hugolib: Init the content and shortcodes early

In most cases we could delay the content init until rendering time, but there could be use cases where the templates would depend on state set in the shortcodes (.Page.Scratch.Set), so we  need to do this early.

See #4632

hugolib/hugo_sites.go

@@ -560,22 +560,40 @@ func (h *HugoSites) setupTranslations() {
 }
 
 func (s *Site) preparePagesForRender(cfg *BuildCfg) {
+
+	pageChan := make(chan *Page)
+	wg := &sync.WaitGroup{}
+
+	numWorkers := getGoMaxProcs() * 4
+
+	for i := 0; i < numWorkers; i++ {
+		wg.Add(1)
+		go func(pages <-chan *Page, wg *sync.WaitGroup) {
+			defer wg.Done()
+			for p := range pages {
+				p.setContentInit(cfg)
+
+				// In most cases we could delay the content init until rendering time,
+				// but there could be use cases where the templates would depend
+				// on state set in the shortcodes (.Page.Scratch.Set), so we
+				// need to do this early. This will do the needed recursion.
+				p.initContent()
+			}
+		}(pageChan, wg)
+	}
+
 	for _, p := range s.Pages {
-		p.setContentInit(cfg)
-		// The skip render flag is used in many tests. To make sure that they
-		// have access to the content, we need to manually initialize it here.
-		if cfg.SkipRender {
-			p.initContent()
-		}
+		pageChan <- p
 	}
 
 	for _, p := range s.headlessPages {
-		p.setContentInit(cfg)
-		if cfg.SkipRender {
-			p.initContent()
-		}
+		pageChan <- p
 	}
 
+	close(pageChan)
+
+	wg.Wait()
+
 }
 
 // Pages returns all pages for all sites.