Introduce a tree map for all content

This commit introduces a new data structure to store pages and their resources.

This data structure is backed by radix trees.

This simplies tree operations, makes all pages a bundle,  and paves the way for #6310.

It also solves a set of annoying issues (see list below).

Not a motivation behind this, but this commit also makes Hugo in general a little bit faster and more memory effective (see benchmarks). Especially for partial rebuilds on content edits, but also when taxonomies is in use.

```
name                                   old time/op    new time/op    delta
SiteNew/Bundle_with_image/Edit-16        1.32ms ± 8%    1.00ms ± 9%  -24.42%  (p=0.029 n=4+4)
SiteNew/Bundle_with_JSON_file/Edit-16    1.28ms ± 0%    0.94ms ± 0%  -26.26%  (p=0.029 n=4+4)
SiteNew/Tags_and_categories/Edit-16      33.9ms ± 2%    21.8ms ± 1%  -35.67%  (p=0.029 n=4+4)
SiteNew/Canonify_URLs/Edit-16            40.6ms ± 1%    37.7ms ± 3%   -7.20%  (p=0.029 n=4+4)
SiteNew/Deep_content_tree/Edit-16        56.7ms ± 0%    51.7ms ± 1%   -8.82%  (p=0.029 n=4+4)
SiteNew/Many_HTML_templates/Edit-16      19.9ms ± 2%    18.3ms ± 3%   -7.64%  (p=0.029 n=4+4)
SiteNew/Page_collections/Edit-16         37.9ms ± 4%    34.0ms ± 2%  -10.28%  (p=0.029 n=4+4)
SiteNew/Bundle_with_image-16             10.7ms ± 0%    10.6ms ± 0%   -1.15%  (p=0.029 n=4+4)
SiteNew/Bundle_with_JSON_file-16         10.8ms ± 0%    10.7ms ± 0%   -1.05%  (p=0.029 n=4+4)
SiteNew/Tags_and_categories-16           43.2ms ± 1%    39.6ms ± 1%   -8.35%  (p=0.029 n=4+4)
SiteNew/Canonify_URLs-16                 47.6ms ± 1%    47.3ms ± 0%     ~     (p=0.057 n=4+4)
SiteNew/Deep_content_tree-16             73.0ms ± 1%    74.2ms ± 1%     ~     (p=0.114 n=4+4)
SiteNew/Many_HTML_templates-16           37.9ms ± 0%    38.1ms ± 1%     ~     (p=0.114 n=4+4)
SiteNew/Page_collections-16              53.6ms ± 1%    54.7ms ± 1%   +2.09%  (p=0.029 n=4+4)

name                                   old alloc/op   new alloc/op   delta
SiteNew/Bundle_with_image/Edit-16         486kB ± 0%     430kB ± 0%  -11.47%  (p=0.029 n=4+4)
SiteNew/Bundle_with_JSON_file/Edit-16     265kB ± 0%     209kB ± 0%  -21.06%  (p=0.029 n=4+4)
SiteNew/Tags_and_categories/Edit-16      13.6MB ± 0%     8.8MB ± 0%  -34.93%  (p=0.029 n=4+4)
SiteNew/Canonify_URLs/Edit-16            66.5MB ± 0%    63.9MB ± 0%   -3.95%  (p=0.029 n=4+4)
SiteNew/Deep_content_tree/Edit-16        28.8MB ± 0%    25.8MB ± 0%  -10.55%  (p=0.029 n=4+4)
SiteNew/Many_HTML_templates/Edit-16      6.16MB ± 0%    5.56MB ± 0%   -9.86%  (p=0.029 n=4+4)
SiteNew/Page_collections/Edit-16         16.9MB ± 0%    16.0MB ± 0%   -5.19%  (p=0.029 n=4+4)
SiteNew/Bundle_with_image-16             2.28MB ± 0%    2.29MB ± 0%   +0.35%  (p=0.029 n=4+4)
SiteNew/Bundle_with_JSON_file-16         2.07MB ± 0%    2.07MB ± 0%     ~     (p=0.114 n=4+4)
SiteNew/Tags_and_categories-16           14.3MB ± 0%    13.2MB ± 0%   -7.30%  (p=0.029 n=4+4)
SiteNew/Canonify_URLs-16                 69.1MB ± 0%    69.0MB ± 0%     ~     (p=0.343 n=4+4)
SiteNew/Deep_content_tree-16             31.3MB ± 0%    31.8MB ± 0%   +1.49%  (p=0.029 n=4+4)
SiteNew/Many_HTML_templates-16           10.8MB ± 0%    10.9MB ± 0%   +1.11%  (p=0.029 n=4+4)
SiteNew/Page_collections-16              21.4MB ± 0%    21.6MB ± 0%   +1.15%  (p=0.029 n=4+4)

name                                   old allocs/op  new allocs/op  delta
SiteNew/Bundle_with_image/Edit-16         4.74k ± 0%     3.86k ± 0%  -18.57%  (p=0.029 n=4+4)
SiteNew/Bundle_with_JSON_file/Edit-16     4.73k ± 0%     3.85k ± 0%  -18.58%  (p=0.029 n=4+4)
SiteNew/Tags_and_categories/Edit-16        301k ± 0%      198k ± 0%  -34.14%  (p=0.029 n=4+4)
SiteNew/Canonify_URLs/Edit-16              389k ± 0%      373k ± 0%   -4.07%  (p=0.029 n=4+4)
SiteNew/Deep_content_tree/Edit-16          338k ± 0%      262k ± 0%  -22.63%  (p=0.029 n=4+4)
SiteNew/Many_HTML_templates/Edit-16        102k ± 0%       88k ± 0%  -13.81%  (p=0.029 n=4+4)
SiteNew/Page_collections/Edit-16           176k ± 0%      152k ± 0%  -13.32%  (p=0.029 n=4+4)
SiteNew/Bundle_with_image-16              26.8k ± 0%     26.8k ± 0%   +0.05%  (p=0.029 n=4+4)
SiteNew/Bundle_with_JSON_file-16          26.8k ± 0%     26.8k ± 0%   +0.05%  (p=0.029 n=4+4)
SiteNew/Tags_and_categories-16             273k ± 0%      245k ± 0%  -10.36%  (p=0.029 n=4+4)
SiteNew/Canonify_URLs-16                   396k ± 0%      398k ± 0%   +0.39%  (p=0.029 n=4+4)
SiteNew/Deep_content_tree-16               317k ± 0%      325k ± 0%   +2.53%  (p=0.029 n=4+4)
SiteNew/Many_HTML_templates-16             146k ± 0%      147k ± 0%   +0.98%  (p=0.029 n=4+4)
SiteNew/Page_collections-16                210k ± 0%      215k ± 0%   +2.44%  (p=0.029 n=4+4)
```

Fixes #6312
Fixes #6087
Fixes #6738
Fixes #6412
Fixes #6743
Fixes #6875
Fixes #6034
Fixes #6902
Fixes #6173
Fixes #6590

1 files changed, 47 insertions, 38 deletions

diff --git a/hugolib/page__tree.go b/hugolib/page__tree.go
index 7bd2874bf..776c92166 100644
--- a/hugolib/page__tree.go
+++ b/hugolib/page__tree.go
@@ -14,8 +14,10 @@
 package hugolib
 
 import (
+	"path"
+	"strings"
+
 	"github.com/gohugoio/hugo/common/types"
-	"github.com/gohugoio/hugo/helpers"
 	"github.com/gohugoio/hugo/resources/page"
 )
 
@@ -28,17 +30,18 @@ func (pt pageTree) IsAncestor(other interface{}) (bool, error) {
 		return false, nil
 	}
 
-	pp, err := unwrapPage(other)
-	if err != nil || pp == nil {
-		return false, err
+	tp, ok := other.(treeRefProvider)
+	if !ok {
+		return false, nil
 	}
 
-	if pt.p.Kind() == page.KindPage && len(pt.p.SectionsEntries()) == len(pp.SectionsEntries()) {
-		// A regular page is never its section's ancestor.
+	ref1, ref2 := pt.p.getTreeRef(), tp.getTreeRef()
+
+	if !ref1.isSection() {
 		return false, nil
 	}
 
-	return helpers.HasStringsPrefix(pp.SectionsEntries(), pt.p.SectionsEntries()), nil
+	return strings.HasPrefix(ref2.key, ref1.key), nil
 }
 
 func (pt pageTree) CurrentSection() page.Page {
@@ -55,35 +58,33 @@ func (pt pageTree) IsDescendant(other interface{}) (bool, error) {
 	if pt.p == nil {
 		return false, nil
 	}
-	pp, err := unwrapPage(other)
-	if err != nil || pp == nil {
-		return false, err
+
+	tp, ok := other.(treeRefProvider)
+	if !ok {
+		return false, nil
 	}
 
-	if pp.Kind() == page.KindPage && len(pt.p.SectionsEntries()) == len(pp.SectionsEntries()) {
-		// A regular page is never its section's descendant.
+	ref1, ref2 := pt.p.getTreeRef(), tp.getTreeRef()
+
+	if !ref2.isSection() {
 		return false, nil
 	}
-	return helpers.HasStringsPrefix(pt.p.SectionsEntries(), pp.SectionsEntries()), nil
-}
 
-func (pt pageTree) FirstSection() page.Page {
-	p := pt.p
+	return strings.HasPrefix(ref1.key, ref2.key), nil
 
-	parent := p.Parent()
+}
 
-	if types.IsNil(parent) || parent.IsHome() {
-		return p
+func (pt pageTree) FirstSection() page.Page {
+	ref := pt.p.getTreeRef()
+	key := ref.key
+	if !ref.isSection() {
+		key = path.Dir(key)
 	}
-
-	for {
-		current := parent
-		parent = parent.Parent()
-		if types.IsNil(parent) || parent.IsHome() {
-			return current
-		}
+	_, b := ref.m.getFirstSection(key)
+	if b == nil {
+		return nil
 	}
-
+	return b.p
 }
 
 func (pt pageTree) InSection(other interface{}) (bool, error) {
@@ -91,16 +92,17 @@ func (pt pageTree) InSection(other interface{}) (bool, error) {
 		return false, nil
 	}
 
-	pp, err := unwrapPage(other)
-	if err != nil {
-		return false, err
-	}
-
-	if pp == nil {
+	tp, ok := other.(treeRefProvider)
+	if !ok {
 		return false, nil
 	}
 
-	return pp.CurrentSection().Eq(pt.p.CurrentSection()), nil
+	ref1, ref2 := pt.p.getTreeRef(), tp.getTreeRef()
+
+	s1, _ := ref1.getCurrentSection()
+	s2, _ := ref2.getCurrentSection()
+
+	return s1 == s2, nil
 
 }
 
@@ -109,15 +111,22 @@ func (pt pageTree) Page() page.Page {
 }
 
 func (pt pageTree) Parent() page.Page {
-	if pt.p.parent != nil {
-		return pt.p.parent
+	p := pt.p
+
+	if p.parent != nil {
+		return p.parent
+	}
+
+	if pt.p.IsHome() {
+		return nil
 	}
 
-	if pt.p.bucket == nil || pt.p.bucket.parent == nil {
+	_, b := p.getTreeRef().getSection()
+	if b == nil {
 		return nil
 	}
 
-	return pt.p.bucket.parent.owner
+	return b.p
 }
 
 func (pt pageTree) Sections() page.Pages {