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Use antlr v4 for syntax check

Can I use antlr v4 for syntax check before I actually run the code?

Example :
I defined syntax: select * from table, I want to know the statement is correct or not before actually executing it.

select * from table

Following is my code :

val listener = new SQLListener()
val loadLexer = new SQLLexer(new ANTLRInputStream(input))
val tokens = new CommonTokenStream(loadLexer)
val parser = new SQLParser(tokens)
val stat = parser.statement()


I tried but DefaultErrorStrategy won't throw an Exception

DefaultErrorStrategy

I tried this:

parser.addErrorListener(new BaseErrorListener {
override def syntaxError(recognizer: Recognizer[_, _ <: ATNSimulator],
offendingSymbol: scala.Any,
line: Int,
charPositionInLine: Int,
msg: String, e: RecognitionException ): Unit = {
println("==========2============"+msg)
throw new AssertionError("line: " + line + ", offset: " + charPositionInLine +
", symbol:" + offendingSymbol + " " + msg)
}
})


but get this:

Error: Note: the super classes of contain the following, non final members named syntaxError:

2 Answers
2

If the input contains any syntax errors, this will call the visitErrorNode method on the listener. So if you define that method in your listener, you'll see any errors that occur.

visitErrorNode

If your listener is directly executing the code (rather than first building an AST or other form of IR), you probably won't want your listener to even start executing when there's a syntax error. One way to achieve that would be to set the BailErrorStrategy instead of the DefaultErrorStrategy as the error handling strategy of your parser (using setErrorHandler on the parser). This will throw an exception as soon as a syntax error occurs.

setErrorHandler

If you don't want to abort on the first error and/or you want some additional checks beyond just syntax errors (like checking for certain types of semantic errors), an alternative is to have a listener just to perform those checks. Then you'd run your code-executing listener only if the error-checking listener does not find any errors.

You are on the right track here. Use your error listener to store the errors in a list while parsing. Afterwards you can then check that list.

That requires however not to do any action during the parsing process (e.g. in a parse listener) other than stuff related to the parsing process itself. Any follow up action (e.g. error markup in an editor) should be done after the parse run.

If you like to see an example of an application using this approach take a look at the parser module implementation of MySQL Workbench. It also demonstrates the 2-stage parsing strategy for quicker parsing.

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