Rewrite reference processing code in preparation for opening/closing from comment references (#8261)

* Add a markdown stripper for mentions and xrefs

* Improve comments

* Small code simplification

* Move reference code to modules/references

* Fix typo

* Make MarkdownStripper return [][]byte

* Implement preliminary keywords parsing

* Add FIXME comment

* Fix comment

* make fmt

* Fix permissions check

* Fix text assumptions

* Fix imports

* Fix lint, fmt

* Fix unused import

* Add missing export comment

* Bypass revive on implemented interface

* Move mdstripper into its own package

* Support alphanumeric patterns

* Refactor FindAllMentions

* Move mentions test to references

* Parse mentions from reference package

* Refactor code to implement renderizable references

* Fix typo

* Move patterns and tests to the references package

* Fix nil reference

* Preliminary rendering attempt of closing keywords

* Normalize names, comments, general tidy-up

* Add CSS style for action keywords

* Fix permission for admin and owner

* Fix golangci-lint

* Fix golangci-lint

2 files changed, 331 insertions, 0 deletions

diff --git a/modules/markup/mdstripper/mdstripper.go b/modules/markup/mdstripper/mdstripper.go
new file mode 100644
index 0000000000..7a901b17a9
--- /dev/null
+++ b/modules/markup/mdstripper/mdstripper.go
@@ -0,0 +1,260 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package mdstripper
+
+import (
+	"bytes"
+
+	"github.com/russross/blackfriday"
+)
+
+// MarkdownStripper extends blackfriday.Renderer
+type MarkdownStripper struct {
+	blackfriday.Renderer
+	links     []string
+	coallesce bool
+}
+
+const (
+	blackfridayExtensions = 0 |
+		blackfriday.EXTENSION_NO_INTRA_EMPHASIS |
+		blackfriday.EXTENSION_TABLES |
+		blackfriday.EXTENSION_FENCED_CODE |
+		blackfriday.EXTENSION_STRIKETHROUGH |
+		blackfriday.EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK |
+		blackfriday.EXTENSION_DEFINITION_LISTS |
+		blackfriday.EXTENSION_FOOTNOTES |
+		blackfriday.EXTENSION_HEADER_IDS |
+		blackfriday.EXTENSION_AUTO_HEADER_IDS |
+		// Not included in modules/markup/markdown/markdown.go;
+		// required here to process inline links
+		blackfriday.EXTENSION_AUTOLINK
+)
+
+//revive:disable:var-naming Implementing the Rendering interface requires breaking some linting rules
+
+// StripMarkdown parses markdown content by removing all markup and code blocks
+//	in order to extract links and other references
+func StripMarkdown(rawBytes []byte) (string, []string) {
+	stripper := &MarkdownStripper{
+		links: make([]string, 0, 10),
+	}
+	body := blackfriday.Markdown(rawBytes, stripper, blackfridayExtensions)
+	return string(body), stripper.GetLinks()
+}
+
+// StripMarkdownBytes parses markdown content by removing all markup and code blocks
+//	in order to extract links and other references
+func StripMarkdownBytes(rawBytes []byte) ([]byte, []string) {
+	stripper := &MarkdownStripper{
+		links: make([]string, 0, 10),
+	}
+	body := blackfriday.Markdown(rawBytes, stripper, blackfridayExtensions)
+	return body, stripper.GetLinks()
+}
+
+// block-level callbacks
+
+// BlockCode dummy function to proceed with rendering
+func (r *MarkdownStripper) BlockCode(out *bytes.Buffer, text []byte, infoString string) {
+	// Not rendered
+	r.coallesce = false
+}
+
+// BlockQuote dummy function to proceed with rendering
+func (r *MarkdownStripper) BlockQuote(out *bytes.Buffer, text []byte) {
+	// FIXME: perhaps it's better to leave out block quote for this?
+	r.processString(out, text, false)
+}
+
+// BlockHtml dummy function to proceed with rendering
+func (r *MarkdownStripper) BlockHtml(out *bytes.Buffer, text []byte) { //nolint
+	// Not rendered
+	r.coallesce = false
+}
+
+// Header dummy function to proceed with rendering
+func (r *MarkdownStripper) Header(out *bytes.Buffer, text func() bool, level int, id string) {
+	text()
+	r.coallesce = false
+}
+
+// HRule dummy function to proceed with rendering
+func (r *MarkdownStripper) HRule(out *bytes.Buffer) {
+	// Not rendered
+	r.coallesce = false
+}
+
+// List dummy function to proceed with rendering
+func (r *MarkdownStripper) List(out *bytes.Buffer, text func() bool, flags int) {
+	text()
+	r.coallesce = false
+}
+
+// ListItem dummy function to proceed with rendering
+func (r *MarkdownStripper) ListItem(out *bytes.Buffer, text []byte, flags int) {
+	r.processString(out, text, false)
+}
+
+// Paragraph dummy function to proceed with rendering
+func (r *MarkdownStripper) Paragraph(out *bytes.Buffer, text func() bool) {
+	text()
+	r.coallesce = false
+}
+
+// Table dummy function to proceed with rendering
+func (r *MarkdownStripper) Table(out *bytes.Buffer, header []byte, body []byte, columnData []int) {
+	r.processString(out, header, false)
+	r.processString(out, body, false)
+}
+
+// TableRow dummy function to proceed with rendering
+func (r *MarkdownStripper) TableRow(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, false)
+}
+
+// TableHeaderCell dummy function to proceed with rendering
+func (r *MarkdownStripper) TableHeaderCell(out *bytes.Buffer, text []byte, flags int) {
+	r.processString(out, text, false)
+}
+
+// TableCell dummy function to proceed with rendering
+func (r *MarkdownStripper) TableCell(out *bytes.Buffer, text []byte, flags int) {
+	r.processString(out, text, false)
+}
+
+// Footnotes dummy function to proceed with rendering
+func (r *MarkdownStripper) Footnotes(out *bytes.Buffer, text func() bool) {
+	text()
+}
+
+// FootnoteItem dummy function to proceed with rendering
+func (r *MarkdownStripper) FootnoteItem(out *bytes.Buffer, name, text []byte, flags int) {
+	r.processString(out, text, false)
+}
+
+// TitleBlock dummy function to proceed with rendering
+func (r *MarkdownStripper) TitleBlock(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, false)
+}
+
+// Span-level callbacks
+
+// AutoLink dummy function to proceed with rendering
+func (r *MarkdownStripper) AutoLink(out *bytes.Buffer, link []byte, kind int) {
+	r.processLink(out, link, []byte{})
+}
+
+// CodeSpan dummy function to proceed with rendering
+func (r *MarkdownStripper) CodeSpan(out *bytes.Buffer, text []byte) {
+	// Not rendered
+	r.coallesce = false
+}
+
+// DoubleEmphasis dummy function to proceed with rendering
+func (r *MarkdownStripper) DoubleEmphasis(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, false)
+}
+
+// Emphasis dummy function to proceed with rendering
+func (r *MarkdownStripper) Emphasis(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, false)
+}
+
+// Image dummy function to proceed with rendering
+func (r *MarkdownStripper) Image(out *bytes.Buffer, link []byte, title []byte, alt []byte) {
+	// Not rendered
+	r.coallesce = false
+}
+
+// LineBreak dummy function to proceed with rendering
+func (r *MarkdownStripper) LineBreak(out *bytes.Buffer) {
+	// Not rendered
+	r.coallesce = false
+}
+
+// Link dummy function to proceed with rendering
+func (r *MarkdownStripper) Link(out *bytes.Buffer, link []byte, title []byte, content []byte) {
+	r.processLink(out, link, content)
+}
+
+// RawHtmlTag dummy function to proceed with rendering
+func (r *MarkdownStripper) RawHtmlTag(out *bytes.Buffer, tag []byte) { //nolint
+	// Not rendered
+	r.coallesce = false
+}
+
+// TripleEmphasis dummy function to proceed with rendering
+func (r *MarkdownStripper) TripleEmphasis(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, false)
+}
+
+// StrikeThrough dummy function to proceed with rendering
+func (r *MarkdownStripper) StrikeThrough(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, false)
+}
+
+// FootnoteRef dummy function to proceed with rendering
+func (r *MarkdownStripper) FootnoteRef(out *bytes.Buffer, ref []byte, id int) {
+	// Not rendered
+	r.coallesce = false
+}
+
+// Low-level callbacks
+
+// Entity dummy function to proceed with rendering
+func (r *MarkdownStripper) Entity(out *bytes.Buffer, entity []byte) {
+	// FIXME: literal entities are not parsed; perhaps they should
+	r.coallesce = false
+}
+
+// NormalText dummy function to proceed with rendering
+func (r *MarkdownStripper) NormalText(out *bytes.Buffer, text []byte) {
+	r.processString(out, text, true)
+}
+
+// Header and footer
+
+// DocumentHeader dummy function to proceed with rendering
+func (r *MarkdownStripper) DocumentHeader(out *bytes.Buffer) {
+	r.coallesce = false
+}
+
+// DocumentFooter dummy function to proceed with rendering
+func (r *MarkdownStripper) DocumentFooter(out *bytes.Buffer) {
+	r.coallesce = false
+}
+
+// GetFlags returns rendering flags
+func (r *MarkdownStripper) GetFlags() int {
+	return 0
+}
+
+//revive:enable:var-naming
+
+func doubleSpace(out *bytes.Buffer) {
+	if out.Len() > 0 {
+		out.WriteByte('\n')
+	}
+}
+
+func (r *MarkdownStripper) processString(out *bytes.Buffer, text []byte, coallesce bool) {
+	// Always break-up words
+	if !coallesce || !r.coallesce {
+		doubleSpace(out)
+	}
+	out.Write(text)
+	r.coallesce = coallesce
+}
+func (r *MarkdownStripper) processLink(out *bytes.Buffer, link []byte, content []byte) {
+	// Links are processed out of band
+	r.links = append(r.links, string(link))
+	r.coallesce = false
+}
+
+// GetLinks returns the list of link data collected while parsing
+func (r *MarkdownStripper) GetLinks() []string {
+	return r.links
+}
diff --git a/modules/markup/mdstripper/mdstripper_test.go b/modules/markup/mdstripper/mdstripper_test.go
new file mode 100644
index 0000000000..157fe1975b
--- /dev/null
+++ b/modules/markup/mdstripper/mdstripper_test.go
@@ -0,0 +1,71 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package mdstripper
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMarkdownStripper(t *testing.T) {
+	type testItem struct {
+		markdown      string
+		expectedText  []string
+		expectedLinks []string
+	}
+
+	list := []testItem{
+		{
+			`
+## This is a title
+
+This is [one](link) to paradise.
+This **is emphasized**.
+This: should coallesce.
+
+` + "```" + `
+This is a code block.
+This should not appear in the output at all.
+` + "```" + `
+
+* Bullet 1
+* Bullet 2
+
+A HIDDEN ` + "`" + `GHOST` + "`" + ` IN THIS LINE.
+		`,
+			[]string{
+				"This is a title",
+				"This is",
+				"to paradise.",
+				"This",
+				"is emphasized",
+				".",
+				"This: should coallesce.",
+				"Bullet 1",
+				"Bullet 2",
+				"A HIDDEN",
+				"IN THIS LINE.",
+			},
+			[]string{
+				"link",
+			}},
+	}
+
+	for _, test := range list {
+		text, links := StripMarkdown([]byte(test.markdown))
+		rawlines := strings.Split(text, "\n")
+		lines := make([]string, 0, len(rawlines))
+		for _, line := range rawlines {
+			line := strings.TrimSpace(line)
+			if line != "" {
+				lines = append(lines, line)
+			}
+		}
+		assert.EqualValues(t, test.expectedText, lines)
+		assert.EqualValues(t, test.expectedLinks, links)
+	}
+}