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, 10 insertions, 10 deletions

diff --git a/resources/image_cache.go b/resources/image_cache.go
index 58be839b3..cf1e999ba 100644
--- a/resources/image_cache.go
+++ b/resources/image_cache.go
@@ -14,13 +14,11 @@
 package resources
 
 import (
-	"fmt"
 	"image"
 	"io"
 	"path/filepath"
 	"strings"
 	"sync"
-	"time"
 
 	"github.com/gohugoio/hugo/common/hugio"
 
@@ -99,6 +97,11 @@ func (c *imageCache) getOrCreate(
 			return err
 		}
 
+		if w == nil {
+			// Nothing to write.
+			return nil
+		}
+
 		defer w.Close()
 		_, err = io.Copy(w, r)
 		return err
@@ -121,10 +124,12 @@ func (c *imageCache) getOrCreate(
 			return err
 		}
 
-		mw := hugio.NewMultiWriteCloser(w, destinations)
-		defer mw.Close()
+		if destinations != nil {
+			w = hugio.NewMultiWriteCloser(w, destinations)
+		}
+		defer w.Close()
 
-		return img.encodeTo(conf, conv, mw)
+		return img.encodeTo(conf, conv, w)
 	}
 
 	// Now look in the file cache.
@@ -157,8 +162,3 @@ func (c *imageCache) getOrCreate(
 func newImageCache(fileCache *filecache.Cache, ps *helpers.PathSpec) *imageCache {
 	return &imageCache{fileCache: fileCache, pathSpec: ps, store: make(map[string]*Image)}
 }
-
-func timeTrack(start time.Time, name string) {
-	elapsed := time.Since(start)
-	fmt.Printf("%s took %s\n", name, elapsed)
-}