Make Page an interface

The main motivation of this commit is to add a `page.Page` interface to replace the very file-oriented `hugolib.Page` struct.
This is all a preparation step for issue  #5074, "pages from other data sources".

But this also fixes a set of annoying limitations, especially related to custom output formats, and shortcodes.

Most notable changes:

* The inner content of shortcodes using the `{{%` as the outer-most delimiter will now be sent to the content renderer, e.g. Blackfriday.
  This means that any markdown will partake in the global ToC and footnote context etc.
* The Custom Output formats are now "fully virtualized". This removes many of the current limitations.
* The taxonomy list type now has a reference to the `Page` object.
  This improves the taxonomy template `.Title` situation and make common template constructs much simpler.

See #5074
Fixes #5763
Fixes #5758
Fixes #5090
Fixes #5204
Fixes #4695
Fixes #5607
Fixes #5707
Fixes #5719
Fixes #3113
Fixes #5706
Fixes #5767
Fixes #5723
Fixes #5769
Fixes #5770
Fixes #5771
Fixes #5759
Fixes #5776
Fixes #5777
Fixes #5778

1 files changed, 148 insertions, 0 deletions

diff --git a/hugolib/page__paths.go b/hugolib/page__paths.go
new file mode 100644
index 000000000..0a5dad5ef
--- /dev/null
+++ b/hugolib/page__paths.go
@@ -0,0 +1,148 @@
+// 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 (
+	"net/url"
+
+	"github.com/gohugoio/hugo/resources/page"
+)
+
+func newPagePaths(
+	s *Site,
+	p page.Page,
+	pm *pageMeta) (pagePaths, error) {
+
+	targetPathDescriptor, err := createTargetPathDescriptor(s, p, pm)
+	if err != nil {
+		return pagePaths{}, err
+	}
+
+	outputFormats := pm.outputFormats()
+	if len(outputFormats) == 0 {
+		outputFormats = pm.s.outputFormats[pm.Kind()]
+	}
+
+	if len(outputFormats) == 0 {
+		return pagePaths{}, nil
+	}
+
+	if pm.headless {
+		outputFormats = outputFormats[:1]
+	}
+
+	pageOutputFormats := make(page.OutputFormats, len(outputFormats))
+	targets := make(map[string]targetPathsHolder)
+
+	for i, f := range outputFormats {
+		desc := targetPathDescriptor
+		desc.Type = f
+		paths := page.CreateTargetPaths(desc)
+
+		var relPermalink, permalink string
+
+		if !pm.headless {
+			relPermalink = paths.RelPermalink(s.PathSpec)
+			permalink = paths.PermalinkForOutputFormat(s.PathSpec, f)
+		}
+
+		pageOutputFormats[i] = page.NewOutputFormat(relPermalink, permalink, len(outputFormats) == 1, f)
+
+		// Use the main format for permalinks, usually HTML.
+		permalinksIndex := 0
+		if f.Permalinkable {
+			// Unless it's permalinkable
+			permalinksIndex = i
+		}
+
+		targets[f.Name] = targetPathsHolder{
+			paths:        paths,
+			OutputFormat: pageOutputFormats[permalinksIndex]}
+
+	}
+
+	return pagePaths{
+		outputFormats:        pageOutputFormats,
+		targetPaths:          targets,
+		targetPathDescriptor: targetPathDescriptor,
+	}, nil
+
+}
+
+type pagePaths struct {
+	outputFormats page.OutputFormats
+
+	targetPaths          map[string]targetPathsHolder
+	targetPathDescriptor page.TargetPathDescriptor
+}
+
+func (l pagePaths) OutputFormats() page.OutputFormats {
+	return l.outputFormats
+}
+
+func createTargetPathDescriptor(s *Site, p page.Page, pm *pageMeta) (page.TargetPathDescriptor, error) {
+	var (
+		dir      string
+		baseName string
+	)
+
+	d := s.Deps
+
+	if p.File() != nil {
+		dir = p.File().Dir()
+		baseName = p.File().TranslationBaseName()
+	}
+
+	alwaysInSubDir := p.Kind() == kindSitemap
+
+	desc := page.TargetPathDescriptor{
+		PathSpec:    d.PathSpec,
+		Kind:        p.Kind(),
+		Sections:    p.SectionsEntries(),
+		UglyURLs:    s.Info.uglyURLs(p),
+		ForcePrefix: s.h.IsMultihost() || alwaysInSubDir,
+		Dir:         dir,
+		URL:         pm.urlPaths.URL,
+	}
+
+	if pm.Slug() != "" {
+		desc.BaseName = pm.Slug()
+	} else {
+		desc.BaseName = baseName
+	}
+
+	desc.PrefixFilePath = s.getLanguageTargetPathLang(alwaysInSubDir)
+	desc.PrefixLink = s.getLanguagePermalinkLang(alwaysInSubDir)
+
+	// Expand only page.KindPage and page.KindTaxonomy; don't expand other Kinds of Pages
+	// like page.KindSection or page.KindTaxonomyTerm because they are "shallower" and
+	// the permalink configuration values are likely to be redundant, e.g.
+	// naively expanding /category/:slug/ would give /category/categories/ for
+	// the "categories" page.KindTaxonomyTerm.
+	if p.Kind() == page.KindPage || p.Kind() == page.KindTaxonomy {
+		opath, err := d.ResourceSpec.Permalinks.Expand(p.Section(), p)
+		if err != nil {
+			return desc, err
+		}
+
+		if opath != "" {
+			opath, _ = url.QueryUnescape(opath)
+			desc.ExpandedPermalink = opath
+		}
+
+	}
+
+	return desc, nil
+
+}