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

7 files changed, 59 insertions, 28 deletions

diff --git a/helpers/content.go b/helpers/content.go
index 644942cb1..bc19f6559 100644
--- a/helpers/content.go
+++ b/helpers/content.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.
@@ -57,7 +57,7 @@ type ContentSpec struct {
 	Highlight            func(code, lang, optsStr string) (string, error)
 	defatultPygmentsOpts map[string]string
 
-	cfg config.Provider
+	Cfg config.Provider
 }
 
 // NewContentSpec returns a ContentSpec initialized
@@ -73,7 +73,7 @@ func NewContentSpec(cfg config.Provider) (*ContentSpec, error) {
 		BuildExpired:               cfg.GetBool("buildExpired"),
 		BuildDrafts:                cfg.GetBool("buildDrafts"),
 
-		cfg: cfg,
+		Cfg: cfg,
 	}
 
 	// Highlighting setup
@@ -382,7 +382,7 @@ func (c *ContentSpec) getMmarkHTMLRenderer(defaultFlags int, ctx *RenderingConte
 	return &HugoMmarkHTMLRenderer{
 		cs:       c,
 		Renderer: mmark.HtmlRendererWithParameters(htmlFlags, "", "", renderParameters),
-		Cfg:      c.cfg,
+		Cfg:      c.Cfg,
 	}
 }
 
diff --git a/helpers/content_renderer_test.go b/helpers/content_renderer_test.go
index a01014b4e..f542d5d54 100644
--- a/helpers/content_renderer_test.go
+++ b/helpers/content_renderer_test.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.
@@ -24,7 +24,7 @@ import (
 
 // Renders a codeblock using Blackfriday
 func (c ContentSpec) render(input string) string {
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	render := c.getHTMLRenderer(0, ctx)
 
 	buf := &bytes.Buffer{}
@@ -34,7 +34,7 @@ func (c ContentSpec) render(input string) string {
 
 // Renders a codeblock using Mmark
 func (c ContentSpec) renderWithMmark(input string) string {
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	render := c.getMmarkHTMLRenderer(0, ctx)
 
 	buf := &bytes.Buffer{}
diff --git a/helpers/content_test.go b/helpers/content_test.go
index 5297df2de..1dd4a2fb8 100644
--- a/helpers/content_test.go
+++ b/helpers/content_test.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.
@@ -181,7 +181,7 @@ func TestTruncateWordsByRune(t *testing.T) {
 
 func TestGetHTMLRendererFlags(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	renderer := c.getHTMLRenderer(blackfriday.HTML_USE_XHTML, ctx)
 	flags := renderer.GetFlags()
 	if flags&blackfriday.HTML_USE_XHTML != blackfriday.HTML_USE_XHTML {
@@ -210,7 +210,7 @@ func TestGetHTMLRendererAllFlags(t *testing.T) {
 		{blackfriday.HTML_SMARTYPANTS_LATEX_DASHES},
 	}
 	defaultFlags := blackfriday.HTML_USE_XHTML
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Config.AngledQuotes = true
 	ctx.Config.Fractions = true
 	ctx.Config.HrefTargetBlank = true
@@ -235,7 +235,7 @@ func TestGetHTMLRendererAllFlags(t *testing.T) {
 
 func TestGetHTMLRendererAnchors(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.DocumentID = "testid"
 	ctx.Config.PlainIDAnchors = false
 
@@ -259,7 +259,7 @@ func TestGetHTMLRendererAnchors(t *testing.T) {
 
 func TestGetMmarkHTMLRenderer(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.DocumentID = "testid"
 	ctx.Config.PlainIDAnchors = false
 	actualRenderer := c.getMmarkHTMLRenderer(0, ctx)
@@ -283,7 +283,7 @@ func TestGetMmarkHTMLRenderer(t *testing.T) {
 
 func TestGetMarkdownExtensionsMasksAreRemovedFromExtensions(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{"headerId"}
 	ctx.Config.ExtensionsMask = []string{"noIntraEmphasis"}
 
@@ -298,7 +298,7 @@ func TestGetMarkdownExtensionsByDefaultAllExtensionsAreEnabled(t *testing.T) {
 		testFlag int
 	}
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{""}
 	ctx.Config.ExtensionsMask = []string{""}
 	allExtensions := []data{
@@ -330,7 +330,7 @@ func TestGetMarkdownExtensionsByDefaultAllExtensionsAreEnabled(t *testing.T) {
 
 func TestGetMarkdownExtensionsAddingFlagsThroughRenderingContext(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{"definitionLists"}
 	ctx.Config.ExtensionsMask = []string{""}
 
@@ -342,7 +342,7 @@ func TestGetMarkdownExtensionsAddingFlagsThroughRenderingContext(t *testing.T) {
 
 func TestGetMarkdownRenderer(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Content = []byte("testContent")
 	actualRenderedMarkdown := c.markdownRender(ctx)
 	expectedRenderedMarkdown := []byte("<p>testContent</p>\n")
@@ -353,7 +353,7 @@ func TestGetMarkdownRenderer(t *testing.T) {
 
 func TestGetMarkdownRendererWithTOC(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{RenderTOC: true, Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{RenderTOC: true, Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Content = []byte("testContent")
 	actualRenderedMarkdown := c.markdownRender(ctx)
 	expectedRenderedMarkdown := []byte("<nav>\n</nav>\n\n<p>testContent</p>\n")
@@ -368,7 +368,7 @@ func TestGetMmarkExtensions(t *testing.T) {
 		testFlag int
 	}
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Config.Extensions = []string{"tables"}
 	ctx.Config.ExtensionsMask = []string{""}
 	allExtensions := []data{
@@ -397,7 +397,7 @@ func TestGetMmarkExtensions(t *testing.T) {
 
 func TestMmarkRender(t *testing.T) {
 	c := newTestContentSpec()
-	ctx := &RenderingContext{Cfg: c.cfg, Config: c.BlackFriday}
+	ctx := &RenderingContext{Cfg: c.Cfg, Config: c.BlackFriday}
 	ctx.Content = []byte("testContent")
 	actualRenderedMarkdown := c.mmarkRender(ctx)
 	expectedRenderedMarkdown := []byte("<p>testContent</p>\n")
diff --git a/helpers/general.go b/helpers/general.go
index 00caf1ecc..962b35bc6 100644
--- a/helpers/general.go
+++ b/helpers/general.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.
@@ -92,7 +92,7 @@ func GuessType(in string) string {
 		return "org"
 	}
 
-	return "unknown"
+	return ""
 }
 
 // FirstUpper returns a string with the first character as upper case.
@@ -325,12 +325,15 @@ func InitLoggers() {
 // The idea is two remove an item in two Hugo releases to give users and theme authors
 // plenty of time to fix their templates.
 func Deprecated(object, item, alternative string, err bool) {
+	if !strings.HasSuffix(alternative, ".") {
+		alternative += "."
+	}
+
 	if err {
 		DistinctErrorLog.Printf("%s's %s is deprecated and will be removed in Hugo %s. %s", object, item, hugo.CurrentVersion.Next().ReleaseVersion(), alternative)
 
 	} else {
-		// Make sure the users see this while avoiding build breakage. This will not lead to an os.Exit(-1)
-		DistinctFeedbackLog.Printf("WARNING: %s's %s is deprecated and will be removed in a future release. %s", object, item, alternative)
+		DistinctWarnLog.Printf("%s's %s is deprecated and will be removed in a future release. %s", object, item, alternative)
 	}
 }
 
diff --git a/helpers/general_test.go b/helpers/general_test.go
index 1279df439..ed4c3d2c2 100644
--- a/helpers/general_test.go
+++ b/helpers/general_test.go
@@ -1,4 +1,4 @@
-// Copyright 2018 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.
@@ -42,7 +42,7 @@ func TestGuessType(t *testing.T) {
 		{"html", "html"},
 		{"htm", "html"},
 		{"org", "org"},
-		{"excel", "unknown"},
+		{"excel", ""},
 	} {
 		result := GuessType(this.in)
 		if result != this.expect {
@@ -166,6 +166,27 @@ var containsAdditionalTestData = []struct {
 	{"", []byte(""), false},
 }
 
+func TestSliceToLower(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		value    []string
+		expected []string
+	}{
+		{[]string{"a", "b", "c"}, []string{"a", "b", "c"}},
+		{[]string{"a", "B", "c"}, []string{"a", "b", "c"}},
+		{[]string{"A", "B", "C"}, []string{"a", "b", "c"}},
+	}
+
+	for _, test := range tests {
+		res := SliceToLower(test.value)
+		for i, val := range res {
+			if val != test.expected[i] {
+				t.Errorf("Case mismatch. Expected %s, got %s", test.expected[i], res[i])
+			}
+		}
+	}
+}
+
 func TestReaderContains(t *testing.T) {
 	for i, this := range append(containsBenchTestData, containsAdditionalTestData...) {
 		result := ReaderContains(strings.NewReader(this.v1), this.v2)
diff --git a/helpers/path.go b/helpers/path.go
index bf7e3bf99..de2c9b0a0 100644
--- a/helpers/path.go
+++ b/helpers/path.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.
@@ -86,6 +86,13 @@ func (p *PathSpec) MakePath(s string) string {
 	return p.UnicodeSanitize(s)
 }
 
+// MakePathsSanitized applies MakePathSanitized on every item in the slice
+func (p *PathSpec) MakePathsSanitized(paths []string) {
+	for i, path := range paths {
+		paths[i] = p.MakePathSanitized(path)
+	}
+}
+
 // MakePathSanitized creates a Unicode-sanitized string, with the spaces replaced
 func (p *PathSpec) MakePathSanitized(s string) string {
 	if p.DisablePathToLower {
diff --git a/helpers/pygments.go b/helpers/pygments.go
index 4a90e353d..64c5b3ea8 100644
--- a/helpers/pygments.go
+++ b/helpers/pygments.go
@@ -1,4 +1,4 @@
-// Copyright 2016 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.
@@ -56,7 +56,7 @@ type highlighters struct {
 }
 
 func newHiglighters(cs *ContentSpec) highlighters {
-	return highlighters{cs: cs, ignoreCache: cs.cfg.GetBool("ignoreCache"), cacheDir: cs.cfg.GetString("cacheDir")}
+	return highlighters{cs: cs, ignoreCache: cs.Cfg.GetBool("ignoreCache"), cacheDir: cs.Cfg.GetString("cacheDir")}
 }
 
 func (h highlighters) chromaHighlight(code, lang, optsStr string) (string, error) {