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/page.go

@@ -23,6 +23,8 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/maps"
+
 	"github.com/gohugoio/hugo/hugofs/files"
 
 	"github.com/bep/gitmap"
@@ -121,31 +123,66 @@ func (p *pageState) MarshalJSON() ([]byte, error) {
 	return page.MarshalPageToJSON(p)
 }
 
-func (p *pageState) Pages() page.Pages {
-	p.pagesInit.Do(func() {
-		if p.pages != nil {
-			return
-		}
+func (p *pageState) getPages() page.Pages {
+	b := p.bucket
+	if b == nil {
+		return nil
+	}
+	return b.getPages()
+}
 
+func (p *pageState) getPagesAndSections() page.Pages {
+	b := p.bucket
+	if b == nil {
+		return nil
+	}
+	return b.getPagesAndSections()
+}
+
+// TODO(bep) cm add a test
+func (p *pageState) RegularPages() page.Pages {
+	p.regularPagesInit.Do(func() {
 		var pages page.Pages
 
 		switch p.Kind() {
 		case page.KindPage:
-		case page.KindHome:
-			pages = p.s.RegularPages()
+		case page.KindSection, page.KindHome, page.KindTaxonomyTerm:
+			pages = p.getPages()
 		case page.KindTaxonomy:
-			termInfo := p.getTaxonomyNodeInfo()
-			taxonomy := p.s.Taxonomies[termInfo.plural].Get(termInfo.termKey)
-			pages = taxonomy.Pages()
-		case page.KindTaxonomyTerm:
-			plural := p.getTaxonomyNodeInfo().plural
-			// A list of all page.KindTaxonomy pages with matching plural
-			for _, p := range p.s.findPagesByKind(page.KindTaxonomy) {
-				if p.SectionsEntries()[0] == plural {
+			all := p.Pages()
+			for _, p := range all {
+				if p.IsPage() {
 					pages = append(pages, p)
 				}
 			}
-		case kind404, kindSitemap, kindRobotsTXT:
+		default:
+			pages = p.s.RegularPages()
+		}
+
+		p.regularPages = pages
+
+	})
+
+	return p.regularPages
+}
+
+func (p *pageState) Pages() page.Pages {
+	p.pagesInit.Do(func() {
+		var pages page.Pages
+
+		switch p.Kind() {
+		case page.KindPage:
+		case page.KindSection, page.KindHome:
+			pages = p.getPagesAndSections()
+		case page.KindTaxonomy:
+			termInfo := p.bucket
+			plural := maps.GetString(termInfo.meta, "plural")
+			term := maps.GetString(termInfo.meta, "termKey")
+			taxonomy := p.s.Taxonomies[plural].Get(term)
+			pages = taxonomy.Pages()
+		case page.KindTaxonomyTerm:
+			pages = p.getPagesAndSections()
+		default:
 			pages = p.s.Pages()
 		}
 
@@ -295,10 +332,9 @@ func (p *pageState) getLayoutDescriptor() output.LayoutDescriptor {
 			if len(sections) > 0 {
 				section = sections[0]
 			}
-		case page.KindTaxonomyTerm:
-			section = p.getTaxonomyNodeInfo().singular
-		case page.KindTaxonomy:
-			section = p.getTaxonomyNodeInfo().parent.singular
+		case page.KindTaxonomyTerm, page.KindTaxonomy:
+			section = maps.GetString(p.bucket.meta, "singular")
+
 		default:
 		}
 
@@ -359,11 +395,6 @@ func (p *pageState) initPage() error {
 	return nil
 }
 
-func (p *pageState) setPages(pages page.Pages) {
-	page.SortByDefault(pages)
-	p.pages = pages
-}
-
 func (p *pageState) renderResources() (err error) {
 	p.resourcesPublishInit.Do(func() {
 		var toBeDeleted []int
@@ -489,13 +520,6 @@ func (p *pageState) addResources(r ...resource.Resource) {
 	p.resources = append(p.resources, r...)
 }
 
-func (p *pageState) addSectionToParent() {
-	if p.parent == nil {
-		return
-	}
-	p.parent.subSections = append(p.parent.subSections, p)
-}
-
 func (p *pageState) mapContent(meta *pageMeta) error {
 
 	s := p.shortcodeState
@@ -743,27 +767,6 @@ func (p *pageState) shiftToOutputFormat(isRenderingSite bool, idx int) error {
 	return nil
 }
 
-func (p *pageState) getTaxonomyNodeInfo() *taxonomyNodeInfo {
-	info := p.s.taxonomyNodes.Get(p.SectionsEntries()...)
-
-	if info == nil {
-		// There can be unused content pages for taxonomies (e.g. author that
-		// has not written anything, yet), and these will not have a taxonomy
-		// node created in the assemble taxonomies step.
-		return nil
-	}
-
-	return info
-
-}
-
-func (p *pageState) sortParentSections() {
-	if p.parent == nil {
-		return
-	}
-	page.SortByDefault(p.parent.subSections)
-}
-
 // sourceRef returns the reference used by GetPage and ref/relref shortcodes to refer to
 // this page. It is prefixed with a "/".
 //