hugolib: Ignore non-source files on partial rebuild

Partial rebuild does not have the same logic as normal rebuild on
selecting which file to build. This change makes it possible to
share the file select logic between two kinds of build.

Fix #3325.

hugolib/site.go

@@ -728,6 +728,9 @@ func (s *Site) reProcess(events []fsnotify.Event) (whatChanged, error) {
 		go pageConverter(pageChan, convertResults, wg2)
 	}
 
+	sp := source.NewSourceSpec(s.Cfg, s.Fs)
+	fs := sp.NewFilesystem("")
+
 	for _, ev := range sourceChanged {
 		// The incrementalReadCollator below will also make changes to the site's pages,
 		// so we do this first to prevent races.
@@ -750,6 +753,15 @@ func (s *Site) reProcess(events []fsnotify.Event) (whatChanged, error) {
 			}
 		}
 
+		// ignore files shouldn't be proceed
+		if fi, err := s.Fs.Source.Stat(ev.Name); err != nil {
+			continue
+		} else {
+			if ok, err := fs.ShouldRead(ev.Name, fi); err != nil || !ok {
+				continue
+			}
+		}
+
 		sourceReallyChanged = append(sourceReallyChanged, ev)
 	}