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

common/collections/append.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.
@@ -92,9 +92,7 @@ func appendToInterfaceSlice(tov reflect.Value, from ...interface{}) ([]interface
 		tos = append(tos, tov.Index(i).Interface())
 	}
 
-	for _, v := range from {
-		tos = append(tos, v)
-	}
+	tos = append(tos, from...)
 
 	return tos, nil
 }

common/collections/slice_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.
@@ -75,11 +75,11 @@ func (p *tstSlicerIn2) Slice(in interface{}) (interface{}, error) {
 }
 
 func (p *tstSlicerIn1) Name() string {
-	return p.Name()
+	return p.name
 }
 
 func (p *tstSlicerIn2) Name() string {
-	return p.Name()
+	return p.name
 }
 
 func (p *tstSlicer) Slice(in interface{}) (interface{}, error) {

common/hugio/readers.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.
@@ -32,6 +32,7 @@ type ReadSeekCloser interface {
 }
 
 // ReadSeekerNoOpCloser implements ReadSeekCloser by doing nothing in Close.
+// TODO(bep) rename this and simila to ReadSeekerNopCloser, naming used in stdlib, which kind of makes sense.
 type ReadSeekerNoOpCloser struct {
 	ReadSeeker
 }

common/hugo/site.go

@@ -1,24 +0,0 @@
-// Copyright 2018 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 hugo
-
-import "github.com/gohugoio/hugo/langs"
-
-// Site represents a site in the build. This is currently a very narrow interface,
-// but the actual implementation will be richer, see hugolib.SiteInfo.
-type Site interface {
-	Language() *langs.Language
-	IsServer() bool
-	Hugo() Info
-}

common/maps/scratch.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.
@@ -28,6 +28,24 @@ type Scratch struct {
 	mu     sync.RWMutex
 }
 
+// Scratcher provides a scratching service.
+type Scratcher interface {
+	Scratch() *Scratch
+}
+
+type scratcher struct {
+	s *Scratch
+}
+
+func (s scratcher) Scratch() *Scratch {
+	return s.s
+}
+
+// NewScratcher creates a new Scratcher.
+func NewScratcher() Scratcher {
+	return scratcher{s: NewScratch()}
+}
+
 // Add will, for single values, add (using the + operator) the addend to the existing addend (if found).
 // Supports numeric values and strings.
 //

common/types/types.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.
@@ -16,6 +16,7 @@ package types
 
 import (
 	"fmt"
+	"reflect"
 
 	"github.com/spf13/cast"
 )
@@ -56,3 +57,24 @@ func NewKeyValuesStrings(key string, values ...string) KeyValues {
 type Zeroer interface {
 	IsZero() bool
 }
+
+// IsNil reports whether v is nil.
+func IsNil(v interface{}) bool {
+	if v == nil {
+		return true
+	}
+
+	value := reflect.ValueOf(v)
+	switch value.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
+		return value.IsNil()
+	}
+
+	return false
+}
+
+// DevMarker is a marker interface for types that should only be used during
+// development.
+type DevMarker interface {
+	DevOnly()
+}