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

2 files changed, 53 insertions, 14 deletions

diff --git a/related/inverted_index.go b/related/inverted_index.go
index 309eb4097..fda6b9222 100644
--- a/related/inverted_index.go
+++ b/related/inverted_index.go
@@ -1,4 +1,4 @@
-// Copyright 2017-present 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.
@@ -106,11 +106,15 @@ type IndexConfig struct {
 
 // Document is the interface an indexable document in Hugo must fulfill.
 type Document interface {
-	// SearchKeywords returns a list of keywords for the given index config.
-	SearchKeywords(cfg IndexConfig) ([]Keyword, error)
+	// RelatedKeywords returns a list of keywords for the given index config.
+	RelatedKeywords(cfg IndexConfig) ([]Keyword, error)
 
 	// When this document was or will be published.
-	PubDate() time.Time
+	PublishDate() time.Time
+
+	// Name is used as an tiebreaker if both Weight and PublishDate are
+	// the same.
+	Name() string
 }
 
 // InvertedIndex holds an inverted index, also sometimes named posting list, which
@@ -164,7 +168,7 @@ func (idx *InvertedIndex) Add(docs ...Document) error {
 
 		for _, doc := range docs {
 			var words []Keyword
-			words, err = doc.SearchKeywords(config)
+			words, err = doc.RelatedKeywords(config)
 			if err != nil {
 				continue
 			}
@@ -211,7 +215,10 @@ func (r ranks) Len() int      { return len(r) }
 func (r ranks) Swap(i, j int) { r[i], r[j] = r[j], r[i] }
 func (r ranks) Less(i, j int) bool {
 	if r[i].Weight == r[j].Weight {
-		return r[i].Doc.PubDate().After(r[j].Doc.PubDate())
+		if r[i].Doc.PublishDate() == r[j].Doc.PublishDate() {
+			return r[i].Doc.Name() < r[j].Doc.Name()
+		}
+		return r[i].Doc.PublishDate().After(r[j].Doc.PublishDate())
 	}
 	return r[i].Weight > r[j].Weight
 }
@@ -241,7 +248,7 @@ func (idx *InvertedIndex) SearchDoc(doc Document, indices ...string) ([]Document
 	}
 
 	for _, cfg := range configs {
-		keywords, err := doc.SearchKeywords(cfg)
+		keywords, err := doc.RelatedKeywords(cfg)
 		if err != nil {
 			return nil, err
 		}
@@ -250,7 +257,7 @@ func (idx *InvertedIndex) SearchDoc(doc Document, indices ...string) ([]Document
 
 	}
 
-	return idx.searchDate(doc.PubDate(), q...)
+	return idx.searchDate(doc.PublishDate(), q...)
 }
 
 // ToKeywords returns a Keyword slice of the given input.
@@ -344,7 +351,7 @@ func (idx *InvertedIndex) searchDate(upperDate time.Time, query ...queryElement)
 				for _, doc := range docs {
 					if applyDateFilter {
 						// Exclude newer than the limit given
-						if doc.PubDate().After(upperDate) {
+						if doc.PublishDate().After(upperDate) {
 							continue
 						}
 					}
diff --git a/related/inverted_index_test.go b/related/inverted_index_test.go
index 2e6b90bbf..4ef27875d 100644
--- a/related/inverted_index_test.go
+++ b/related/inverted_index_test.go
@@ -1,4 +1,4 @@
-// Copyright 2017-present 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.
@@ -25,6 +25,7 @@ import (
 type testDoc struct {
 	keywords map[string][]Keyword
 	date     time.Time
+	name     string
 }
 
 func (d *testDoc) String() string {
@@ -39,11 +40,19 @@ func (d *testDoc) String() string {
 	return s
 }
 
+func (d *testDoc) Name() string {
+	return d.name
+}
+
 func newTestDoc(name string, keywords ...string) *testDoc {
+	time.Sleep(1 * time.Millisecond)
+	return newTestDocWithDate(name, time.Now(), keywords...)
+}
+
+func newTestDocWithDate(name string, date time.Time, keywords ...string) *testDoc {
 	km := make(map[string][]Keyword)
 
-	time.Sleep(1 * time.Millisecond)
-	kw := &testDoc{keywords: km, date: time.Now()}
+	kw := &testDoc{keywords: km, date: date}
 
 	kw.addKeywords(name, keywords...)
 	return kw
@@ -68,11 +77,11 @@ func createTestKeywords(name string, keywords ...string) map[string][]string {
 	}
 }
 
-func (d *testDoc) SearchKeywords(cfg IndexConfig) ([]Keyword, error) {
+func (d *testDoc) RelatedKeywords(cfg IndexConfig) ([]Keyword, error) {
 	return d.keywords[cfg.Name], nil
 }
 
-func (d *testDoc) PubDate() time.Time {
+func (d *testDoc) PublishDate() time.Time {
 	return d.date
 }
 
@@ -167,6 +176,29 @@ func TestSearch(t *testing.T) {
 		assert.Equal(docs[3], m[0])
 	})
 
+	t.Run("searchdoc-keywords-same-date", func(t *testing.T) {
+		assert := require.New(t)
+		idx := NewInvertedIndex(config)
+
+		date := time.Now()
+
+		doc := newTestDocWithDate("keywords", date, "a", "b")
+		doc.name = "thedoc"
+
+		for i := 0; i < 10; i++ {
+			docc := *doc
+			docc.name = fmt.Sprintf("doc%d", i)
+			idx.Add(&docc)
+		}
+
+		m, err := idx.SearchDoc(doc, "keywords")
+		assert.NoError(err)
+		assert.Len(m, 10)
+		for i := 0; i < 10; i++ {
+			assert.Equal(fmt.Sprintf("doc%d", i), m[i].Name())
+		}
+	})
+
 }
 
 func BenchmarkRelatedNewIndex(b *testing.B) {