Searching for a tool to validate a specific less file at the syntax level. The issue lies in the validator not recognizing dependencies or detecting declared mixins.
Many existing less processors do not work due to missing dependencies that cannot be provided during this stage of the process.
An npm package would be the ideal solution for my needs.
After much consideration, I finally opted to utilize antlr4
Here are the steps I followed:
The setup includes these commands:
$ cd /usr/local/lib
$ sudo curl -O http://www.antlr.org/download/antlr-4.5-complete.jar
$ export CLASSPATH=".:/usr/local/lib/antlr-4.5-complete.jar:$CLASSPATH"
$ alias antlr4='java -jar /usr/local/lib/antlr-4.5-complete.jar'
$ alias grun='java org.antlr.v4.runtime.misc.TestRig
This information is sourced directly from the webpage.
You can now obtain the grammar from https://github.com/antlr/grammars-v4
At this stage, you can generate the JavaScript version of your grammar
In my scenario, I established a directory, downloaded the files, and implemented all my tests within it:
antlr4 -Dlanguage=JavaScript LessParser.g4
antlr4 -Dlanguage=JavaScript LessLexer.g4
This process generates a JavaScript file that you will need, but the antlr library is required to use these files in your node program.
npm link antlr4
Now, the coding begins:
var antlr4 = require('antlr4/index');
var MyGrammarLexer = require('./LessLexer.js');
var MyGrammarParser = require('./LessParser.js');
var input = "html{ .hey(); color: @light-blue; background:#333}";
var chars = new antlr4.InputStream(input);
var lexer = new MyGrammarLexer.LessLexer(chars);
var tokens = new antlr4.CommonTokenStream(lexer);
var parser = new MyGrammarParser.LessParser(tokens);
parser.buildParseTrees = true;
var ErrorListener = antlr4.error.ErrorListener;
function CustomErrorListener() {
ErrorListener.call(this);
return this;
}
CustomErrorListener.prototype = Object.create(ErrorListener.prototype);
CustomErrorListener.prototype.constructor = CustomErrorListener;
CustomErrorListener.prototype.syntaxError = function(recognizer, offendingSymbol, line, column, msg, e) {
throw ('throw a simple exception');
};
parser.addErrorListener(new CustomErrorListener());
try{
var tree = parser.stylesheet();
} catch (e){
console.log('I catch you!!!')
}
The crucial elements in this code are the functions lessLexer, lessParser, and parser.stylesheet(); These differ for each grammar. The last one is where you specify the point in the grammar that needs validation. In my case, I utilized the file LessParser.g4, which outlines various nodes in the grammar definition:
parser grammar LessParser;
options { tokenVocab=LessLexer; }
stylesheet
: statement*
;
statement
: importDeclaration
| ruleset
| variableDeclaration ';'
| mixinDefinition
;
variableName
: AT variableName
| AT Identifier
;
commandStatement
: (expression+) mathStatement?
;
mathCharacter
: TIMES | PLUS | DIV | MINUS | PERC
;
With this information, you can validate strings like a stylesheet, statement, variableName...
Lastly, the Error Validation aspect is noteworthy, as I used it to halt validation at the first error encountered. While my implementation is basic, there is potential for further enhancements in this area
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