time.Second)
-	} else {
-		time.Sleep(time.Millisecond)
-	}
 	err = m.SetIgnores("default", ignores)
 	if err != nil {
 		t.Error(err)
@@ -1011,6 +1003,14 @@ func TestIgnores(t *testing.T) {
 	m.AddFolder(defaultFolderConfig)
 	m.StartFolder("default")
 
+	// Reach in and update the ignore matcher to one that always does
+	// reloads when asked to, instead of checking file mtimes. This is
+	// because we will be changing the files on disk often enough that the
+	// mtimes will be unreliable to determine change status.
+	m.fmut.Lock()
+	m.folderIgnores["default"] = ignore.New(ignore.WithCache(true), ignore.WithChangeDetector(newAlwaysChanged()))
+	m.fmut.Unlock()
+
 	// Make sure the initial scan has finished (ScanFolders is blocking)
 	m.ScanFolders()
 
@@ -1843,7 +1843,7 @@ func TestIssue3164(t *testing.T) {
 	f := protocol.FileInfo{
 		Name: "issue3164",
 	}
-	m := ignore.New(false)
+	m := ignore.New()
 	if err := m.Parse(bytes.NewBufferString("(?d)oktodelete"), ""); err != nil {
 		t.Fatal(err)
 	}
@@ -2490,3 +2490,31 @@ func (fakeAddr) Network() string {
 func (fakeAddr) String() string {
 	return "address"
 }
+
+// alwaysChanges is an ignore.ChangeDetector that always returns true on Changed()
+type alwaysChanged struct {
+	seen map[string]struct{}
+}
+
+func newAlwaysChanged() *alwaysChanged {
+	return &alwaysChanged{
+		seen: make(map[string]struct{}),
+	}
+}
+
+func (c *alwaysChanged) Remember(name string, _ time.Time) {
+	c.seen[name] = struct{}{}
+}
+
+func (c *alwaysChanged) Reset() {
+	c.seen = make(map[string]struct{})
+}
+
+func (c *alwaysChanged) Seen(name string) bool {
+	_, ok := c.seen[name]
+	return ok
+}
+
+func (c *alwaysChanged) Changed() bool {
+	return true
+}