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cloudhead
2010-03-12 15:03:05 -05:00
parent 7e2217ba86
commit e0623094fa
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lib/less/parser.js
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@@ -5,40 +5,40 @@ if (typeof(window) === 'undefined') {
//
// less.js - parser
//
// A relatively straight-forward recursive-descent parser.
// There is no tokenization/lexing stage, the input is parsed
// in one sweep.
// A relatively straight-forward recursive-descent parser.
// There is no tokenization/lexing stage, the input is parsed
// in one sweep.
//
// To make the parser fast enough to run in the browser, several
// optimization had to be made:
// To make the parser fast enough to run in the browser, several
// optimization had to be made:
//
// - Instead of the more commonly used technique of slicing the
// input string on every match, we use global regexps (/g),
// and move the `lastIndex` pointer on match, foregoing `slice()`
// completely. This gives us a 3x speed-up.
// - Instead of the more commonly used technique of slicing the
// input string on every match, we use global regexps (/g),
// and move the `lastIndex` pointer on match, foregoing `slice()`
// completely. This gives us a 3x speed-up.
//
// - Matching on a huge input is often cause of slowdowns,
// especially with the /g flag. The solution to that is to
// chunkify the input: we split it by /\n\n/, just to be on
// the safe side. The chunks are stored in the `chunks` var,
// `j` holds the current chunk index, and `current` holds
// the index of the current chunk in relation to `input`.
// This gives us an almost 4x speed-up.
// - Matching on a huge input is often cause of slowdowns,
// especially with the /g flag. The solution to that is to
// chunkify the input: we split it by /\n\n/, just to be on
// the safe side. The chunks are stored in the `chunks` var,
// `j` holds the current chunk index, and `current` holds
// the index of the current chunk in relation to `input`.
// This gives us an almost 4x speed-up.
//
// - In many cases, we don't need to match individual tokens;
// for example, if a value doesn't hold any variables, operations
// or dynamic references, the parser can effectively 'skip' it,
// treating it as a literal.
// An example would be '1px solid #000' - which evaluates to itself,
// we don't need to know what the individual components are.
// The drawback, of course is that you don't get the benefits of
// syntax-checking on the CSS. This gives us a 50% speed-up in the parser,
// and a smaller speed-up in the code-gen.
// - In many cases, we don't need to match individual tokens;
// for example, if a value doesn't hold any variables, operations
// or dynamic references, the parser can effectively 'skip' it,
// treating it as a literal.
// An example would be '1px solid #000' - which evaluates to itself,
// we don't need to know what the individual components are.
// The drawback, of course is that you don't get the benefits of
// syntax-checking on the CSS. This gives us a 50% speed-up in the parser,
// and a smaller speed-up in the code-gen.
//
//
// Token matching is done with the `$` function, which either takes
// a terminal string or regexp, or a non-terminal function to call.
// It also takes care of moving all the indices forwards.
// Token matching is done with the `$` function, which either takes
// a terminal string or regexp, or a non-terminal function to call.
// It also takes care of moving all the indices forwards.
//
//
var input, // LeSS input string
@@ -48,21 +48,6 @@ var input, // LeSS input string
current, // index of current chunk, in `input`
inputLength;
function peek(tok) {
var match;
if (typeof(tok) === 'string') {
return input[i] === tok;
} else {
tok.lastIndex = i;
if ((match = tok.exec(input)) &&
(tok.lastIndex - match[0].length === i)) {
return match;
}
}
}
//
// Parse from a token, regexp or string, and move forward if match
//
@@ -124,8 +109,34 @@ function $(tok) {
}
}
// Same as $(), but don't change the state of the parser,
// just return the match.
function peek(tok) {
var match;
if (typeof(tok) === 'string') {
return input[i] === tok;
} else {
tok.lastIndex = i;
if ((match = tok.exec(input)) &&
(tok.lastIndex - match[0].length === i)) {
return match;
}
}
}
//
// The Parser
//
less.parser = {
// The optimization level dictates the thoroughness of the parser,
// the lower the number, the less nodes it will create in the tree.
// This could matter for debugging, or if you want to access
// the individual nodes in the tree.
optimization: 2,
//
// Parse an input string into an abstract syntax tree
//
@@ -161,13 +172,21 @@ less.parser = {
chunks = [input];
}
// Start with the primary rule
// Start with the primary rule.
// The whole syntax tree is held under a Ruleset node,
// with the `root` property set to true, so no `{}` are
// output.
root = new(tree.Ruleset)([], $(this.parsers.primary));
root.root = true;
// If `i` is smaller than the input length - 1,
// If `i` is smaller than the `input.length - 1`,
// it means the parser wasn't able to parse the whole
// string, so we've got a parsing error.
//
// We try to extract a \n delimited string,
// showing the line where the parse error occured.
// We split it up into two parts (the part which parsed,
// and the part which didn't), so we can color them differently.
if (i < input.length - 1) {
start = (function () {
for (var n = i; n > 0; n--) {
@@ -185,7 +204,52 @@ less.parser = {
}
return root;
},
//
// Here in, the parsing rules/functions
//
// The basic structure of the syntax tree generated is as follows:
//
// Ruleset -> Rule -> Value -> Expression -> Entity
//
// Here's some LESS code:
//
// .class {
// color: #fff;
// border: 1px solid #000;
// width: @w + 4px;
// > .child {...}
// }
//
// And here's what the parse tree might look like:
//
// Ruleset (Selector '.class', [
// Rule ("color", Value ([Expression [Color #fff]]))
// Rule ("border", Value ([Expression [Dimension 1px][Keyword "solid"][Color #000]]))
// Rule ("width", Value ([Expression [Operation "+" [Variable "@w"][Dimension 4px]]]))
// Ruleset (Selector [Element '>', '.child'], [...])
// ])
//
// In general, most rules will try to parse a token with the `$()` function, and if the return
// value is truly, will return a new node, of the relevant type. Sometimes, we need to check
// first, before parsing, that's when we use `peek()`.
//
parsers: {
//
// The `primary` rule is the *entry* and *exit* point of the parser.
// The rules here can appear at any level of the parse tree.
//
// The recursive nature of the grammar is an interplay between the `block`
// rule, which represents `{ ... }`, the `ruleset` rule, and this `primary` rule,
// as represented by this simplified grammar:
//
// primary → (ruleset | rule)+
// ruleset → selector+ block
// block → '{' primary '}'
//
// Only at one point is the primary rule not called from the
// block rule: at the root level.
//
primary: function () {
var node, root = [];
@@ -196,6 +260,10 @@ less.parser = {
}
return root;
},
// We create a Comment node for CSS comments `/* */`,
// but keep the LeSS comments `//` silent, by just skipping
// over them.
comment: function () {
var comment;
@@ -207,7 +275,16 @@ less.parser = {
return $(/\/\/.*/g);
}
},
//
// Entities are tokens which can be found inside an Expression
//
entities: {
//
// A string, which supports escaping " and '
//
// "milky way" 'he\'s the one!'
//
quoted: function () {
var str;
if (input[i] !== '"' && input[i] !== "'") return;
@@ -216,10 +293,27 @@ less.parser = {
return new(tree.Quoted)(str[0], str[1] || str[2]);
}
},
//
// A catch-all word, such as:
//
// black border-collapse
//
keyword: function () {
var k;
if (k = $(/[A-Za-z-]+/g)) { return new(tree.Keyword)(k) }
},
//
// A function call
//
// rgb(255, 0, 255)
//
// We also try to catch IE's `alpha()`, but let the `alpha` parser
// deal with the details.
//
// The arguments are parsed with the `entities.arguments` parser.
//
call: function () {
var name, args;
@@ -242,13 +336,19 @@ less.parser = {
}
return args;
},
accessor: function () {
},
literal: function () {
return $(this.entities.dimension) ||
$(this.entities.color) ||
$(this.entities.quoted);
},
//
// Parse url() tokens
//
// We use a specific rule for urls, because they don't really behave like
// standard function calls. The difference is that the argument doesn't have
// to be enclosed within a string, so it can't be parsed as an Expression.
//
url: function () {
var value;
@@ -258,6 +358,15 @@ less.parser = {
return new(tree.URL)(value);
},
//
// A Variable entity, such as `@fink`, in
//
// width: @fink + 2px
//
// We use a different parser for variable definitions,
// see `parsers.variable`.
//
variable: function () {
var name;
@@ -265,6 +374,14 @@ less.parser = {
return new(tree.Variable)(name);
}
},
//
// A Hexadecimal color
//
// #4F3C2F
//
// `rgb` and `hsl` colors are parsed through the `entities.call` parser.
//
color: function () {
var rgb;
@@ -272,6 +389,12 @@ less.parser = {
return new(tree.Color)(rgb[1]);
}
},
//
// A Dimension, that is, a number and a unit
//
// 0.5em 95%
//
dimension: function () {
var value, c = input.charCodeAt(i);
if ((c > 57 || c < 45) || c === 47) return;
@@ -281,11 +404,25 @@ less.parser = {
}
}
},
//
// The variable part of a variable definition. Used in the `rule` parser
//
// @fink:
//
variable: function () {
var name;
if (input[i] === '@' && (name = $(/(@[a-zA-Z0-9_-]+)\s*:/g))) { return name[1] }
},
//
// A font size/line-height shorthand
//
// small/12px
//
// We need to peek first, or we'll match on keywords and dimensions
//
shorthand: function () {
var a, b;
@@ -339,12 +476,21 @@ less.parser = {
}
}
},
entity: function () {
var e;
if (e = $(this.entities.literal) || $(this.entities.variable) || $(this.entities.url) ||
$(this.entities.call) || $(this.entities.keyword)) { return e }
//
// Entities are the smallest recognized token,
// and can be found inside a rule's value.
//
entity: function () {
return $(this.entities.literal) || $(this.entities.variable) || $(this.entities.url) ||
$(this.entities.call) || $(this.entities.keyword);
},
//
// A Rule terminator. Note that we use `peek()` to check for '}',
// because the `block` rule will be expecting it, but we still need to make sure
// it's there, if ';' was ommitted.
//
end: function () {
return $(';') || peek('}');
},
@@ -406,6 +552,10 @@ less.parser = {
return content;
}
},
//
// div, .class, body > p {...}
//
ruleset: function () {
var selectors = [], s, rules, match;