Error when generating a grammar for chess PGN files - antlr4

Question

I made this ANTLR4 grammar in order to parse a PGN inside my Java programm, but I can't manage to solve the ambiguity in it :
grammar Pgn;
file: game (NEWLINE+ game)*;
game: (tag+ NEWLINE+)? notation;
tag: [TAG_TYPE "TAG_VALUE"];
notation: move+ END_RESULT?;
move: MOVE_NUMBER\. MOVE_DESC MOVE_DESC #CompleteMove
| MOVE_NUMBER\. MOVE_DESC #OnlyWhiteMove
| MOVE_NUMBER\.\.\. MOVE_DESC #OnlyBlackMove
;
END_RESULT: '1-0'
| '0-1'
| '1/2-1/2'
;
TAG_TYPE: LETTER+;
TAG_VALUE: .*;
MOVE_NUMBER: DIGIT+;
MOVE_DESC: .*;
NEWLINE: \r? \n;
SPACES: [ \t]+ -> skip;
fragment LETTER: [a-zA-Z];
fragment DIGIT: [0-9];
And this is the error output :
$ antlr4 Pgn.g4
error(50): Pgn.g4:6:6: syntax error: 'TAG_TYPE "TAG_VALUE"' came as a complete surprise to me while matching alternative
I think the error come from the fact that " [ ", " ] " and ' " ' can't be used freely, neither in Grammar nor Lexer.
Helps or advices are welcome.

Answer 1

Looking at the specs for PGN, http://www.thechessdrum.net/PGN_Reference.txt, I see there's a formal definition of the PGN format there:
18: Formal syntax
<PGN-database> ::= <PGN-game> <PGN-database>
<empty>
<PGN-game> ::= <tag-section> <movetext-section>
<tag-section> ::= <tag-pair> <tag-section>
<empty>
<tag-pair> ::= [ <tag-name> <tag-value> ]
<tag-name> ::= <identifier>
<tag-value> ::= <string>
<movetext-section> ::= <element-sequence> <game-termination>
<element-sequence> ::= <element> <element-sequence>
<recursive-variation> <element-sequence>
<empty>
<element> ::= <move-number-indication>
<SAN-move>
<numeric-annotation-glyph>
<recursive-variation> ::= ( <element-sequence> )
<game-termination> ::= 1-0
0-1
1/2-1/2
*
<empty> ::=
I highly recommend you to let your ANTLR grammar resemble that as much as possible. I made a small project with ANTLR 4 on Github which you can try out: https://github.com/bkiers/PGN-parser
The grammar (without comments):
parse
: pgn_database EOF
;
pgn_database
: pgn_game*
;
pgn_game
: tag_section movetext_section
;
tag_section
: tag_pair*
;
tag_pair
: LEFT_BRACKET tag_name tag_value RIGHT_BRACKET
;
tag_name
: SYMBOL
;
tag_value
: STRING
;
movetext_section
: element_sequence game_termination
;
element_sequence
: (element | recursive_variation)*
;
element
: move_number_indication
| san_move
| NUMERIC_ANNOTATION_GLYPH
;
move_number_indication
: INTEGER PERIOD?
;
san_move
: SYMBOL
;
recursive_variation
: LEFT_PARENTHESIS element_sequence RIGHT_PARENTHESIS
;
game_termination
: WHITE_WINS
| BLACK_WINS
| DRAWN_GAME
| ASTERISK
;
WHITE_WINS
: '1-0'
;
BLACK_WINS
: '0-1'
;
DRAWN_GAME
: '1/2-1/2'
;
REST_OF_LINE_COMMENT
: ';' ~[\r\n]* -> skip
;
BRACE_COMMENT
: '{' ~'}'* '}' -> skip
;
ESCAPE
: {getCharPositionInLine() == 0}? '%' ~[\r\n]* -> skip
;
SPACES
: [ \t\r\n]+ -> skip
;
STRING
: '"' ('\\\\' | '\\"' | ~[\\"])* '"'
;
INTEGER
: [0-9]+
;
PERIOD
: '.'
;
ASTERISK
: '*'
;
LEFT_BRACKET
: '['
;
RIGHT_BRACKET
: ']'
;
LEFT_PARENTHESIS
: '('
;
RIGHT_PARENTHESIS
: ')'
;
LEFT_ANGLE_BRACKET
: '<'
;
RIGHT_ANGLE_BRACKET
: '>'
;
NUMERIC_ANNOTATION_GLYPH
: '$' [0-9]+
;
SYMBOL
: [a-zA-Z0-9] [a-zA-Z0-9_+#=:-]*
;
SUFFIX_ANNOTATION
: [?!] [?!]?
;
UNEXPECTED_CHAR
: .
;
For a version with comments, see: https://github.com/bkiers/PGN-parser/blob/master/src/main/antlr4/nl/bigo/pp/PGN.g4