Simplify page tree logic

This is preparation for #6041.

For historic reasons, the code for bulding the section tree and the taxonomies were very much separate.

This works, but makes it hard to extend, maintain, and possibly not so fast as it could be.

This simplification also introduces 3 slightly breaking changes, which I suspect most people will be pleased about. See referenced issues:

This commit also switches the radix tree dependency to a mutable implementation: github.com/armon/go-radix.

Fixes #6154
Fixes #6153
Fixes #6152

hugolib/hugo_sites_build.go

@@ -18,7 +18,6 @@ import (
 	"context"
 	"fmt"
 	"runtime/trace"
-	"sort"
 
 	"github.com/gohugoio/hugo/output"
 
@@ -31,6 +30,7 @@ import (
 // Build builds all sites. If filesystem events are provided,
 // this is considered to be a potential partial rebuild.
 func (h *HugoSites) Build(config BuildCfg, events ...fsnotify.Event) error {
+
 	if h.running {
 		// Make sure we don't trigger rebuilds in parallel.
 		h.runningMu.Lock()
@@ -75,25 +75,29 @@ func (h *HugoSites) Build(config BuildCfg, events ...fsnotify.Event) error {
 
 	if !config.PartialReRender {
 		prepare := func() error {
-			for _, s := range h.Sites {
-				s.Deps.BuildStartListeners.Notify()
-			}
+			init := func(conf *BuildCfg) error {
+				for _, s := range h.Sites {
+					s.Deps.BuildStartListeners.Notify()
+				}
 
-			if len(events) > 0 {
-				// Rebuild
-				if err := h.initRebuild(conf); err != nil {
-					return errors.Wrap(err, "initRebuild")
-				}
-			} else {
-				if err := h.initSites(conf); err != nil {
-					return errors.Wrap(err, "initSites")
+				if len(events) > 0 {
+					// Rebuild
+					if err := h.initRebuild(conf); err != nil {
+						return errors.Wrap(err, "initRebuild")
+					}
+				} else {
+					if err := h.initSites(conf); err != nil {
+						return errors.Wrap(err, "initSites")
+					}
 				}
+
+				return nil
 			}
 
 			var err error
 
 			f := func() {
-				err = h.process(conf, events...)
+				err = h.process(conf, init, events...)
 			}
 			trace.WithRegion(ctx, "process", f)
 			if err != nil {
@@ -195,7 +199,7 @@ func (h *HugoSites) initRebuild(config *BuildCfg) error {
 	}
 
 	for _, s := range h.Sites {
-		s.resetBuildState()
+		s.resetBuildState(config.whatChanged.source)
 	}
 
 	h.reset(config)
@@ -205,7 +209,7 @@ func (h *HugoSites) initRebuild(config *BuildCfg) error {
 	return nil
 }
 
-func (h *HugoSites) process(config *BuildCfg, events ...fsnotify.Event) error {
+func (h *HugoSites) process(config *BuildCfg, init func(config *BuildCfg) error, events ...fsnotify.Event) error {
 	// We should probably refactor the Site and pull up most of the logic from there to here,
 	// but that seems like a daunting task.
 	// So for now, if there are more than one site (language),
@@ -215,9 +219,7 @@ func (h *HugoSites) process(config *BuildCfg, events ...fsnotify.Event) error {
 
 	if len(events) > 0 {
 		// This is a rebuild
-		changed, err := firstSite.processPartial(events)
-		config.whatChanged = &changed
-		return err
+		return firstSite.processPartial(config, init, events)
 	}
 
 	return firstSite.process(*config)
@@ -235,26 +237,27 @@ func (h *HugoSites) assemble(config *BuildCfg) error {
 		}
 	}
 
-	if err := h.createPageCollections(); err != nil {
-		return err
-	}
-
-	if config.whatChanged.source {
-		for _, s := range h.Sites {
-			if err := s.assembleTaxonomies(); err != nil {
-				return err
-			}
-		}
-	}
-
-	// Create pagexs for the section pages etc. without content file.
-	if err := h.createMissingPages(); err != nil {
-		return err
+	if !config.whatChanged.source {
+		return nil
 	}
 
 	for _, s := range h.Sites {
-		s.setupSitePages()
-		sort.Stable(s.workAllPages)
+		if err := s.assemblePagesMap(s); err != nil {
+			return err
+		}
+
+		if err := s.pagesMap.assembleTaxonomies(s); err != nil {
+			return err
+		}
+
+		if err := s.createWorkAllPages(); err != nil {
+			return err
+		}
+
+	}
+
+	if err := h.createPageCollections(); err != nil {
+		return err
 	}
 
 	return nil