ANTLR4: wrong lexer rule matches - antlr

Question

I'm at a very beginning of learning ANTLR4 lexer rules. My goal is to create a simple grammar for Java properties files. Here is what I have so far:
lexer grammar PropertiesLexer;
LineComment
: ( LineCommentHash
| LineCommentExcl
)
-> skip
;
fragment LineCommentHash
: '#' ~[\r\n]*
;
fragment LineCommentExcl
: '!' ~[\r\n]*
;
fragment WrappedLine
: '\\'
( '\r' '\n'?
| '\n'
)
;
Newline
: ( '\r' '\n'?
| '\n'
)
-> skip
;
Key
: KeyLetterStart
( KeyLetter
| Escaped
)*
;
fragment KeyLetterStart
: ~[ \t\r\n:=]
;
fragment KeyLetter
: ~[\t\r\n:=]
;
fragment Escaped
: '\\' .?
;
Equal
: ( '\\'? ':'
| '\\'? '='
)
;
Value
: ValueLetterBegin
( ValueLetter
| Escaped
| WrappedLine
)*
;
fragment ValueLetterBegin
: ~[ \t\r\n]
;
fragment ValueLetter
: ~ [\r\n]+
;
Whitespace
: [ \t]+
-> skip
;
My test file is this one:
# comment 1
# comment 2
#
.key1= value1
key2\:sub=value2
key3 \= value3
key4=value41\
value42
# comment3
#comment4
key=value
When I run grun, I'm getting following output:
[#0,30:42='.key1= value1',<Value>,4:0]
[#1,45:60='key2\:sub=value2',<Value>,5:0]
[#2,63:76='key3 \= value3',<Value>,6:0]
[#3,81:102='key4=value41\\r\nvalue42',<Value>,8:0]
[#4,130:138='key=value',<Value>,13:0]
[#5,141:140='<EOF>',<EOF>,14:0]
I don't understand why the Value definition is matched. When commenting out the Value definition, however, it recognizes the Key and Equal definitions:
[#0,30:34='.key1',<Key>,4:0]
[#1,35:35='=',<Equal>,4:5]
[#2,37:42='value1',<Key>,4:7]
[#3,45:49='key2\',<Key>,5:0]
[#4,50:50=':',<Equal>,5:5]
[#5,51:53='sub',<Key>,5:6]
[#6,54:54='=',<Equal>,5:9]
[#7,55:60='value2',<Key>,5:10]
[#8,63:68='key3 \',<Key>,6:0]
[#9,69:69='=',<Equal>,6:6]
[#10,71:76='value3',<Key>,6:8]
[#11,81:84='key4',<Key>,8:0]
[#12,85:85='=',<Equal>,8:4]
[#13,86:93='value41\',<Key>,8:5]
[#14,96:102='value42',<Key>,9:0]
[#15,130:132='key',<Key>,13:0]
[#16,133:133='=',<Equal>,13:3]
[#17,134:138='value',<Key>,13:4]
[#18,141:140='<EOF>',<EOF>,14:0]
but how to let it recognize the Key, Equal and Value definitons?

Answer 1

ANTLR's lexer rules match as much characters as possible, that is why you're seeing all these Value tokens being created (they match the most characters).
Lexical modes seem like a good fit to use here. Something like this:
lexer grammar PropertiesLexer;
COMMENT
: [!#] ~[\r\n]* -> skip
;
KEY
: ( '\\' ~[\r\n] | ~[\r\n\\=:] )+
;
EQUAL
: [=:] -> pushMode(VALUE_MODE)
;
NL
: [\r\n]+ -> skip
;
mode VALUE_MODE;
VALUE
: ( ~[\\\r\n] | '\\' . )+
;
END_VALUE
: [\r\n]+ -> skip, popMode
;