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, 44 insertions, 42 deletions

diff --git a/hugolib/pagecollections_test.go b/hugolib/pagecollections_test.go
index 2f8b31490..a5a347f83 100644
--- a/hugolib/pagecollections_test.go
+++ b/hugolib/pagecollections_test.go
@@ -1,4 +1,4 @@
-// Copyright 2017 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.
@@ -21,6 +21,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/gohugoio/hugo/resources/page"
+
 	"github.com/gohugoio/hugo/deps"
 	"github.com/stretchr/testify/require"
 )
@@ -98,12 +100,12 @@ func BenchmarkGetPageRegular(b *testing.B) {
 
 type testCase struct {
 	kind          string
-	context       *Page
+	context       page.Page
 	path          []string
 	expectedTitle string
 }
 
-func (t *testCase) check(p *Page, err error, errorMsg string, assert *require.Assertions) {
+func (t *testCase) check(p page.Page, err error, errorMsg string, assert *require.Assertions) {
 	switch t.kind {
 	case "Ambiguous":
 		assert.Error(err)
@@ -114,8 +116,8 @@ func (t *testCase) check(p *Page, err error, errorMsg string, assert *require.As
 	default:
 		assert.NoError(err, errorMsg)
 		assert.NotNil(p, errorMsg)
-		assert.Equal(t.kind, p.Kind, errorMsg)
-		assert.Equal(t.expectedTitle, p.title, errorMsg)
+		assert.Equal(t.kind, p.Kind(), errorMsg)
+		assert.Equal(t.expectedTitle, p.Title(), errorMsg)
 	}
 }
 
@@ -159,62 +161,62 @@ func TestGetPage(t *testing.T) {
 
 	tests := []testCase{
 		// legacy content root relative paths
-		{KindHome, nil, []string{}, "home page"},
-		{KindPage, nil, []string{"about.md"}, "about page"},
-		{KindSection, nil, []string{"sect3"}, "section 3"},
-		{KindPage, nil, []string{"sect3/page1.md"}, "Title3_1"},
-		{KindPage, nil, []string{"sect4/page2.md"}, "Title4_2"},
-		{KindSection, nil, []string{"sect3/sect7"}, "another sect7"},
-		{KindPage, nil, []string{"sect3/subsect/deep.md"}, "deep page"},
-		{KindPage, nil, []string{filepath.FromSlash("sect5/page3.md")}, "Title5_3"}, //test OS-specific path
+		{page.KindHome, nil, []string{}, "home page"},
+		{page.KindPage, nil, []string{"about.md"}, "about page"},
+		{page.KindSection, nil, []string{"sect3"}, "section 3"},
+		{page.KindPage, nil, []string{"sect3/page1.md"}, "Title3_1"},
+		{page.KindPage, nil, []string{"sect4/page2.md"}, "Title4_2"},
+		{page.KindSection, nil, []string{"sect3/sect7"}, "another sect7"},
+		{page.KindPage, nil, []string{"sect3/subsect/deep.md"}, "deep page"},
+		{page.KindPage, nil, []string{filepath.FromSlash("sect5/page3.md")}, "Title5_3"}, //test OS-specific path
 
 		// shorthand refs (potentially ambiguous)
-		{KindPage, nil, []string{"unique.md"}, "UniqueBase"},
+		{page.KindPage, nil, []string{"unique.md"}, "UniqueBase"},
 		{"Ambiguous", nil, []string{"page1.md"}, ""},
 
 		// ISSUE: This is an ambiguous ref, but because we have to support the legacy
 		// content root relative paths without a leading slash, the lookup
 		// returns /sect7. This undermines ambiguity detection, but we have no choice.
 		//{"Ambiguous", nil, []string{"sect7"}, ""},
-		{KindSection, nil, []string{"sect7"}, "Sect7s"},
+		{page.KindSection, nil, []string{"sect7"}, "Sect7s"},
 
 		// absolute paths
-		{KindHome, nil, []string{"/"}, "home page"},
-		{KindPage, nil, []string{"/about.md"}, "about page"},
-		{KindSection, nil, []string{"/sect3"}, "section 3"},
-		{KindPage, nil, []string{"/sect3/page1.md"}, "Title3_1"},
-		{KindPage, nil, []string{"/sect4/page2.md"}, "Title4_2"},
-		{KindSection, nil, []string{"/sect3/sect7"}, "another sect7"},
-		{KindPage, nil, []string{"/sect3/subsect/deep.md"}, "deep page"},
-		{KindPage, nil, []string{filepath.FromSlash("/sect5/page3.md")}, "Title5_3"}, //test OS-specific path
-		{KindPage, nil, []string{"/sect3/unique.md"}, "UniqueBase"},                  //next test depends on this page existing
+		{page.KindHome, nil, []string{"/"}, "home page"},
+		{page.KindPage, nil, []string{"/about.md"}, "about page"},
+		{page.KindSection, nil, []string{"/sect3"}, "section 3"},
+		{page.KindPage, nil, []string{"/sect3/page1.md"}, "Title3_1"},
+		{page.KindPage, nil, []string{"/sect4/page2.md"}, "Title4_2"},
+		{page.KindSection, nil, []string{"/sect3/sect7"}, "another sect7"},
+		{page.KindPage, nil, []string{"/sect3/subsect/deep.md"}, "deep page"},
+		{page.KindPage, nil, []string{filepath.FromSlash("/sect5/page3.md")}, "Title5_3"}, //test OS-specific path
+		{page.KindPage, nil, []string{"/sect3/unique.md"}, "UniqueBase"},                  //next test depends on this page existing
 		// {"NoPage", nil, []string{"/unique.md"}, ""},  // ISSUE #4969: this is resolving to /sect3/unique.md
 		{"NoPage", nil, []string{"/missing-page.md"}, ""},
 		{"NoPage", nil, []string{"/missing-section"}, ""},
 
 		// relative paths
-		{KindHome, sec3, []string{".."}, "home page"},
-		{KindHome, sec3, []string{"../"}, "home page"},
-		{KindPage, sec3, []string{"../about.md"}, "about page"},
-		{KindSection, sec3, []string{"."}, "section 3"},
-		{KindSection, sec3, []string{"./"}, "section 3"},
-		{KindPage, sec3, []string{"page1.md"}, "Title3_1"},
-		{KindPage, sec3, []string{"./page1.md"}, "Title3_1"},
-		{KindPage, sec3, []string{"../sect4/page2.md"}, "Title4_2"},
-		{KindSection, sec3, []string{"sect7"}, "another sect7"},
-		{KindSection, sec3, []string{"./sect7"}, "another sect7"},
-		{KindPage, sec3, []string{"./subsect/deep.md"}, "deep page"},
-		{KindPage, sec3, []string{"./subsect/../../sect7/page9.md"}, "Title7_9"},
-		{KindPage, sec3, []string{filepath.FromSlash("../sect5/page3.md")}, "Title5_3"}, //test OS-specific path
-		{KindPage, sec3, []string{"./unique.md"}, "UniqueBase"},
+		{page.KindHome, sec3, []string{".."}, "home page"},
+		{page.KindHome, sec3, []string{"../"}, "home page"},
+		{page.KindPage, sec3, []string{"../about.md"}, "about page"},
+		{page.KindSection, sec3, []string{"."}, "section 3"},
+		{page.KindSection, sec3, []string{"./"}, "section 3"},
+		{page.KindPage, sec3, []string{"page1.md"}, "Title3_1"},
+		{page.KindPage, sec3, []string{"./page1.md"}, "Title3_1"},
+		{page.KindPage, sec3, []string{"../sect4/page2.md"}, "Title4_2"},
+		{page.KindSection, sec3, []string{"sect7"}, "another sect7"},
+		{page.KindSection, sec3, []string{"./sect7"}, "another sect7"},
+		{page.KindPage, sec3, []string{"./subsect/deep.md"}, "deep page"},
+		{page.KindPage, sec3, []string{"./subsect/../../sect7/page9.md"}, "Title7_9"},
+		{page.KindPage, sec3, []string{filepath.FromSlash("../sect5/page3.md")}, "Title5_3"}, //test OS-specific path
+		{page.KindPage, sec3, []string{"./unique.md"}, "UniqueBase"},
 		{"NoPage", sec3, []string{"./sect2"}, ""},
 		//{"NoPage", sec3, []string{"sect2"}, ""}, // ISSUE: /sect3 page relative query is resolving to /sect2
 
 		// absolute paths ignore context
-		{KindHome, sec3, []string{"/"}, "home page"},
-		{KindPage, sec3, []string{"/about.md"}, "about page"},
-		{KindPage, sec3, []string{"/sect4/page2.md"}, "Title4_2"},
-		{KindPage, sec3, []string{"/sect3/subsect/deep.md"}, "deep page"}, //next test depends on this page existing
+		{page.KindHome, sec3, []string{"/"}, "home page"},
+		{page.KindPage, sec3, []string{"/about.md"}, "about page"},
+		{page.KindPage, sec3, []string{"/sect4/page2.md"}, "Title4_2"},
+		{page.KindPage, sec3, []string{"/sect3/subsect/deep.md"}, "deep page"}, //next test depends on this page existing
 		{"NoPage", sec3, []string{"/subsect/deep.md"}, ""},
 	}