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css.js
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css.js
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import XRegExp from "xregexp";
import { Lexer, CstParser, createToken as orgCreateToken } from "chevrotain";
// ----------------- lexer -----------------
// Based on the specs in:
// https://www.w3.org/TR/CSS21/grammar.html
// A little mini DSL for easier lexer definition using xRegExp.
const fragments = {};
function FRAGMENT(name, def) {
fragments[name] = XRegExp.build(def, fragments);
}
function MAKE_PATTERN(def, flags) {
return XRegExp.build(def, fragments, flags);
}
// ----------------- Lexer -----------------
// A Little wrapper to save us the trouble of manually building the
// array of cssTokens
const cssTokens = [];
const createToken = function () {
const newToken = orgCreateToken.apply(null, arguments);
cssTokens.push(newToken);
return newToken;
};
// The order of fragments definitions is important
FRAGMENT("nl", "\\n|\\r|\\f");
FRAGMENT("h", "[0-9a-f]");
FRAGMENT("nonascii", "[\\u0240-\\uffff]");
FRAGMENT("unicode", "{{h}}{1,6}");
FRAGMENT("escape", "{{unicode}}|\\\\[^\\r\\n\\f0-9a-f]");
FRAGMENT("nmstart", "[_a-zA-Z]|{{nonascii}}|{{escape}}");
FRAGMENT("nmchar", "[_a-zA-Z0-9-]|{{nonascii}}|{{escape}}");
FRAGMENT("string1", '\\"([^\\n\\r\\f\\"]|{{nl}}|{{escape}})*\\"');
FRAGMENT("string2", "\\'([^\\n\\r\\f\\']|{{nl}}|{{escape}})*\\'");
FRAGMENT("comment", "\\/\\*[^*]*\\*+([^/*][^*]*\\*+)*\\/");
FRAGMENT("name", "({{nmchar}})+");
FRAGMENT("url", "([!#\\$%&*-~]|{{nonascii}}|{{escape}})*");
FRAGMENT("spaces", "[ \\t\\r\\n\\f]+");
FRAGMENT("ident", "-?{{nmstart}}{{nmchar}}*");
FRAGMENT("num", "[0-9]+|[0-9]*\\.[0-9]+");
/* eslint-disable no-unused-vars -- tokens are collected in our `createToken` wrapper */
const Whitespace = createToken({
name: "Whitespace",
pattern: MAKE_PATTERN("{{spaces}}"),
// The W3C specs are are defined in a whitespace sensitive manner.
// But there is only **one** place where the grammar is truly whitespace sensitive.
// So the whitespace sensitivity was implemented via a GATE in the selector rule.
group: Lexer.SKIPPED,
});
const Comment = createToken({
name: "Comment",
pattern: /\/\*[^*]*\*+([^/*][^*]*\*+})*\//,
group: Lexer.SKIPPED,
// note that comments could span multiple lines.
// forgetting to enable this flag will cause inaccuracies in the lexer location tracking.
line_breaks: true,
});
// This group has to be defined BEFORE Ident as their prefix is a valid Ident
const Uri = createToken({ name: "Uri", pattern: Lexer.NA });
const UriString = createToken({
name: "UriString",
pattern: MAKE_PATTERN(
"url\\((:?{{spaces}})?({{string1}}|{{string2}})(:?{{spaces}})?\\)",
),
categories: Uri,
});
const UriUrl = createToken({
name: "UriUrl",
pattern: MAKE_PATTERN("url\\((:?{{spaces}})?{{url}}(:?{{spaces}})?\\)"),
categories: Uri,
});
const Func = createToken({
name: "Func",
pattern: MAKE_PATTERN("{{ident}}\\("),
});
const Cdo = createToken({ name: "Cdo", pattern: /<!--/ });
// Cdc must be before Minus
const Cdc = createToken({ name: "Cdc", pattern: /-->/ });
const Includes = createToken({ name: "Includes", pattern: /~=/ });
const Dasmatch = createToken({ name: "Dasmatch", pattern: /\|=/ });
const Exclamation = createToken({ name: "Exclamation", pattern: /!/ });
const Dot = createToken({ name: "Dot", pattern: /\./ });
const LCurly = createToken({ name: "LCurly", pattern: /{/ });
const RCurly = createToken({ name: "RCurly", pattern: /}/ });
const LSquare = createToken({ name: "LSquare", pattern: /\[/ });
const RSquare = createToken({ name: "RSquare", pattern: /]/ });
const LParen = createToken({ name: "LParen", pattern: /\(/ });
const RParen = createToken({ name: "RParen", pattern: /\)/ });
const Comma = createToken({ name: "Comma", pattern: /,/ });
const Colon = createToken({ name: "Colon", pattern: /:/ });
const SemiColon = createToken({ name: "SemiColon", pattern: /;/ });
const Equals = createToken({ name: "Equals", pattern: /=/ });
const Star = createToken({ name: "Star", pattern: /\*/ });
const Plus = createToken({ name: "Plus", pattern: /\+/ });
const GreaterThan = createToken({ name: "GreaterThan", pattern: />/ });
const Slash = createToken({ name: "Slash", pattern: /\// });
const StringLiteral = createToken({
name: "StringLiteral",
pattern: MAKE_PATTERN("{{string1}}|{{string2}}"),
});
const Hash = createToken({
name: "Hash",
pattern: MAKE_PATTERN("#{{name}}"),
});
// note that the spec defines import as : @{I}{M}{P}{O}{R}{T}
// Where every letter is defined in this pattern:
// i|\\0{0,4}(49|69)(\r\n|[ \t\r\n\f])?|\\i
// Lets count the number of ways to write the letter 'i'
// i // 2 options due to case insensitivity
// |
// \\0{0,4} // 5 options for number of spaces
// (49|69) // 2 options for asci value
// (\r\n|[ \t\r\n\f])? // 7 options, so the total for this alternative is 5 * 2 * 7 = 70 (!!!)
// |
// \\i // 1 option.
// so there are a total of 73 options to write the letter 'i'
// This gives us 73^6 options to write the word "import" which is a number with 12 digits...
// This implementation does not bother with this crap :) and instead settles for
// "just" 64 option to write "impPorT" (case due to case insensitivity)
const ImportSym = createToken({
name: "ImportSym",
pattern: /@import/i,
});
const PageSym = createToken({ name: "PageSym", pattern: /@page/i });
const MediaSym = createToken({ name: "MediaSym", pattern: /@media/i });
const CharsetSym = createToken({
name: "CharsetSym",
pattern: /@charset/i,
});
const ImportantSym = createToken({
name: "ImportantSym",
pattern: /important/i,
});
const Ems = createToken({
name: "Ems",
pattern: MAKE_PATTERN("{{num}}em", "i"),
});
const Exs = createToken({
name: "Exs",
pattern: MAKE_PATTERN("{{num}}ex", "i"),
});
const Length = createToken({ name: "Length", pattern: Lexer.NA });
const Px = createToken({
name: "Px",
pattern: MAKE_PATTERN("{{num}}px", "i"),
categories: Length,
});
const Cm = createToken({
name: "Cm",
pattern: MAKE_PATTERN("{{num}}cm", "i"),
categories: Length,
});
const Mm = createToken({
name: "Mm",
pattern: MAKE_PATTERN("{{num}}mm", "i"),
categories: Length,
});
const In = createToken({
name: "In",
pattern: MAKE_PATTERN("{{num}}in", "i"),
categories: Length,
});
const Pt = createToken({
name: "Pt",
pattern: MAKE_PATTERN("{{num}}pt", "i"),
categories: Length,
});
const Pc = createToken({
name: "Pc",
pattern: MAKE_PATTERN("{{num}}pc", "i"),
categories: Length,
});
const Angle = createToken({ name: "Angle", pattern: Lexer.NA });
const Deg = createToken({
name: "Deg",
pattern: MAKE_PATTERN("{{num}}deg", "i"),
categories: Angle,
});
const Rad = createToken({
name: "Rad",
pattern: MAKE_PATTERN("{{num}}rad", "i"),
categories: Angle,
});
const Grad = createToken({
name: "Grad",
pattern: MAKE_PATTERN("{{num}}grad", "i"),
categories: Angle,
});
const Time = createToken({ name: "Time", pattern: Lexer.NA });
const Ms = createToken({
name: "Ms",
pattern: MAKE_PATTERN("{{num}}ms", "i"),
categories: Time,
});
const Sec = createToken({
name: "Sec",
pattern: MAKE_PATTERN("{{num}}sec", "i"),
categories: Time,
});
const Freq = createToken({ name: "Freq", pattern: Lexer.NA });
const Hz = createToken({
name: "Hz",
pattern: MAKE_PATTERN("{{num}}hz", "i"),
categories: Freq,
});
const Khz = createToken({
name: "Khz",
pattern: MAKE_PATTERN("{{num}}khz", "i"),
categories: Freq,
});
const Percentage = createToken({
name: "Percentage",
pattern: MAKE_PATTERN("{{num}}%", "i"),
});
// Num must appear after all the num forms with a suffix
const Num = createToken({
name: "Num",
pattern: MAKE_PATTERN("{{num}}"),
});
// Ident must be before Minus
const Ident = createToken({
name: "Ident",
pattern: MAKE_PATTERN("{{ident}}"),
});
const Minus = createToken({ name: "Minus", pattern: /-/ });
/* eslint-enable no-unused-vars -- tokens are collected in our `createToken` wrapper */
const CssLexer = new Lexer(cssTokens);
// ----------------- parser -----------------
class CssParser extends CstParser {
// Unfortunately no support for class fields with initializer in ES2015, only in esNext...
// so the parsing rules are defined inside the constructor, as each parsing rule must be initialized by
// invoking RULE(...)
// see: https://github.com/jeffmo/es-class-fields-and-static-properties
constructor() {
super(cssTokens);
const $ = this;
this.RULE("stylesheet", () => {
// [ CHARSET_SYM STRING ';' ]?
$.OPTION(() => {
$.SUBRULE($.charsetHeader);
});
// [S|CDO|CDC]*
$.SUBRULE($.cdcCdo);
// [ import [ CDO S* | CDC S* ]* ]*
$.MANY(() => {
$.SUBRULE($.cssImport);
$.SUBRULE2($.cdcCdo);
});
// [ [ ruleset | media | page ] [ CDO S* | CDC S* ]* ]*
$.MANY2(() => {
$.SUBRULE($.contents);
});
});
this.RULE("charsetHeader", () => {
$.CONSUME(CharsetSym);
$.CONSUME(StringLiteral);
$.CONSUME(SemiColon);
});
this.RULE("contents", () => {
$.OR([
{ ALT: () => $.SUBRULE($.ruleset) },
{ ALT: () => $.SUBRULE($.media) },
{ ALT: () => $.SUBRULE($.page) },
]);
$.SUBRULE3($.cdcCdo);
});
// factor out repeating pattern for cdc/cdo
this.RULE("cdcCdo", () => {
$.MANY(() => {
// prettier-ignore
$.OR([
{ ALT: () => $.CONSUME(Cdo) },
{ ALT: () => $.CONSUME(Cdc) }
])
});
});
// IMPORT_SYM S*
// [STRING|URI] S* media_list? ';' S*
this.RULE("cssImport", () => {
$.CONSUME(ImportSym);
$.OR([
{ ALT: () => $.CONSUME(StringLiteral) },
{ ALT: () => $.CONSUME(Uri) },
]);
$.OPTION(() => {
$.SUBRULE($.media_list);
});
$.CONSUME(SemiColon);
});
// MEDIA_SYM S* media_list '{' S* ruleset* '}' S*
this.RULE("media", () => {
$.CONSUME(MediaSym);
$.SUBRULE($.media_list);
$.CONSUME(LCurly);
$.SUBRULE($.ruleset);
$.CONSUME(RCurly);
});
// medium [ COMMA S* medium]*
this.RULE("media_list", () => {
$.SUBRULE($.medium);
$.MANY_SEP({
SEP: Comma,
DEF: () => {
$.SUBRULE2($.medium);
},
});
});
// IDENT S*
this.RULE("medium", () => {
$.CONSUME(Ident);
});
// PAGE_SYM S* pseudo_page?
// '{' S* declaration? [ ';' S* declaration? ]* '}' S*
this.RULE("page", () => {
$.CONSUME(PageSym);
$.OPTION(() => {
$.SUBRULE($.pseudo_page);
});
$.SUBRULE($.declarationsGroup);
});
// '{' S* declaration? [ ';' S* declaration? ]* '}' S*
// factored out repeating grammar pattern
this.RULE("declarationsGroup", () => {
$.CONSUME(LCurly);
$.OPTION(() => {
$.SUBRULE($.declaration);
});
$.MANY(() => {
$.CONSUME(SemiColon);
$.OPTION2(() => {
$.SUBRULE2($.declaration);
});
});
$.CONSUME(RCurly);
});
// ':' IDENT S*
this.RULE("pseudo_page", () => {
$.CONSUME(Colon);
$.CONSUME(Ident);
});
// '/' S* | ',' S*
this.RULE("operator", () => {
$.OR([{ ALT: () => $.CONSUME(Slash) }, { ALT: () => $.CONSUME(Comma) }]);
});
// '+' S* | '>' S*
this.RULE("combinator", () => {
$.OR([
{ ALT: () => $.CONSUME(Plus) },
{ ALT: () => $.CONSUME(GreaterThan) },
]);
});
// '-' | '+'
this.RULE("unary_operator", () => {
$.OR([{ ALT: () => $.CONSUME(Minus) }, { ALT: () => $.CONSUME(Plus) }]);
});
// IDENT S*
this.RULE("property", () => {
$.CONSUME(Ident);
});
// selector [ ',' S* selector ]*
// '{' S* declaration? [ ';' S* declaration? ]* '}' S*
this.RULE("ruleset", () => {
$.MANY_SEP({
SEP: Comma,
DEF: () => {
$.SUBRULE($.selector);
},
});
$.SUBRULE($.declarationsGroup);
});
// simple_selector [ combinator selector | S+ [ combinator? selector ]? ]?
this.RULE("selector", () => {
$.SUBRULE($.simple_selector);
$.OPTION(() => {
$.OR([
{
GATE: () => {
const prevToken = $.LA(0);
const nextToken = $.LA(1);
// This is the only place in CSS where the grammar is whitespace sensitive.
return nextToken.startOffset > prevToken.endOffset;
},
ALT: () => {
$.OPTION2(() => {
$.SUBRULE($.combinator);
});
$.SUBRULE($.selector);
},
},
{
ALT: () => {
$.SUBRULE2($.combinator);
$.SUBRULE2($.selector);
},
},
]);
});
});
// element_name [ HASH | class | attrib | pseudo ]*
// | [ HASH | class | attrib | pseudo ]+
this.RULE("simple_selector", () => {
$.OR([
{
ALT: () => {
$.SUBRULE($.element_name);
$.MANY(() => {
$.SUBRULE($.simple_selector_suffix);
});
},
},
{
ALT: () => {
$.AT_LEAST_ONE(() => {
$.SUBRULE2($.simple_selector_suffix);
});
},
},
]);
});
// helper grammar rule to avoid repetition
// [ HASH | class | attrib | pseudo ]+
this.RULE("simple_selector_suffix", () => {
$.OR([
{ ALT: () => $.CONSUME(Hash) },
{ ALT: () => $.SUBRULE($.class) },
{ ALT: () => $.SUBRULE($.attrib) },
{ ALT: () => $.SUBRULE($.pseudo) },
]);
});
// '.' IDENT
this.RULE("class", () => {
$.CONSUME(Dot);
$.CONSUME(Ident);
});
// IDENT | '*'
this.RULE("element_name", () => {
$.OR([{ ALT: () => $.CONSUME(Ident) }, { ALT: () => $.CONSUME(Star) }]);
});
// '[' S* IDENT S* [ [ '=' | INCLUDES | DASHMATCH ] S* [ IDENT | STRING ] S* ]? ']'
this.RULE("attrib", () => {
$.CONSUME(LSquare);
$.CONSUME(Ident);
this.OPTION(() => {
$.OR([
{ ALT: () => $.CONSUME(Equals) },
{ ALT: () => $.CONSUME(Includes) },
{ ALT: () => $.CONSUME(Dasmatch) },
]);
$.OR2([
{ ALT: () => $.CONSUME2(Ident) },
{ ALT: () => $.CONSUME(StringLiteral) },
]);
});
$.CONSUME(RSquare);
});
// ':' [ IDENT | FUNCTION S* [IDENT S*]? ')' ]
this.RULE("pseudo", () => {
$.CONSUME(Colon);
$.OR([
{ ALT: () => $.CONSUME(Ident) },
{
ALT: () => {
$.CONSUME(Func);
$.OPTION(() => {
$.CONSUME2(Ident);
});
$.CONSUME(RParen);
},
},
]);
});
// property ':' S* expr prio?
this.RULE("declaration", () => {
$.SUBRULE($.property);
$.CONSUME(Colon);
$.SUBRULE($.expr);
$.OPTION(() => {
$.SUBRULE($.prio);
});
});
// IMPORTANT_SYM S*
this.RULE("prio", () => {
$.CONSUME(ImportantSym);
});
// term [ operator? term ]*
this.RULE("expr", () => {
$.SUBRULE($.term);
$.MANY(() => {
$.OPTION(() => {
$.SUBRULE($.operator);
});
$.SUBRULE2($.term);
});
});
// unary_operator?
// [ NUMBER S* | PERCENTAGE S* | LENGTH S* | EMS S* | EXS S* | ANGLE S* |
// TIME S* | FREQ S* ]
// | STRING S* | IDENT S* | URI S* | hexcolor | function
this.RULE("term", () => {
$.OPTION(() => {
$.SUBRULE($.unary_operator);
});
$.OR([
{ ALT: () => $.CONSUME(Num) },
{ ALT: () => $.CONSUME(Percentage) },
{ ALT: () => $.CONSUME(Length) },
{ ALT: () => $.CONSUME(Ems) },
{ ALT: () => $.CONSUME(Exs) },
{ ALT: () => $.CONSUME(Angle) },
{ ALT: () => $.CONSUME(Time) },
{ ALT: () => $.CONSUME(Freq) },
{ ALT: () => $.CONSUME(StringLiteral) },
{ ALT: () => $.CONSUME(Ident) },
{ ALT: () => $.CONSUME(Uri) },
{ ALT: () => $.SUBRULE($.hexcolor) },
{ ALT: () => $.SUBRULE($.cssFunction) },
]);
});
// FUNCTION S* expr ')' S*
this.RULE("cssFunction", () => {
$.CONSUME(Func);
$.SUBRULE($.expr);
$.CONSUME(RParen);
});
this.RULE("hexcolor", () => {
$.CONSUME(Hash);
});
// very important to call this after all the rules have been setup.
// otherwise the parser may not work correctly as it will lack information
// derived from the self analysis.
this.performSelfAnalysis();
}
}
// ----------------- wrapping it all together -----------------
// reuse the same parser instance.
const parser = new CssParser();
export function parseCss(text) {
const lexResult = CssLexer.tokenize(text);
// setting a new input will RESET the parser instance's state.
parser.input = lexResult.tokens;
// any top level rule may be used as an entry point
const cst = parser.stylesheet();
return {
cst: cst,
lexErrors: lexResult.errors,
parseErrors: parser.errors,
};
}