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

8 files changed, 73 insertions, 30 deletions

diff --git a/resources/image_cache.go b/resources/image_cache.go
index f57d73ede..1888b457f 100644
--- a/resources/image_cache.go
+++ b/resources/image_cache.go
@@ -35,32 +35,25 @@ type imageCache struct {
 	store map[string]*resourceAdapter
 }
 
-func (c *imageCache) isInCache(key string) bool {
-	c.mu.RLock()
-	_, found := c.store[c.normalizeKey(key)]
-	c.mu.RUnlock()
-	return found
-}
-
-func (c *imageCache) deleteByPrefix(prefix string) {
+func (c *imageCache) deleteIfContains(s string) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	prefix = c.normalizeKey(prefix)
+	s = c.normalizeKeyBase(s)
 	for k := range c.store {
-		if strings.HasPrefix(k, prefix) {
+		if strings.Contains(k, s) {
 			delete(c.store, k)
 		}
 	}
 }
 
+// The cache key is a lowecase path with Unix style slashes and it always starts with
+// a leading slash.
 func (c *imageCache) normalizeKey(key string) string {
-	// It is a path with Unix style slashes and it always starts with a leading slash.
-	key = filepath.ToSlash(key)
-	if !strings.HasPrefix(key, "/") {
-		key = "/" + key
-	}
+	return "/" + c.normalizeKeyBase(key)
+}
 
-	return key
+func (c *imageCache) normalizeKeyBase(key string) string {
+	return strings.Trim(strings.ToLower(filepath.ToSlash(key)), "/")
 }
 
 func (c *imageCache) clear() {
@@ -74,6 +67,7 @@ func (c *imageCache) getOrCreate(
 	createImage func() (*imageResource, image.Image, error)) (*resourceAdapter, error) {
 	relTarget := parent.relTargetPathFromConfig(conf)
 	memKey := parent.relTargetPathForRel(relTarget.path(), false, false, false)
+	memKey = c.normalizeKey(memKey)
 
 	// For the file cache we want to generate and store it once if possible.
 	fileKeyPath := relTarget
diff --git a/resources/image_test.go b/resources/image_test.go
index c5564a5cb..f98d9f4bb 100644
--- a/resources/image_test.go
+++ b/resources/image_test.go
@@ -598,6 +598,7 @@ func TestImageOperationsGolden(t *testing.T) {
 		}
 
 		resized, err := orig.Fill("400x200 center")
+		c.Assert(err, qt.IsNil)
 
 		for _, filter := range filters {
 			resized, err := resized.Filter(filter)
diff --git a/resources/page/page.go b/resources/page/page.go
index 28094a4a9..c096cb726 100644
--- a/resources/page/page.go
+++ b/resources/page/page.go
@@ -23,8 +23,8 @@ import (
 
 	"github.com/gohugoio/hugo/common/hugo"
 	"github.com/gohugoio/hugo/common/maps"
-
 	"github.com/gohugoio/hugo/compare"
+	"github.com/gohugoio/hugo/hugofs/files"
 
 	"github.com/gohugoio/hugo/navigation"
 	"github.com/gohugoio/hugo/related"
@@ -133,7 +133,7 @@ type PageMetaProvider interface {
 
 	// BundleType returns the bundle type: "leaf", "branch" or an empty string if it is none.
 	// See https://gohugo.io/content-management/page-bundles/
-	BundleType() string
+	BundleType() files.ContentClass
 
 	// A configured description.
 	Description() string
diff --git a/resources/page/page_marshaljson.autogen.go b/resources/page/page_marshaljson.autogen.go
index 6e08210ac..47f385e8a 100644
--- a/resources/page/page_marshaljson.autogen.go
+++ b/resources/page/page_marshaljson.autogen.go
@@ -20,6 +20,7 @@ import (
 	"github.com/bep/gitmap"
 	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/hugofs/files"
 	"github.com/gohugoio/hugo/langs"
 	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/navigation"
@@ -112,7 +113,7 @@ func MarshalPageToJSON(p Page) ([]byte, error) {
 		PublishDate              time.Time
 		ExpiryDate               time.Time
 		Aliases                  []string
-		BundleType               string
+		BundleType               files.ContentClass
 		Description              string
 		Draft                    bool
 		IsHome                   bool
diff --git a/resources/page/page_nop.go b/resources/page/page_nop.go
index 19c7068e0..16663ab39 100644
--- a/resources/page/page_nop.go
+++ b/resources/page/page_nop.go
@@ -19,6 +19,8 @@ import (
 	"html/template"
 	"time"
 
+	"github.com/gohugoio/hugo/hugofs/files"
+
 	"github.com/gohugoio/hugo/hugofs"
 
 	"github.com/bep/gitmap"
@@ -83,7 +85,7 @@ func (p *nopPage) BaseFileName() string {
 	return ""
 }
 
-func (p *nopPage) BundleType() string {
+func (p *nopPage) BundleType() files.ContentClass {
 	return ""
 }
 
diff --git a/resources/page/pagemeta/pagemeta.go b/resources/page/pagemeta/pagemeta.go
index 07e5c5673..1f8afdc18 100644
--- a/resources/page/pagemeta/pagemeta.go
+++ b/resources/page/pagemeta/pagemeta.go
@@ -13,9 +13,59 @@
 
 package pagemeta
 
+import (
+	"github.com/mitchellh/mapstructure"
+)
+
 type URLPath struct {
 	URL       string
 	Permalink string
 	Slug      string
 	Section   string
 }
+
+var defaultBuildConfig = BuildConfig{
+	List:             true,
+	Render:           true,
+	PublishResources: true,
+	set:              true,
+}
+
+// BuildConfig holds configuration options about how to handle a Page in Hugo's
+// build process.
+type BuildConfig struct {
+	// Whether to add it to any of the page collections.
+	// Note that the page can still be found with .Site.GetPage.
+	List bool
+
+	// Whether to render it.
+	Render bool
+
+	// Whether to publish its resources. These will still be published on demand,
+	// but enabling this can be useful if the originals (e.g. images) are
+	// never used.
+	PublishResources bool
+
+	set bool // BuildCfg is non-zero if this is set to true.
+}
+
+// Disable sets all options to their off value.
+func (b *BuildConfig) Disable() {
+	b.List = false
+	b.Render = false
+	b.PublishResources = false
+	b.set = true
+}
+
+func (b BuildConfig) IsZero() bool {
+	return !b.set
+}
+
+func DecodeBuildConfig(m interface{}) (BuildConfig, error) {
+	b := defaultBuildConfig
+	if m == nil {
+		return b, nil
+	}
+	err := mapstructure.WeakDecode(m, &b)
+	return b, err
+}
diff --git a/resources/page/testhelpers_test.go b/resources/page/testhelpers_test.go
index 0d21faa51..dd28fa2cb 100644
--- a/resources/page/testhelpers_test.go
+++ b/resources/page/testhelpers_test.go
@@ -19,6 +19,8 @@ import (
 	"path/filepath"
 	"time"
 
+	"github.com/gohugoio/hugo/hugofs/files"
+
 	"github.com/gohugoio/hugo/modules"
 
 	"github.com/bep/gitmap"
@@ -133,7 +135,7 @@ func (p *testPage) BaseFileName() string {
 	panic("not implemented")
 }
 
-func (p *testPage) BundleType() string {
+func (p *testPage) BundleType() files.ContentClass {
 	panic("not implemented")
 }
 
diff --git a/resources/resource_spec.go b/resources/resource_spec.go
index a992df355..89b28bf83 100644
--- a/resources/resource_spec.go
+++ b/resources/resource_spec.go
@@ -129,15 +129,8 @@ func (r *Spec) ClearCaches() {
 	r.ResourceCache.clear()
 }
 
-func (r *Spec) DeleteCacheByPrefix(prefix string) {
-	r.imageCache.deleteByPrefix(prefix)
-}
-
-// TODO(bep) unify
-func (r *Spec) IsInImageCache(key string) bool {
-	// This is used for cache pruning. We currently only have images, but we could
-	// imagine expanding on this.
-	return r.imageCache.isInCache(key)
+func (r *Spec) DeleteBySubstring(s string) {
+	r.imageCache.deleteIfContains(s)
 }
 
 func (s *Spec) String() string {