Prevent stale content in Fast Render Mode

We do that by re-render visited pages that is not already in the stack. This may potentially do some double work, but that small penalty should be well worth it.

Fixes #5281

3 files changed, 33 insertions, 13 deletions

diff --git a/commands/commandeer.go b/commands/commandeer.go
index 2b76462fe..94b2c6553 100644
--- a/commands/commandeer.go
+++ b/commands/commandeer.go
@@ -324,10 +324,7 @@ func (c *commandeer) loadConfig(mustHaveConfigFile, running bool) error {
 			fs.Destination = new(afero.MemMapFs)
 		}
 
-		doLiveReload := !c.h.buildWatch && !config.GetBool("disableLiveReload")
-		fastRenderMode := doLiveReload && !config.GetBool("disableFastRender")
-
-		if fastRenderMode {
+		if c.fastRenderMode {
 			// For now, fast render mode only. It should, however, be fast enough
 			// for the full variant, too.
 			changeDetector := &fileChangeDetector{
diff --git a/commands/hugo.go b/commands/hugo.go
index 6cb2ec012..deaa1f7ff 100644
--- a/commands/hugo.go
+++ b/commands/hugo.go
@@ -618,13 +618,20 @@ func (c *commandeer) buildSites() (err error) {
 	return c.hugo.Build(hugolib.BuildCfg{})
 }
 
+func (c *commandeer) handleBuildErr(err error, msg string) {
+	c.buildErr = err
+	c.logger.ERROR.Printf("%s: %s", msg, err)
+	if !c.h.quiet && c.h.verbose {
+		herrors.PrintStackTrace(err)
+	}
+}
+
 func (c *commandeer) rebuildSites(events []fsnotify.Event) error {
 	defer c.timeTrack(time.Now(), "Total")
 
 	c.buildErr = nil
 	visited := c.visitedURLs.PeekAllSet()
-	doLiveReload := !c.h.buildWatch && !c.Cfg.GetBool("disableLiveReload")
-	if doLiveReload && !c.Cfg.GetBool("disableFastRender") {
+	if c.fastRenderMode {
 
 		// Make sure we always render the home pages
 		for _, l := range c.languages {
@@ -640,6 +647,15 @@ func (c *commandeer) rebuildSites(events []fsnotify.Event) error {
 	return c.hugo.Build(hugolib.BuildCfg{RecentlyVisited: visited}, events...)
 }
 
+func (c *commandeer) partialReRender(urls ...string) error {
+	c.buildErr = nil
+	visited := make(map[string]bool)
+	for _, url := range urls {
+		visited[url] = true
+	}
+	return c.hugo.Build(hugolib.BuildCfg{RecentlyVisited: visited, PartialReRender: true})
+}
+
 func (c *commandeer) fullRebuild() {
 	c.commandeerHugoState = &commandeerHugoState{}
 	err := c.loadConfig(true, true)
@@ -907,15 +923,10 @@ func (c *commandeer) handleEvents(watcher *watcher.Batcher,
 
 		c.changeDetector.PrepareNew()
 		if err := c.rebuildSites(dynamicEvents); err != nil {
-			c.buildErr = err
-			c.logger.ERROR.Printf("Rebuild failed: %s", err)
-			if !c.h.quiet && c.h.verbose {
-				herrors.PrintStackTrace(err)
-			}
+			c.handleBuildErr(err, "Rebuild failed")
 		}
 
 		if doLiveReload {
-
 			if len(partitionedEvents.ContentEvents) == 0 && len(partitionedEvents.AssetEvents) > 0 {
 				changed := c.changeDetector.changed()
 				if c.changeDetector != nil && len(changed) == 0 {
diff --git a/commands/server.go b/commands/server.go
index ffdbc95c9..7b7164eea 100644
--- a/commands/server.go
+++ b/commands/server.go
@@ -345,10 +345,22 @@ func (f *fileServer) createEndpoint(i int) (*http.ServeMux, string, string, erro
 				w.Header().Set("Pragma", "no-cache")
 			}
 
-			if f.c.fastRenderMode {
+			if f.c.fastRenderMode && f.c.buildErr == nil {
 				p := r.RequestURI
 				if strings.HasSuffix(p, "/") || strings.HasSuffix(p, "html") || strings.HasSuffix(p, "htm") {
+					if !f.c.visitedURLs.Contains(p) {
+						// If not already on stack, re-render that single page.
+						if err := f.c.partialReRender(p); err != nil {
+							f.c.handleBuildErr(err, fmt.Sprintf("Failed to render %q", p))
+							if f.c.showErrorInBrowser {
+								http.Redirect(w, r, p, 301)
+								return
+							}
+						}
+					}
+
 					f.c.visitedURLs.Add(p)
+
 				}
 			}
 			h.ServeHTTP(w, r)