Add Markdown diagrams and render hooks for code blocks

You can now create custom hook templates for code blocks, either one for all (`render-codeblock.html`) or for a given code language (e.g. `render-codeblock-go.html`).

We also used this new hook to add support for diagrams in Hugo:

* Goat (Go ASCII Tool) is built-in and enabled by default; just create a fenced code block with the language `goat` and start draw your Ascii diagrams.
* Another popular alternative for diagrams in Markdown, Mermaid (supported by GitHub), can also be implemented with a simple template. See the Hugo documentation for more information.

Updates #7765
Closes #9538
Fixes #9553
Fixes #8520
Fixes #6702
Fixes #9558

3 files changed, 42 insertions, 94 deletions

diff --git a/tpl/os/init_test.go b/tpl/os/init_test.go
deleted file mode 100644
index 5d756bab2..000000000
--- a/tpl/os/init_test.go
+++ /dev/null
@@ -1,42 +0,0 @@
-// Copyright 2017 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 os
-
-import (
-	"testing"
-
-	qt "github.com/frankban/quicktest"
-	"github.com/gohugoio/hugo/deps"
-	"github.com/gohugoio/hugo/htesting/hqt"
-	"github.com/gohugoio/hugo/tpl/internal"
-)
-
-func TestInit(t *testing.T) {
-	c := qt.New(t)
-	var found bool
-	var ns *internal.TemplateFuncsNamespace
-
-	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
-		ns = nsf(&deps.Deps{})
-		if ns.Name == name {
-			found = true
-			break
-		}
-	}
-
-	c.Assert(found, qt.Equals, true)
-	ctx, err := ns.Context()
-	c.Assert(err, qt.IsNil)
-	c.Assert(ctx, hqt.IsSameType, &Namespace{})
-}
diff --git a/tpl/os/os.go b/tpl/os/os.go
index 43c42f5e1..8b195a527 100644
--- a/tpl/os/os.go
+++ b/tpl/os/os.go
@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	_os "os"
+	"path/filepath"
 
 	"github.com/gohugoio/hugo/deps"
 	"github.com/spf13/afero"
@@ -27,17 +28,9 @@ import (
 
 // New returns a new instance of the os-namespaced template functions.
 func New(d *deps.Deps) *Namespace {
-	var rfs afero.Fs
-	if d.Fs != nil {
-		rfs = d.Fs.WorkingDir
-		if d.PathSpec != nil && d.PathSpec.BaseFs != nil {
-			rfs = afero.NewReadOnlyFs(afero.NewCopyOnWriteFs(d.PathSpec.BaseFs.Content.Fs, d.Fs.WorkingDir))
-		}
-
-	}
-
 	return &Namespace{
-		readFileFs: rfs,
+		readFileFs: afero.NewReadOnlyFs(afero.NewCopyOnWriteFs(d.PathSpec.BaseFs.Content.Fs, d.PathSpec.BaseFs.Work)),
+		workFs:     d.PathSpec.BaseFs.Work,
 		deps:       d,
 	}
 }
@@ -45,6 +38,7 @@ func New(d *deps.Deps) *Namespace {
 // Namespace provides template functions for the "os" namespace.
 type Namespace struct {
 	readFileFs afero.Fs
+	workFs     afero.Fs
 	deps       *deps.Deps
 }
 
@@ -66,8 +60,9 @@ func (ns *Namespace) Getenv(key interface{}) (string, error) {
 // readFile reads the file named by filename in the given filesystem
 // and returns the contents as a string.
 func readFile(fs afero.Fs, filename string) (string, error) {
-	if filename == "" {
-		return "", errors.New("readFile needs a filename")
+	filename = filepath.Clean(filename)
+	if filename == "" || filename == "." || filename == string(_os.PathSeparator) {
+		return "", errors.New("invalid filename")
 	}
 
 	b, err := afero.ReadFile(fs, filename)
@@ -101,7 +96,7 @@ func (ns *Namespace) ReadDir(i interface{}) ([]_os.FileInfo, error) {
 		return nil, err
 	}
 
-	list, err := afero.ReadDir(ns.deps.Fs.WorkingDir, path)
+	list, err := afero.ReadDir(ns.workFs, path)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read directory %q: %s", path, err)
 	}
diff --git a/tpl/os/os_test.go b/tpl/os/os_test.go
index bbc0d018c..59491e97c 100644
--- a/tpl/os/os_test.go
+++ b/tpl/os/os_test.go
@@ -11,34 +11,26 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package os
+package os_test
 
 import (
 	"path/filepath"
 	"testing"
 
-	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/hugolib"
+	"github.com/gohugoio/hugo/tpl/os"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/gohugoio/hugo/deps"
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/spf13/afero"
 )
 
 func TestReadFile(t *testing.T) {
 	t.Parallel()
-	c := qt.New(t)
-
-	workingDir := "/home/hugo"
 
-	v := config.New()
-	v.Set("workingDir", workingDir)
+	b := newFileTestBuilder(t).Build()
 
-	// f := newTestFuncsterWithViper(v)
-	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
+	// helpers.PrintFs(b.H.PathSpec.BaseFs.Work, "", _os.Stdout)
 
-	afero.WriteFile(ns.deps.Fs.Source, filepath.Join(workingDir, "/f/f1.txt"), []byte("f1-content"), 0755)
-	afero.WriteFile(ns.deps.Fs.Source, filepath.Join("/home", "f2.txt"), []byte("f2-content"), 0755)
+	ns := os.New(b.H.Deps)
 
 	for _, test := range []struct {
 		filename string
@@ -53,13 +45,13 @@ func TestReadFile(t *testing.T) {
 
 		result, err := ns.ReadFile(test.filename)
 
-		if b, ok := test.expect.(bool); ok && !b {
-			c.Assert(err, qt.Not(qt.IsNil))
+		if bb, ok := test.expect.(bool); ok && !bb {
+			b.Assert(err, qt.Not(qt.IsNil))
 			continue
 		}
 
-		c.Assert(err, qt.IsNil)
-		c.Assert(result, qt.Equals, test.expect)
+		b.Assert(err, qt.IsNil)
+		b.Assert(result, qt.Equals, test.expect)
 	}
 }
 
@@ -67,15 +59,8 @@ func TestFileExists(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	workingDir := "/home/hugo"
-
-	v := config.New()
-	v.Set("workingDir", workingDir)
-
-	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
-
-	afero.WriteFile(ns.deps.Fs.Source, filepath.Join(workingDir, "/f/f1.txt"), []byte("f1-content"), 0755)
-	afero.WriteFile(ns.deps.Fs.Source, filepath.Join("/home", "f2.txt"), []byte("f2-content"), 0755)
+	b := newFileTestBuilder(t).Build()
+	ns := os.New(b.H.Deps)
 
 	for _, test := range []struct {
 		filename string
@@ -101,15 +86,8 @@ func TestFileExists(t *testing.T) {
 
 func TestStat(t *testing.T) {
 	t.Parallel()
-	c := qt.New(t)
-	workingDir := "/home/hugo"
-
-	v := config.New()
-	v.Set("workingDir", workingDir)
-
-	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
-
-	afero.WriteFile(ns.deps.Fs.Source, filepath.Join(workingDir, "/f/f1.txt"), []byte("f1-content"), 0755)
+	b := newFileTestBuilder(t).Build()
+	ns := os.New(b.H.Deps)
 
 	for _, test := range []struct {
 		filename string
@@ -123,11 +101,28 @@ func TestStat(t *testing.T) {
 		result, err := ns.Stat(test.filename)
 
 		if test.expect == nil {
-			c.Assert(err, qt.Not(qt.IsNil))
+			b.Assert(err, qt.Not(qt.IsNil))
 			continue
 		}
 
-		c.Assert(err, qt.IsNil)
-		c.Assert(result.Size(), qt.Equals, test.expect)
+		b.Assert(err, qt.IsNil)
+		b.Assert(result.Size(), qt.Equals, test.expect)
 	}
 }
+
+func newFileTestBuilder(t *testing.T) *hugolib.IntegrationTestBuilder {
+	files := `
+-- f/f1.txt --
+f1-content
+-- home/f2.txt --
+f2-content
+	`
+
+	return hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:           t,
+			TxtarString: files,
+			WorkingDir:  "/mywork",
+		},
+	)
+}