hugolib: Force render of any changed page, even in Fast Render Mode

Fixes gohugoio#5083

hugolib/hugo_sites.go

@@ -366,6 +366,11 @@ type BuildCfg struct {
 // Note that a page does not have to have a content page / file.
 // For regular builds, this will allways return true.
 func (cfg *BuildCfg) shouldRender(p *Page) bool {
+	if p.forceRender {
+		p.forceRender = false
+		return true
+	}
+
 	if len(cfg.RecentlyVisited) == 0 {
 		return true
 	}

hugolib/page.go

@@ -265,6 +265,11 @@ type Page struct {
 
 	lang string
 
+	// When in Fast Render Mode, we only render a sub set of the pages, i.e. the
+	// pages the user is working on. There are, however, situations where we need to
+	// signal other pages to be rendered.
+	forceRender bool
+
 	// The output formats this page will be rendered to.
 	outputFormats output.Formats
 

hugolib/page_bundler.go

@@ -110,6 +110,7 @@ func (s *siteContentProcessor) process(ctx context.Context) error {
 			}
 
 			if s.partialBuild {
+				p.forceRender = true
 				s.site.replacePage(p)
 			} else {
 				s.site.addPage(p)