prism-cshtml.js

// Docs:
// https://docs.microsoft.com/en-us/aspnet/core/razor-pages/?view=aspnetcore-5.0&tabs=visual-studio
// https://docs.microsoft.com/en-us/aspnet/core/mvc/views/razor?view=aspnetcore-5.0

(function (Prism) {

	var commentLike = /\/(?![/*])|\/\/.*[\r\n]|\/\*[^*]*(?:\*(?!\/)[^*]*)*\*\//.source;
	var stringLike =
		/@(?!")|"(?:[^\r\n\\"]|\\.)*"|@"(?:[^\\"]|""|\\[\s\S])*"(?!")/.source +
		'|' +
		/'(?:(?:[^\r\n'\\]|\\.|\\[Uux][\da-fA-F]{1,8})'|(?=[^\\](?!')))/.source;

	/**
	 * Creates a nested pattern where all occurrences of the string `<<self>>` are replaced with the pattern itself.
	 *
	 * @param {string} pattern
	 * @param {number} depthLog2
	 * @returns {string}
	 */
	function nested(pattern, depthLog2) {
		for (var i = 0; i < depthLog2; i++) {
			pattern = pattern.replace(/<self>/g, function () { return '(?:' + pattern + ')'; });
		}
		return pattern
			.replace(/<self>/g, '[^\\s\\S]')
			.replace(/<str>/g, '(?:' + stringLike + ')')
			.replace(/<comment>/g, '(?:' + commentLike + ')');
	}

	var round = nested(/\((?:[^()'"@/]|<str>|<comment>|<self>)*\)/.source, 2);
	var square = nested(/\[(?:[^\[\]'"@/]|<str>|<comment>|<self>)*\]/.source, 2);
	var curly = nested(/\{(?:[^{}'"@/]|<str>|<comment>|<self>)*\}/.source, 2);
	var angle = nested(/<(?:[^<>'"@/]|<str>|<comment>|<self>)*>/.source, 2);

	// Note about the above bracket patterns:
	// They all ignore HTML expressions that might be in the C# code. This is a problem because HTML (like strings and
	// comments) is parsed differently. This is a huge problem because HTML might contain brackets and quotes which
	// messes up the bracket and string counting implemented by the above patterns.
	//
	// This problem is not fixable because 1) HTML expression are highly context sensitive and very difficult to detect
	// and 2) they require one capturing group at every nested level. See the `tagRegion` pattern to admire the
	// complexity of an HTML expression.
	//
	// To somewhat alleviate the problem a bit, the patterns for characters (e.g. 'a') is very permissive, it also
	// allows invalid characters to support HTML expressions like this: <p>That's it!</p>.

	var tagAttrs = /(?:\s(?:\s*[^\s>\/=]+(?:\s*=\s*(?:"[^"]*"|'[^']*'|[^\s'">=]+(?=[\s>]))|(?=[\s/>])))+)?/.source;
	var tagContent = /(?!\d)[^\s>\/=$<%]+/.source + tagAttrs + /\s*\/?>/.source;
	var tagRegion =
		/\B@?/.source +
		'(?:' +
		/<([a-zA-Z][\w:]*)/.source + tagAttrs + /\s*>/.source +
		'(?:' +
		(
			/[^<]/.source +
			'|' +
			// all tags that are not the start tag
			// eslint-disable-next-line regexp/strict
			/<\/?(?!\1\b)/.source + tagContent +
			'|' +
			// nested start tag
			nested(
				// eslint-disable-next-line regexp/strict
				/<\1/.source + tagAttrs + /\s*>/.source +
				'(?:' +
				(
					/[^<]/.source +
					'|' +
					// all tags that are not the start tag
					// eslint-disable-next-line regexp/strict
					/<\/?(?!\1\b)/.source + tagContent +
					'|' +
					'<self>'
				) +
				')*' +
				// eslint-disable-next-line regexp/strict
				/<\/\1\s*>/.source,
				2
			)
		) +
		')*' +
		// eslint-disable-next-line regexp/strict
		/<\/\1\s*>/.source +
		'|' +
		/</.source + tagContent +
		')';

	// Now for the actual language definition(s):
	//
	// Razor as a language has 2 parts:
	//  1) CSHTML: A markup-like language that has been extended with inline C# code expressions and blocks.
	//  2) C#+HTML: A variant of C# that can contain CSHTML tags as expressions.
	//
	// In the below code, both CSHTML and C#+HTML will be create as separate language definitions that reference each
	// other. However, only CSHTML will be exported via `Prism.languages`.

	Prism.languages.cshtml = Prism.languages.extend('markup', {});

	var csharpWithHtml = Prism.languages.insertBefore('csharp', 'string', {
		'html': {
			pattern: RegExp(tagRegion),
			greedy: true,
			inside: Prism.languages.cshtml
		},
	}, { csharp: Prism.languages.extend('csharp', {}) });

	var cs = {
		pattern: /\S[\s\S]*/,
		alias: 'language-csharp',
		inside: csharpWithHtml
	};

	Prism.languages.insertBefore('cshtml', 'prolog', {
		'razor-comment': {
			pattern: /@\*[\s\S]*?\*@/,
			greedy: true,
			alias: 'comment'
		},

		'block': {
			pattern: RegExp(
				/(^|[^@])@/.source +
				'(?:' +
				[
					// @{ ... }
					curly,
					// @code{ ... }
					/(?:code|functions)\s*/.source + curly,
					// @for (...) { ... }
					/(?:for|foreach|lock|switch|using|while)\s*/.source + round + /\s*/.source + curly,
					// @do { ... } while (...);
					/do\s*/.source + curly + /\s*while\s*/.source + round + /(?:\s*;)?/.source,
					// @try { ... } catch (...) { ... } finally { ... }
					/try\s*/.source + curly + /\s*catch\s*/.source + round + /\s*/.source + curly + /\s*finally\s*/.source + curly,
					// @if (...) {...} else if (...) {...} else {...}
					/if\s*/.source + round + /\s*/.source + curly + '(?:' + /\s*else/.source + '(?:' + /\s+if\s*/.source + round + ')?' + /\s*/.source + curly + ')*',
				].join('|') +
				')'
			),
			lookbehind: true,
			greedy: true,
			inside: {
				'keyword': /^@\w*/,
				'csharp': cs
			}
		},

		'directive': {
			pattern: /^([ \t]*)@(?:addTagHelper|attribute|implements|inherits|inject|layout|model|namespace|page|preservewhitespace|removeTagHelper|section|tagHelperPrefix|using)(?=\s).*/m,
			lookbehind: true,
			greedy: true,
			inside: {
				'keyword': /^@\w+/,
				'csharp': cs
			}
		},

		'value': {
			pattern: RegExp(
				/(^|[^@])@/.source +
				/(?:await\b\s*)?/.source +
				'(?:' + /\w+\b/.source + '|' + round + ')' +
				'(?:' + /[?!]?\.\w+\b/.source + '|' + round + '|' + square + '|' + angle + round + ')*'
			),
			lookbehind: true,
			greedy: true,
			alias: 'variable',
			inside: {
				'keyword': /^@/,
				'csharp': cs
			}
		},

		'delegate-operator': {
			pattern: /(^|[^@])@(?=<)/,
			lookbehind: true,
			alias: 'operator'
		}
	});

	Prism.languages.razor = Prism.languages.cshtml;

}(Prism));