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, 13 insertions, 6 deletions

diff --git a/resources/testhelpers_test.go b/resources/testhelpers_test.go
index d0fcb59e7..200a795e3 100644
--- a/resources/testhelpers_test.go
+++ b/resources/testhelpers_test.go
@@ -9,7 +9,6 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
-	"path"
 	"runtime"
 	"strings"
 
@@ -18,6 +17,7 @@ import (
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/output"
+	"github.com/gohugoio/hugo/resources/page"
 	"github.com/gohugoio/hugo/resources/resource"
 	"github.com/spf13/afero"
 	"github.com/spf13/viper"
@@ -61,11 +61,20 @@ func newTestResourceSpecForBaseURL(assert *require.Assertions, baseURL string) *
 	return spec
 }
 
+func newTargetPaths(link string) func() page.TargetPaths {
+	return func() page.TargetPaths {
+		return page.TargetPaths{
+			SubResourceBaseTarget: filepath.FromSlash(link),
+			SubResourceBaseLink:   link,
+		}
+	}
+}
+
 func newTestResourceOsFs(assert *require.Assertions) *Spec {
 	cfg := viper.New()
 	cfg.Set("baseURL", "https://example.com")
 
-	workDir, err := ioutil.TempDir("", "hugores")
+	workDir, _ := ioutil.TempDir("", "hugores")
 
 	if runtime.GOOS == "darwin" && !strings.HasPrefix(workDir, "/private") {
 		// To get the entry folder in line with the rest. This its a little bit
@@ -124,11 +133,9 @@ func fetchResourceForSpec(spec *Spec, assert *require.Assertions, name string) r
 	src.Close()
 	assert.NoError(err)
 
-	factory := func(s string) string {
-		return path.Join("/a", s)
-	}
+	factory := newTargetPaths("/a")
 
-	r, err := spec.New(ResourceSourceDescriptor{TargetPathBuilder: factory, SourceFilename: name})
+	r, err := spec.New(ResourceSourceDescriptor{TargetPaths: factory, SourceFilename: name})
 	assert.NoError(err)
 
 	return r.(resource.ContentResource)