/usr/share/javascript/prettify/lang-swift.js is in libjs-prettify 2015.12.04+dfsg-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | var a=null;
PR.registerLangHandler(PR.createSimpleLexer([["pln",/^[ \n\r\t\v\f\0]+/,a," \n\r\t\v\f\x00"],["str",/^"(?:[^"\\]|(?:\\.)|(?:\\\((?:[^"\\)]|\\.)*\)))*"/,a,'"']],[["lit",/^(?:(?:0x[\da-fA-F][\da-fA-F_]*\.[\da-fA-F][\da-fA-F_]*[pP]?)|(?:\d[\d_]*\.\d[\d_]*[eE]?))[+-]?\d[\d_]*/,a],["lit",/^-?(?:(?:0(?:(?:b[01][01_]*)|(?:o[0-7][0-7_]*)|(?:x[\da-fA-F][\da-fA-F_]*)))|(?:\d[\d_]*))/,a],["lit",/^(?:true|false|nil)\b/,a],["kwd",/^\b(?:__COLUMN__|__FILE__|__FUNCTION__|__LINE__|#available|#else|#elseif|#endif|#if|#line|arch|arm|arm64|associativity|as|break|case|catch|class|continue|convenience|default|defer|deinit|didSet|do|dynamic|dynamicType|else|enum|fallthrough|final|for|func|get|import|indirect|infix|init|inout|internal|i386|if|in|iOS|iOSApplicationExtension|is|lazy|left|let|mutating|none|nonmutating|operator|optional|OSX|OSXApplicationExtension|override|postfix|precedence|prefix|private|protocol|Protocol|public|required|rethrows|return|right|safe|self|set|static|struct|subscript|super|switch|throw|try|Type|typealias|unowned|unsafe|var|weak|watchOS|while|willSet|x86_64)\b/,a],
["com",/^\/\/.*?[\n\r]/,a],["com",/^\/\*[\s\S]*?(?:\*\/|$)/,a],["pun",/^<<=|<=|<<|>>=|>=|>>|===|==|\.\.\.|&&=|\.\.<|!==|!=|&=|~=|~|\(|\)|\[|\]|{|}|@|#|;|\.|,|:|\|\|=|\?\?|\|\||&&|&\*|&\+|&-|&=|\+=|-=|\/=|\*=|\^=|%=|\|=|->|`|==|\+\+|--|\/|\+|!|\*|%|<|>|&|\||\^|\?|=|-|_/,a],["typ",/^\b(?:[@_]?[A-Z]+[a-z][A-Za-z_$@0-9]*|\w+_t\b)/,a]]),["swift"]);
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