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

resources/page/page.go

@@ -57,6 +57,13 @@ type AuthorProvider interface {
 // ChildCareProvider provides accessors to child resources.
 type ChildCareProvider interface {
 	Pages() Pages
+
+	// RegularPages returns a list of pages of kind 'Page'.
+	// In Hugo 0.57 we changed the Pages method so it returns all page
+	// kinds, even sections. If you want the old behaviour, you can
+	// use RegularPages.
+	RegularPages() Pages
+
 	Resources() resource.Resources
 }
 

resources/page/page_nop.go

@@ -284,6 +284,10 @@ func (p *nopPage) Pages() Pages {
 	return nil
 }
 
+func (p *nopPage) RegularPages() Pages {
+	return nil
+}
+
 func (p *nopPage) Paginate(seq interface{}, options ...interface{}) (*Pager, error) {
 	return nil, nil
 }

resources/page/testhelpers_test.go

@@ -351,6 +351,10 @@ func (p *testPage) Pages() Pages {
 	panic("not implemented")
 }
 
+func (p *testPage) RegularPages() Pages {
+	panic("not implemented")
+}
+
 func (p *testPage) Paginate(seq interface{}, options ...interface{}) (*Pager, error) {
 	return nil, nil
 }

resources/page/weighted.go

@@ -42,7 +42,7 @@ func (p WeightedPages) Page() Page {
 		return nil
 	}
 
-	return first.owner.Page
+	return first.owner
 }
 
 // A WeightedPage is a Page with a weight.
@@ -54,15 +54,10 @@ type WeightedPage struct {
 	// manual .Site.GetPage lookups. It is implemented in this roundabout way
 	// because we cannot add additional state to the WeightedPages slice
 	// without breaking lots of templates in the wild.
-	owner *PageWrapper
+	owner Page
 }
 
-// PageWrapper wraps a Page.
-type PageWrapper struct {
-	Page
-}
-
-func NewWeightedPage(weight int, p Page, owner *PageWrapper) WeightedPage {
+func NewWeightedPage(weight int, p Page, owner Page) WeightedPage {
 	return WeightedPage{Weight: weight, Page: p, owner: owner}
 }