Add Goldmark as the new default markdown handler

This commit adds the fast and CommonMark compliant Goldmark as the new default markdown handler in Hugo.

If you want to continue using BlackFriday as the default for md/markdown extensions, you can use this configuration:

```toml
[markup]
defaultMarkdownHandler="blackfriday"
```

Fixes #5963
Fixes #1778
Fixes #6355

4 files changed, 92 insertions, 57 deletions

diff --git a/markup/blackfriday/blackfriday_config/config.go b/markup/blackfriday/blackfriday_config/config.go
new file mode 100644
index 000000000..f26f7c570
--- /dev/null
+++ b/markup/blackfriday/blackfriday_config/config.go
@@ -0,0 +1,70 @@
+// 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.
+// 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 helpers implements general utility functions that work with
+// and on content.  The helper functions defined here lay down the
+// foundation of how Hugo works with files and filepaths, and perform
+// string operations on content.
+
+package blackfriday_config
+
+import (
+	"github.com/mitchellh/mapstructure"
+	"github.com/pkg/errors"
+)
+
+// Default holds the default BlackFriday config.
+// Do not change!
+var Default = Config{
+	Smartypants:           true,
+	AngledQuotes:          false,
+	SmartypantsQuotesNBSP: false,
+	Fractions:             true,
+	HrefTargetBlank:       false,
+	NofollowLinks:         false,
+	NoreferrerLinks:       false,
+	SmartDashes:           true,
+	LatexDashes:           true,
+	PlainIDAnchors:        true,
+	TaskLists:             true,
+	SkipHTML:              false,
+}
+
+// Config holds configuration values for BlackFriday rendering.
+// It is kept here because it's used in several packages.
+type Config struct {
+	Smartypants           bool
+	SmartypantsQuotesNBSP bool
+	AngledQuotes          bool
+	Fractions             bool
+	HrefTargetBlank       bool
+	NofollowLinks         bool
+	NoreferrerLinks       bool
+	SmartDashes           bool
+	LatexDashes           bool
+	TaskLists             bool
+	PlainIDAnchors        bool
+	Extensions            []string
+	ExtensionsMask        []string
+	SkipHTML              bool
+
+	FootnoteAnchorPrefix       string
+	FootnoteReturnLinkContents string
+}
+
+func UpdateConfig(b Config, m map[string]interface{}) (Config, error) {
+	if err := mapstructure.Decode(m, &b); err != nil {
+		return b, errors.WithMessage(err, "failed to decode rendering config")
+	}
+	return b, nil
+}
diff --git a/markup/blackfriday/convert.go b/markup/blackfriday/convert.go
index f9d957a4e..350defcb6 100644
--- a/markup/blackfriday/convert.go
+++ b/markup/blackfriday/convert.go
@@ -15,36 +15,27 @@
 package blackfriday
 
 import (
+	"github.com/gohugoio/hugo/markup/blackfriday/blackfriday_config"
 	"github.com/gohugoio/hugo/markup/converter"
-	"github.com/gohugoio/hugo/markup/internal"
 	"github.com/russross/blackfriday"
 )
 
 // Provider is the package entry point.
-var Provider converter.NewProvider = provider{}
+var Provider converter.ProviderProvider = provider{}
 
 type provider struct {
 }
 
 func (p provider) New(cfg converter.ProviderConfig) (converter.Provider, error) {
-	defaultBlackFriday, err := internal.NewBlackfriday(cfg)
-	if err != nil {
-		return nil, err
-	}
-
-	defaultExtensions := getMarkdownExtensions(defaultBlackFriday)
-
-	pygmentsCodeFences := cfg.Cfg.GetBool("pygmentsCodeFences")
-	pygmentsCodeFencesGuessSyntax := cfg.Cfg.GetBool("pygmentsCodeFencesGuessSyntax")
-	pygmentsOptions := cfg.Cfg.GetString("pygmentsOptions")
+	defaultExtensions := getMarkdownExtensions(cfg.MarkupConfig.BlackFriday)
 
-	var n converter.NewConverter = func(ctx converter.DocumentContext) (converter.Converter, error) {
-		b := defaultBlackFriday
+	return converter.NewProvider("blackfriday", func(ctx converter.DocumentContext) (converter.Converter, error) {
+		b := cfg.MarkupConfig.BlackFriday
 		extensions := defaultExtensions
 
 		if ctx.ConfigOverrides != nil {
 			var err error
-			b, err = internal.UpdateBlackFriday(b, ctx.ConfigOverrides)
+			b, err = blackfriday_config.UpdateConfig(b, ctx.ConfigOverrides)
 			if err != nil {
 				return nil, err
 			}
@@ -56,27 +47,16 @@ func (p provider) New(cfg converter.ProviderConfig) (converter.Provider, error)
 			bf:         b,
 			extensions: extensions,
 			cfg:        cfg,
-
-			pygmentsCodeFences:            pygmentsCodeFences,
-			pygmentsCodeFencesGuessSyntax: pygmentsCodeFencesGuessSyntax,
-			pygmentsOptions:               pygmentsOptions,
 		}, nil
-	}
-
-	return n, nil
+	}), nil
 
 }
 
 type blackfridayConverter struct {
 	ctx        converter.DocumentContext
-	bf         *internal.BlackFriday
+	bf         blackfriday_config.Config
 	extensions int
-
-	pygmentsCodeFences            bool
-	pygmentsCodeFencesGuessSyntax bool
-	pygmentsOptions               string
-
-	cfg converter.ProviderConfig
+	cfg        converter.ProviderConfig
 }
 
 func (c *blackfridayConverter) AnchorSuffix() string {
@@ -90,7 +70,6 @@ func (c *blackfridayConverter) Convert(ctx converter.RenderContext) (converter.R
 	r := c.getHTMLRenderer(ctx.RenderTOC)
 
 	return converter.Bytes(blackfriday.Markdown(ctx.Src, r, c.extensions)), nil
-
 }
 
 func (c *blackfridayConverter) getHTMLRenderer(renderTOC bool) blackfriday.Renderer {
@@ -114,7 +93,7 @@ func (c *blackfridayConverter) getHTMLRenderer(renderTOC bool) blackfriday.Rende
 	}
 }
 
-func getFlags(renderTOC bool, cfg *internal.BlackFriday) int {
+func getFlags(renderTOC bool, cfg blackfriday_config.Config) int {
 
 	var flags int
 
@@ -168,7 +147,7 @@ func getFlags(renderTOC bool, cfg *internal.BlackFriday) int {
 	return flags
 }
 
-func getMarkdownExtensions(cfg *internal.BlackFriday) int {
+func getMarkdownExtensions(cfg blackfriday_config.Config) int {
 	// Default Blackfriday common extensions
 	commonExtensions := 0 |
 		blackfriday.EXTENSION_NO_INTRA_EMPHASIS |
diff --git a/markup/blackfriday/convert_test.go b/markup/blackfriday/convert_test.go
index 094edf35f..b4d66dec6 100644
--- a/markup/blackfriday/convert_test.go
+++ b/markup/blackfriday/convert_test.go
@@ -18,19 +18,15 @@ import (
 
 	"github.com/spf13/viper"
 
-	"github.com/gohugoio/hugo/markup/internal"
-
 	"github.com/gohugoio/hugo/markup/converter"
 
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/markup/blackfriday/blackfriday_config"
 	"github.com/russross/blackfriday"
 )
 
 func TestGetMarkdownExtensionsMasksAreRemovedFromExtensions(t *testing.T) {
-	c := qt.New(t)
-	b, err := internal.NewBlackfriday(converter.ProviderConfig{Cfg: viper.New()})
-	c.Assert(err, qt.IsNil)
-
+	b := blackfriday_config.Default
 	b.Extensions = []string{"headerId"}
 	b.ExtensionsMask = []string{"noIntraEmphasis"}
 
@@ -45,9 +41,7 @@ func TestGetMarkdownExtensionsByDefaultAllExtensionsAreEnabled(t *testing.T) {
 		testFlag int
 	}
 
-	c := qt.New(t)
-	b, err := internal.NewBlackfriday(converter.ProviderConfig{Cfg: viper.New()})
-	c.Assert(err, qt.IsNil)
+	b := blackfriday_config.Default
 
 	b.Extensions = []string{""}
 	b.ExtensionsMask = []string{""}
@@ -79,9 +73,7 @@ func TestGetMarkdownExtensionsByDefaultAllExtensionsAreEnabled(t *testing.T) {
 }
 
 func TestGetMarkdownExtensionsAddingFlagsThroughRenderingContext(t *testing.T) {
-	c := qt.New(t)
-	b, err := internal.NewBlackfriday(converter.ProviderConfig{Cfg: viper.New()})
-	c.Assert(err, qt.IsNil)
+	b := blackfriday_config.Default
 
 	b.Extensions = []string{"definitionLists"}
 	b.ExtensionsMask = []string{""}
@@ -93,10 +85,7 @@ func TestGetMarkdownExtensionsAddingFlagsThroughRenderingContext(t *testing.T) {
 }
 
 func TestGetFlags(t *testing.T) {
-	c := qt.New(t)
-	cfg := converter.ProviderConfig{Cfg: viper.New()}
-	b, err := internal.NewBlackfriday(cfg)
-	c.Assert(err, qt.IsNil)
+	b := blackfriday_config.Default
 	flags := getFlags(false, b)
 	if flags&blackfriday.HTML_USE_XHTML != blackfriday.HTML_USE_XHTML {
 		t.Errorf("Test flag: %d was not found amongs set flags:%d; Result: %d", blackfriday.HTML_USE_XHTML, flags, flags&blackfriday.HTML_USE_XHTML)
@@ -105,9 +94,8 @@ func TestGetFlags(t *testing.T) {
 
 func TestGetAllFlags(t *testing.T) {
 	c := qt.New(t)
-	cfg := converter.ProviderConfig{Cfg: viper.New()}
-	b, err := internal.NewBlackfriday(cfg)
-	c.Assert(err, qt.IsNil)
+
+	b := blackfriday_config.Default
 
 	type data struct {
 		testFlag int
@@ -145,9 +133,8 @@ func TestGetAllFlags(t *testing.T) {
 	for _, d := range allFlags {
 		expectedFlags |= d.testFlag
 	}
-	if expectedFlags != actualFlags {
-		t.Errorf("Expected flags (%d) did not equal actual (%d) flags.", expectedFlags, actualFlags)
-	}
+
+	c.Assert(actualFlags, qt.Equals, expectedFlags)
 }
 
 func TestConvert(t *testing.T) {
diff --git a/markup/blackfriday/renderer.go b/markup/blackfriday/renderer.go
index 9f4d44e02..a46e46b55 100644
--- a/markup/blackfriday/renderer.go
+++ b/markup/blackfriday/renderer.go
@@ -30,10 +30,9 @@ type hugoHTMLRenderer struct {
 // BlockCode renders a given text as a block of code.
 // Pygments is used if it is setup to handle code fences.
 func (r *hugoHTMLRenderer) BlockCode(out *bytes.Buffer, text []byte, lang string) {
-	if r.c.pygmentsCodeFences && (lang != "" || r.c.pygmentsCodeFencesGuessSyntax) {
-		opts := r.c.pygmentsOptions
+	if r.c.cfg.MarkupConfig.Highlight.CodeFences {
 		str := strings.Trim(string(text), "\n\r")
-		highlighted, _ := r.c.cfg.Highlight(str, lang, opts)
+		highlighted, _ := r.c.cfg.Highlight(str, lang, "")
 		out.WriteString(highlighted)
 	} else {
 		r.Renderer.BlockCode(out, text, lang)