Added strike support to markdown (#1563)

This PR adds support for the strike operator in [both forms][1].

It does not include actual styling for the strike operator as it
makes the ~ character really hard to read.

[1]: https://webapps.stackexchange.com/questions/14986/strikethrough-with-github-markdown/103691#103691

components/prism-markdown.js

@@ -83,6 +83,7 @@ Prism.languages.insertBefore('markdown', 'prolog', {
 		// Allow only one line break
 		pattern: /(^|[^\\])(\*\*|__)(?:(?:\r?\n|\r)(?!\r?\n|\r)|.)+?\2/,
 		lookbehind: true,
+		greedy: true,
 		inside: {
 			'punctuation': /^\*\*|^__|\*\*$|__$/
 		}
@@ -94,10 +95,23 @@ Prism.languages.insertBefore('markdown', 'prolog', {
 		// Allow only one line break
 		pattern: /(^|[^\\])([*_])(?:(?:\r?\n|\r)(?!\r?\n|\r)|.)+?\2/,
 		lookbehind: true,
+		greedy: true,
 		inside: {
 			'punctuation': /^[*_]|[*_]$/
 		}
 	},
+	'strike': {
+		// ~~strike through~~
+		// ~strike~
+
+		// Allow only one line break
+		pattern: /(^|[^\\])(~~?)(?:(?:\r?\n|\r)(?!\r?\n|\r)|.)+?\2/,
+		lookbehind: true,
+		greedy: true,
+		inside: {
+			'punctuation': /^~~?|~~?$/
+		}
+	},
 	'url': {
 		// [example](http://example.com "Optional title")
 		// [example] [id]
@@ -116,5 +130,10 @@ Prism.languages.insertBefore('markdown', 'prolog', {
 
 Prism.languages.markdown['bold'].inside['url'] = Prism.languages.markdown['url'];
 Prism.languages.markdown['italic'].inside['url'] = Prism.languages.markdown['url'];
+Prism.languages.markdown['strike'].inside['url'] = Prism.languages.markdown['url'];
 Prism.languages.markdown['bold'].inside['italic'] = Prism.languages.markdown['italic'];
-Prism.languages.markdown['italic'].inside['bold'] = Prism.languages.markdown['bold'];
+Prism.languages.markdown['bold'].inside['strike'] = Prism.languages.markdown['strike'];
+Prism.languages.markdown['italic'].inside['bold'] = Prism.languages.markdown['bold'];
+Prism.languages.markdown['italic'].inside['strike'] = Prism.languages.markdown['strike'];
+Prism.languages.markdown['strike'].inside['bold'] = Prism.languages.markdown['bold'];
+Prism.languages.markdown['strike'].inside['italic'] = Prism.languages.markdown['italic'];

tests/languages/markdown/bold_feature.test

@@ -7,6 +7,7 @@ bar__
 
 __foo*bar*baz__
 __foo_bar_baz__
+__foo~bar~baz__
 __foo[bar](baz)__
 
 ----------------------------------------------------
@@ -55,6 +56,17 @@ __foo[bar](baz)__
 		"baz",
 		["punctuation", "__"]
 	]],
+	["bold", [
+		["punctuation", "__"],
+		"foo",
+		["strike", [
+			["punctuation", "~"],
+			"bar",
+			["punctuation", "~"]
+		]],
+		"baz",
+		["punctuation", "__"]
+	]],
 	["bold", [
 		["punctuation", "__"],
 		"foo",
@@ -67,4 +79,4 @@ __foo[bar](baz)__
 
 ----------------------------------------------------
 
-Checks for bold. Also tests for inclusion of italic and url.
+Checks for bold. Also tests for inclusion of italic, strike, and url.

tests/languages/markdown/strike_feature.test

@@ -0,0 +1,70 @@
+~~foobar~~
+~~foo
+bar~~
+~foobar~
+~foo
+bar~
+
+~foo*bar*baz~
+~foo__bar__baz~
+~foo[bar](baz)~
+
+----------------------------------------------------
+
+[
+	["strike", [
+		["punctuation", "~~"],
+		"foobar",
+		["punctuation", "~~"]
+	]],
+	["strike", [
+		["punctuation", "~~"],
+		"foo\r\nbar",
+		["punctuation", "~~"]
+	]],
+	["strike", [
+		["punctuation", "~"],
+		"foobar",
+		["punctuation", "~"]
+	]],
+	["strike", [
+		["punctuation", "~"],
+		"foo\r\nbar",
+		["punctuation", "~"]
+	]],
+
+	["strike", [
+		["punctuation", "~"],
+		"foo",
+		["italic", [
+			["punctuation", "*"],
+			"bar",
+			["punctuation", "*"]
+		]],
+		"baz",
+		["punctuation", "~"]
+	]],
+	["strike", [
+		["punctuation", "~"],
+		"foo",
+		["bold", [
+			["punctuation", "__"],
+			"bar",
+			["punctuation", "__"]
+		]],
+		"baz",
+		["punctuation", "~"]
+	]],
+	["strike", [
+		["punctuation", "~"],
+		"foo",
+		["url", [
+			"[bar](baz)"
+		]],
+		["punctuation", "~"]
+	]]
+]
+
+----------------------------------------------------
+
+Checks for strike. Also tests for inclusion of bold, italic, and url.