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

38 files changed, 4400 insertions, 2261 deletions

diff --git a/hugolib/alias.go b/hugolib/alias.go
index 9eba8b335..b97094ecc 100644
--- a/hugolib/alias.go
+++ b/hugolib/alias.go
@@ -17,7 +17,6 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"html/template"
 	"io"
 	"path"
 	"path/filepath"
@@ -32,8 +31,6 @@ import (
 	"github.com/gohugoio/hugo/tpl"
 )
 
-var defaultAliasTemplates *template.Template
-
 type aliasHandler struct {
 	t         tpl.TemplateHandler
 	log       *loggers.Logger
diff --git a/hugolib/cascade_test.go b/hugolib/cascade_test.go
index 9cd402d6a..dd3aa72a6 100644
--- a/hugolib/cascade_test.go
+++ b/hugolib/cascade_test.go
@@ -17,6 +17,7 @@ import (
 	"bytes"
 	"fmt"
 	"path"
+	"strings"
 	"testing"
 
 	qt "github.com/frankban/quicktest"
@@ -60,29 +61,33 @@ func TestCascade(t *testing.T) {
 		b.Build(BuildCfg{})
 
 		b.AssertFileContent("public/index.html", `
-        12|taxonomy|categories/cool/_index.md|Cascade Category|cat.png|categories|HTML-|
-        12|taxonomy|categories/catsect1|catsect1|cat.png|categories|HTML-|
-        12|taxonomy|categories/funny|funny|cat.png|categories|HTML-|
-        12|taxonomyTerm|categories/_index.md|My Categories|cat.png|categories|HTML-|
-        32|taxonomy|categories/sad/_index.md|Cascade Category|sad.png|categories|HTML-|
-        42|taxonomy|tags/blue|blue|home.png|tags|HTML-|
-        42|section|sect3|Cascade Home|home.png|sect3|HTML-|
-        42|taxonomyTerm|tags|Cascade Home|home.png|tags|HTML-|
-        42|page|bundle1/index.md|Cascade Home|home.png|page|HTML-|
-        42|page|p2.md|Cascade Home|home.png|page|HTML-|
-        42|page|sect2/p2.md|Cascade Home|home.png|sect2|HTML-|
-        42|page|sect3/p1.md|Cascade Home|home.png|sect3|HTML-|
-        42|taxonomy|tags/green|green|home.png|tags|HTML-|
-        42|home|_index.md|Home|home.png|page|HTML-|
-        42|page|p1.md|p1|home.png|page|HTML-|
-        42|section|sect1/_index.md|Sect1|sect1.png|stype|HTML-|
-        42|section|sect1/s1_2/_index.md|Sect1_2|sect1.png|stype|HTML-|
-        42|page|sect1/s1_2/p1.md|Sect1_2_p1|sect1.png|stype|HTML-|
-        42|page|sect1/s1_2/p2.md|Sect1_2_p2|sect1.png|stype|HTML-|
-        42|section|sect2/_index.md|Sect2|home.png|sect2|HTML-|
-        42|page|sect2/p1.md|Sect2_p1|home.png|sect2|HTML-|
-        52|page|sect4/p1.md|Cascade Home|home.png|sect4|RSS-|
-        52|section|sect4/_index.md|Sect4|home.png|sect4|RSS-|
+12|taxonomy|categories/cool/_index.md|Cascade Category|cat.png|categories|HTML-|
+12|taxonomy|categories/catsect1|catsect1|cat.png|categories|HTML-|
+12|taxonomy|categories/funny|funny|cat.png|categories|HTML-|
+12|taxonomyTerm|categories/_index.md|My Categories|cat.png|categories|HTML-|
+32|taxonomy|categories/sad/_index.md|Cascade Category|sad.png|categories|HTML-|
+42|taxonomy|tags/blue|blue|home.png|tags|HTML-|
+42|taxonomyTerm|tags|Cascade Home|home.png|tags|HTML-|
+42|section|sectnocontent|Cascade Home|home.png|sectnocontent|HTML-|
+42|section|sect3|Cascade Home|home.png|sect3|HTML-|
+42|page|bundle1/index.md|Cascade Home|home.png|page|HTML-|
+42|page|p2.md|Cascade Home|home.png|page|HTML-|
+42|page|sect2/p2.md|Cascade Home|home.png|sect2|HTML-|
+42|page|sect3/nofrontmatter.md|Cascade Home|home.png|sect3|HTML-|
+42|page|sect3/p1.md|Cascade Home|home.png|sect3|HTML-|
+42|page|sectnocontent/p1.md|Cascade Home|home.png|sectnocontent|HTML-|
+42|section|sectnofrontmatter/_index.md|Cascade Home|home.png|sectnofrontmatter|HTML-|
+42|taxonomy|tags/green|green|home.png|tags|HTML-|
+42|home|_index.md|Home|home.png|page|HTML-|
+42|page|p1.md|p1|home.png|page|HTML-|
+42|section|sect1/_index.md|Sect1|sect1.png|stype|HTML-|
+42|section|sect1/s1_2/_index.md|Sect1_2|sect1.png|stype|HTML-|
+42|page|sect1/s1_2/p1.md|Sect1_2_p1|sect1.png|stype|HTML-|
+42|page|sect1/s1_2/p2.md|Sect1_2_p2|sect1.png|stype|HTML-|
+42|section|sect2/_index.md|Sect2|home.png|sect2|HTML-|
+42|page|sect2/p1.md|Sect2_p1|home.png|sect2|HTML-|
+52|page|sect4/p1.md|Cascade Home|home.png|sect4|RSS-|
+52|section|sect4/_index.md|Sect4|home.png|sect4|RSS-|
 `)
 
 		// Check that type set in cascade gets the correct layout.
@@ -106,43 +111,131 @@ func TestCascadeEdit(t *testing.T) {
 title: P1
 ---
 `
-	b := newTestSitesBuilder(t).Running()
-	b.WithTemplatesAdded("_default/single.html", `Banner: {{ .Params.banner }}|Layout: {{ .Layout }}|Type: {{ .Type }}|Content: {{ .Content }}`)
-	b.WithContent("post/_index.md", `
+
+	indexContentNoCascade := `
+---
+title: Home
+---
+`
+
+	indexContentCascade := `
 ---
-title: Post
+title: Section
 cascade:
   banner: post.jpg
   layout: postlayout
   type: posttype
 ---
-`)
+`
 
-	b.WithContent("post/dir/_index.md", `
----
-title: Dir
----
-`, "post/dir/p1.md", p1Content)
-	b.Build(BuildCfg{})
+	layout := `Banner: {{ .Params.banner }}|Layout: {{ .Layout }}|Type: {{ .Type }}|Content: {{ .Content }}`
+
+	newSite := func(t *testing.T, cascade bool) *sitesBuilder {
+		b := newTestSitesBuilder(t).Running()
+		b.WithTemplates("_default/single.html", layout)
+		b.WithTemplates("_default/list.html", layout)
+		if cascade {
+			b.WithContent("post/_index.md", indexContentCascade)
+		} else {
+			b.WithContent("post/_index.md", indexContentNoCascade)
+		}
+		b.WithContent("post/dir/p1.md", p1Content)
 
-	assert := func() {
-		b.Helper()
+		return b
+	}
+
+	t.Run("Edit descendant", func(t *testing.T) {
+		t.Parallel()
+
+		b := newSite(t, true)
+		b.Build(BuildCfg{})
+
+		assert := func() {
+			b.Helper()
+			b.AssertFileContent("public/post/dir/p1/index.html",
+				`Banner: post.jpg|`,
+				`Layout: postlayout`,
+				`Type: posttype`,
+			)
+		}
+
+		assert()
+
+		b.EditFiles("content/post/dir/p1.md", p1Content+"\ncontent edit")
+		b.Build(BuildCfg{})
+
+		assert()
 		b.AssertFileContent("public/post/dir/p1/index.html",
-			`Banner: post.jpg|`,
-			`Layout: postlayout`,
-			`Type: posttype`,
+			`content edit
+Banner: post.jpg`,
 		)
-	}
+	})
+
+	t.Run("Edit ancestor", func(t *testing.T) {
+		t.Parallel()
 
-	assert()
+		b := newSite(t, true)
+		b.Build(BuildCfg{})
 
-	b.EditFiles("content/post/dir/p1.md", p1Content+"\ncontent edit")
-	b.Build(BuildCfg{})
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: post.jpg|Layout: postlayout|Type: posttype|Content:`)
 
-	assert()
-	b.AssertFileContent("public/post/dir/p1/index.html",
-		`content edit`,
-	)
+		b.EditFiles("content/post/_index.md", strings.Replace(indexContentCascade, "post.jpg", "edit.jpg", 1))
+
+		b.Build(BuildCfg{})
+
+		b.AssertFileContent("public/post/index.html", `Banner: edit.jpg|Layout: postlayout|Type: posttype|`)
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: edit.jpg|Layout: postlayout|Type: posttype|`)
+	})
+
+	t.Run("Edit ancestor, add cascade", func(t *testing.T) {
+		t.Parallel()
+
+		b := newSite(t, true)
+		b.Build(BuildCfg{})
+
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: post.jpg`)
+
+		b.EditFiles("content/post/_index.md", indexContentCascade)
+
+		b.Build(BuildCfg{})
+
+		b.AssertFileContent("public/post/index.html", `Banner: post.jpg|Layout: postlayout|Type: posttype|`)
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: post.jpg|Layout: postlayout|`)
+	})
+
+	t.Run("Edit ancestor, remove cascade", func(t *testing.T) {
+		t.Parallel()
+
+		b := newSite(t, false)
+		b.Build(BuildCfg{})
+
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: |Layout: |`)
+
+		b.EditFiles("content/post/_index.md", indexContentNoCascade)
+
+		b.Build(BuildCfg{})
+
+		b.AssertFileContent("public/post/index.html", `Banner: |Layout: |Type: post|`)
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: |Layout: |`)
+	})
+
+	t.Run("Edit ancestor, content only", func(t *testing.T) {
+		t.Parallel()
+
+		b := newSite(t, true)
+		b.Build(BuildCfg{})
+
+		b.EditFiles("content/post/_index.md", indexContentCascade+"\ncontent edit")
+
+		counters := &testCounters{}
+		b.Build(BuildCfg{testCounters: counters})
+		// As we only changed the content, not the cascade front matter, make
+		// only the home page is re-rendered.
+		b.Assert(int(counters.contentRenderCounter), qt.Equals, 1)
+
+		b.AssertFileContent("public/post/index.html", `Banner: post.jpg|Layout: postlayout|Type: posttype|Content: <p>content edit</p>`)
+		b.AssertFileContent("public/post/dir/p1/index.html", `Banner: post.jpg|Layout: postlayout|`)
+	})
 }
 
 func newCascadeTestBuilder(t testing.TB, langs []string) *sitesBuilder {
@@ -247,6 +340,12 @@ defaultContentLanguageInSubDir = false
 			}),
 			"sect2/p2.md", p(map[string]interface{}{}),
 			"sect3/p1.md", p(map[string]interface{}{}),
+
+			// No front matter, see #6855
+			"sect3/nofrontmatter.md", `**Hello**`,
+			"sectnocontent/p1.md", `**Hello**`,
+			"sectnofrontmatter/_index.md", `**Hello**`,
+
 			"sect4/_index.md", p(map[string]interface{}{
 				"title": "Sect4",
 				"cascade": map[string]interface{}{
diff --git a/hugolib/content_map.go b/hugolib/content_map.go
new file mode 100644
index 000000000..f0b66d859
--- /dev/null
+++ b/hugolib/content_map.go
@@ -0,0 +1,971 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hugolib
+
+import (
+	"fmt"
+	"path"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"github.com/gohugoio/hugo/resources/page"
+	"github.com/pkg/errors"
+
+	"github.com/gohugoio/hugo/hugofs/files"
+
+	"github.com/gohugoio/hugo/hugofs"
+
+	radix "github.com/armon/go-radix"
+)
+
+// We store the branch nodes in either the `sections` or `taxonomies` tree
+// with their path as a key; Unix style slashes, a leading slash but no
+// trailing slash.
+//
+// E.g. "/blog" or "/categories/funny"
+//
+// Pages that belongs to a section are stored in the `pages` tree below
+// the section name and a branch separator, e.g. "/blog__hb_". A page is
+// given a key using the path below the section and the base filename with no extension
+// with a leaf separator added.
+//
+// For bundled pages (/mybundle/index.md), we use the folder name.
+//
+// An exmple of a full page key would be "/blog__hb_/page1__hl_"
+//
+// Bundled resources are stored in the `resources` having their path prefixed
+// with the bundle they belong to, e.g.
+// "/blog__hb_/bundle__hl_data.json".
+//
+// The weighted taxonomy entries extracted from page front matter are stored in
+// the `taxonomyEntries` tree below /plural/term/page-key, e.g.
+// "/categories/funny/blog__hb_/bundle__hl_".
+const (
+	cmBranchSeparator = "__hb_"
+	cmLeafSeparator   = "__hl_"
+)
+
+// Used to mark ambigous keys in reverse index lookups.
+var ambigousContentNode = &contentNode{}
+
+func newContentMap(cfg contentMapConfig) *contentMap {
+	m := &contentMap{
+		cfg:             &cfg,
+		pages:           &contentTree{Name: "pages", Tree: radix.New()},
+		sections:        &contentTree{Name: "sections", Tree: radix.New()},
+		taxonomies:      &contentTree{Name: "taxonomies", Tree: radix.New()},
+		taxonomyEntries: &contentTree{Name: "taxonomyEntries", Tree: radix.New()},
+		resources:       &contentTree{Name: "resources", Tree: radix.New()},
+	}
+
+	m.pageTrees = []*contentTree{
+		m.pages, m.sections, m.taxonomies,
+	}
+
+	m.bundleTrees = []*contentTree{
+		m.pages, m.sections, m.taxonomies, m.resources,
+	}
+
+	m.branchTrees = []*contentTree{
+		m.sections, m.taxonomies,
+	}
+
+	addToReverseMap := func(k string, n *contentNode, m map[interface{}]*contentNode) {
+		k = strings.ToLower(k)
+		existing, found := m[k]
+		if found && existing != ambigousContentNode {
+			m[k] = ambigousContentNode
+		} else if !found {
+			m[k] = n
+		}
+	}
+
+	m.pageReverseIndex = &contentTreeReverseIndex{
+		t: []*contentTree{m.pages, m.sections, m.taxonomies},
+		initFn: func(t *contentTree, m map[interface{}]*contentNode) {
+			t.Walk(func(s string, v interface{}) bool {
+				n := v.(*contentNode)
+				if n.p != nil && !n.p.File().IsZero() {
+					meta := n.p.File().FileInfo().Meta()
+					if meta.Path() != meta.PathFile() {
+						// Keep track of the original mount source.
+						mountKey := filepath.ToSlash(filepath.Join(meta.Module(), meta.PathFile()))
+						addToReverseMap(mountKey, n, m)
+					}
+				}
+				k := strings.TrimSuffix(path.Base(s), cmLeafSeparator)
+				addToReverseMap(k, n, m)
+				return false
+			})
+		},
+	}
+
+	return m
+}
+
+type cmInsertKeyBuilder struct {
+	m *contentMap
+
+	err error
+
+	// Builder state
+	tree    *contentTree
+	baseKey string // Section or page key
+	key     string
+}
+
+func (b cmInsertKeyBuilder) ForPage(s string) *cmInsertKeyBuilder {
+	// TODO2 fmt.Println("ForPage:", s, "baseKey:", b.baseKey, "key:", b.key)
+	baseKey := b.baseKey
+	b.baseKey = s
+
+	if !strings.HasPrefix(s, "/") {
+		s = "/" + s
+	}
+
+	if baseKey != "/" {
+		// Don't repeat the section path in the key.
+		s = strings.TrimPrefix(s, baseKey)
+	}
+
+	switch b.tree {
+	case b.m.sections:
+		b.tree = b.m.pages
+		b.key = baseKey + cmBranchSeparator + s + cmLeafSeparator
+	case b.m.taxonomies:
+		b.key = path.Join(baseKey, s)
+	default:
+		panic("invalid state")
+	}
+
+	return &b
+}
+
+func (b cmInsertKeyBuilder) ForResource(s string) *cmInsertKeyBuilder {
+	// TODO2 fmt.Println("ForResource:", s, "baseKey:", b.baseKey, "key:", b.key)
+
+	s = strings.TrimPrefix(s, "/")
+	s = strings.TrimPrefix(s, strings.TrimPrefix(b.baseKey, "/")+"/")
+
+	switch b.tree {
+	case b.m.pages:
+		b.key = b.key + s
+	case b.m.sections, b.m.taxonomies:
+		b.key = b.key + cmLeafSeparator + s
+	default:
+		panic(fmt.Sprintf("invalid state: %#v", b.tree))
+	}
+	b.tree = b.m.resources
+	return &b
+}
+
+func (b *cmInsertKeyBuilder) Insert(n *contentNode) *cmInsertKeyBuilder {
+	if b.err == nil {
+		b.tree.Insert(cleanTreeKey(b.key), n)
+	}
+	return b
+}
+
+func (b *cmInsertKeyBuilder) DeleteAll() *cmInsertKeyBuilder {
+	if b.err == nil {
+		b.tree.DeletePrefix(cleanTreeKey(b.key))
+	}
+	return b
+}
+
+func (b *cmInsertKeyBuilder) WithFile(fi hugofs.FileMetaInfo) *cmInsertKeyBuilder {
+	b.newTopLevel()
+	m := b.m
+	meta := fi.Meta()
+	p := cleanTreeKey(meta.Path())
+	bundlePath := m.getBundleDir(meta)
+	isBundle := meta.Classifier().IsBundle()
+	if isBundle {
+		panic("not implemented")
+	}
+
+	p, k := b.getBundle(p)
+	if k == "" {
+		b.err = errors.Errorf("no bundle header found for %q", bundlePath)
+		return b
+	}
+
+	id := k + m.reduceKeyPart(p, fi.Meta().Path())
+	b.tree = b.m.resources
+	b.key = id
+	b.baseKey = p
+
+	return b
+}
+
+func (b *cmInsertKeyBuilder) WithSection(s string) *cmInsertKeyBuilder {
+	b.newTopLevel()
+	b.tree = b.m.sections
+	b.baseKey = s
+	b.key = s
+	// TODO2 fmt.Println("WithSection:", s, "baseKey:", b.baseKey, "key:", b.key)
+	return b
+}
+
+func (b *cmInsertKeyBuilder) WithTaxonomy(s string) *cmInsertKeyBuilder {
+	b.newTopLevel()
+	b.tree = b.m.taxonomies
+	b.baseKey = s
+	b.key = s
+	return b
+}
+
+// getBundle gets both the key to the section and the prefix to where to store
+// this page bundle and its resources.
+func (b *cmInsertKeyBuilder) getBundle(s string) (string, string) {
+	m := b.m
+	section, _ := m.getSection(s)
+
+	p := s
+	if section != "/" {
+		p = strings.TrimPrefix(s, section)
+	}
+
+	bundlePathParts := strings.Split(p, "/")[1:]
+	basePath := section + cmBranchSeparator
+
+	// Put it into an existing bundle if found.
+	for i := len(bundlePathParts) - 2; i >= 0; i-- {
+		bundlePath := path.Join(bundlePathParts[:i]...)
+		searchKey := basePath + "/" + bundlePath + cmLeafSeparator
+		if _, found := m.pages.Get(searchKey); found {
+			return section + "/" + bundlePath, searchKey
+		}
+	}
+
+	// Put it into the section bundle.
+	return section, section + cmLeafSeparator
+}
+