ANTLR: How to skip multiline comments

问题:

Given the following lexer:

lexer grammar CodeTableLexer;

@header {
    package ch.bsource.ice.parsers;
}

CodeTabHeader   : OBracket Code ' ' Table ' ' Version CBracket;
CodeTable       : Code ' '* Table;
EndCodeTable    : 'end' ' '* Code ' '* Table;
Code            : 'code';
Table           : 'table';
Version         : '1.0';
Row             : 'row';
Tabdef          : 'tabdef';
Override        : 'override' | 'no_override';
Obsolete        : 'obsolete';
Substitute      : 'substitute';
Status          : 'activ' | 'inactive';
Pkg             : 'include_pkg' | 'exclude_pkg';
Ddic            : 'include_ddic' | 'exclude_ddic';
Tab             : 'tab';
Naming          : 'naming';
Dfltlang        : 'dfltlang';
Language        : 'english' | 'german' | 'french' | 'italian' | 'spanish';
Null            : 'null';
Comma           : ',';
OBracket        : '[';
CBracket        : ']';

Boolean
    : 'true' 
    | 'false'
    ;

Number
    : Int* ('.' Digit*)?
    ;

Identifier
    : ('a'..'z' | 'A'..'Z' | '_') ('a'..'z' | 'A'..'Z' | '_' | '$' | '#' | '.' | Digit)*
    ;

String
@after {
    setText(getText().substring(1, getText().length() - 1).replaceAll("\\\\(.)", "$1"));
}
    : '"' (~('"'))* '"'
    ;

Comment
    : '--' ~('\r' | '\n')* { skip(); }
    | '/*' .* '*/' { skip(); }
    ;

Space
    : (' ' | '\t') { skip(); }
    ;

NewLine
    : ('\r' | '\n' | '\u000C') { skip(); }
    ;

fragment Int
    : '1'..'9'
    | '0'
    ;

fragment Digit 
    : '0'..'9'
    ;

... and the following parser:

parser grammar CodeTableParser;

options {
    tokenVocab = CodeTableLexer;
    backtrack = true;
    output = AST;
}

@header {
   package ch.bsource.ice.parsers;
}

parse
    : block EOF
    ;

block
    : CodeTabHeader^ codeTable endCodeTable
    ;

codeTable
    : CodeTable^ codeTableData
    ;

codeTableData
    : (Identifier^ obsolete?) (tabdef | row)*
    ;

endCodeTable
    : EndCodeTable
    ;

tabdef
    : Tabdef^ Identifier+
    ;

row
    : Row^ rowData
    ;

rowData
    : (Number^ | (Identifier^ (Comma Number)?))
        Override?
        obsolete?
        status?
        Pkg?
        Ddic?
        (tab | field)*
    ;

tab
    : Tab^ value+
    ;

field
    : (Identifier^ value) | naming
    ;

value
    : OBracket? (Identifier | String | Number | Boolean | Null) CBracket?
    ;

naming
    : Naming^ defaultNaming (l10nNaming)*
    ;

defaultNaming
    : Dfltlang^ String
    ;

l10nNaming
    : Language^ String?
    ;

obsolete
    : Obsolete^ Substitute String
    ;

status
    : Status^ Override?
    ;

... finally my class for making the parser case-insensitive:

package ch.bsource.ice.parsers;

import java.io.IOException;
import org.antlr.runtime.*;

public class ANTLRNoCaseFileStream extends ANTLRFileStream {

    public ANTLRNoCaseFileStream(String fileName) throws IOException {

        super (fileName, null);
    }

    public ANTLRNoCaseFileStream(String fileName, String encoding) throws IOException {

        super (fileName, null);
    }

    public int LA(int i) {

        if (i == 0) return 0;
        if (i < 0) i++;
        if ((p + 1 - 1) >= n) return CharStream.EOF
        return Character.toLowerCase(data[p + 1 - 1]);
    }
}

... single-line comments are skipped as expected, while multi-line comments aren't... here is the error message I get:

codetable_1.txt line 38:0 mismatched character '<EOF>' expecting '*'
codetable_1.txt line 38:0 mismatched input '<EOF>' expecting EndCodeTable
java.lang.NullPointerException
...

Am I missing something? Is there anything I should be aware of? I'm using antlr 3.4.

Here is also the example source code I'm trying to parse:

[code table 1.0]

/*
This is a multi-line comment
*/

code table my_table

-- this is a single-line comment
row 1
    id              "my_id_1"
    name            "my_name_1"
    descn           "my_description_1"
    naming
      dfltlang      "My description 1"
      english       "My description 1"
      german        "Meine Beschreibung 1"

-- this is another single-line comment
row 2
    id              "my_id_2"
    name            "my_name_2"
    descn           "my_description_2"
    naming
      dfltlang      "My description 2"
      english       "My description 2"
      german        "Meine Beschreibung 2"

end code table

Any help would be really appreciated :-)

Thanks, j3d

回答1:

To do this in antlr4

BlockComment 
    : '/*' .*? '*/' -> skip
    ;

回答2:

Bart gave me an amazing support and I think we all really appreciate him :-)

Anyway, the problem was a bug in the FileStream class I use to convert parsed char stream to lowercase. Here below is the correct Java source code:

import java.io.IOException;
import org.antlr.runtime.*;

public class ANTLRNoCaseFileStream extends ANTLRFileStream {

    public ANTLRNoCaseFileStream(String fileName) throws IOException {

        super (fileName, null);
    }

    public ANTLRNoCaseFileStream(String fileName, String encoding) throws IOException {

        super (fileName, null);
    }

    public int LA(int i) {

        if (i == 0) return 0;
        if (i < 0) i++;
        if ((p + i - 1) >= n) return CharStream.EOF;
        return Character.toLowerCase(data[p + i - 1]);
    }
}

回答3:

I use 2 rules that I use to skip line and block comments (I print them during parsing for debug purposes). They are split in 2 for better readability, and the block comment does support nested comments.

Also, I do not skip EOL chars (\r and / or \n) in my grammar because I need them explicitly for some rules.

LineComment
    :   '//' ~('\n'|'\r')* //NEWLINE
        {System.out.println("lc > " + getText());
        skip();}
    ;

BlockComment
@init { int depthOfComments = 0;}
    :   '/*' {depthOfComments++;}
        ( options {greedy=false;}
        : ('/' '*')=> BlockComment {depthOfComments++;}
        | '/' ~('*')
        | ~('/')
        )*
        '*/' {depthOfComments--;}
        {
           if (depthOfComments == 0) {
                System.out.println("bc >" + getText());
                skip();
            }
        }
    ;