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, 12 insertions, 10 deletions

diff --git a/commands/convert.go b/commands/convert.go
index c4f88a245..e7ba572bc 100644
--- a/commands/convert.go
+++ b/commands/convert.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -20,6 +20,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/gohugoio/hugo/resources/page"
+
 	"github.com/gohugoio/hugo/hugofs"
 
 	"github.com/gohugoio/hugo/helpers"
@@ -124,8 +126,8 @@ func (cc *convertCmd) convertContents(format metadecoders.Format) error {
 
 	site := h.Sites[0]
 
-	site.Log.FEEDBACK.Println("processing", len(site.AllPages), "content files")
-	for _, p := range site.AllPages {
+	site.Log.FEEDBACK.Println("processing", len(site.AllPages()), "content files")
+	for _, p := range site.AllPages() {
 		if err := cc.convertAndSavePage(p, site, format); err != nil {
 			return err
 		}
@@ -133,24 +135,24 @@ func (cc *convertCmd) convertContents(format metadecoders.Format) error {
 	return nil
 }
 
-func (cc *convertCmd) convertAndSavePage(p *hugolib.Page, site *hugolib.Site, targetFormat metadecoders.Format) error {
+func (cc *convertCmd) convertAndSavePage(p page.Page, site *hugolib.Site, targetFormat metadecoders.Format) error {
 	// The resources are not in .Site.AllPages.
-	for _, r := range p.Resources.ByType("page") {
-		if err := cc.convertAndSavePage(r.(*hugolib.Page), site, targetFormat); err != nil {
+	for _, r := range p.Resources().ByType("page") {
+		if err := cc.convertAndSavePage(r.(page.Page), site, targetFormat); err != nil {
 			return err
 		}
 	}
 
-	if p.Filename() == "" {
+	if p.File() == nil {
 		// No content file.
 		return nil
 	}
 
 	errMsg := fmt.Errorf("Error processing file %q", p.Path())
 
-	site.Log.INFO.Println("Attempting to convert", p.LogicalName())
+	site.Log.INFO.Println("Attempting to convert", p.File().Filename())
 
-	f, _ := p.File.(src.ReadableFile)
+	f, _ := p.File().(src.ReadableFile)
 	file, err := f.Open()
 	if err != nil {
 		site.Log.ERROR.Println(errMsg)
@@ -186,7 +188,7 @@ func (cc *convertCmd) convertAndSavePage(p *hugolib.Page, site *hugolib.Site, ta
 
 	newContent.Write(pf.content)
 
-	newFilename := p.Filename()
+	newFilename := p.File().Filename()
 
 	if cc.outputDir != "" {
 		contentDir := strings.TrimSuffix(newFilename, p.Path())