Parse negative numbers as values, not as unary expressions containg a literal (fixes #421)

Author: desplesda

Tests/TestCases/SmartVariables.yarn

@@ -14,6 +14,10 @@ title: Start
     PieMaker: You can't afford one!
 <<endif>>
 
+// Negative numbers are not interpreted as smart variables (issue #421)
+<<declare $x = -1>>
+<<set $x += 1>>
+
 // Variables are allowed to appear multiple times in a smart variable
 <<declare $a = false as bool>>
 <<declare $b = false as bool>>

YarnSpinner.Compiler/Grammars/YarnSpinnerLexer.cs

@@ -230,6 +230,12 @@ KEYWORD_TRUE  : 'true' ;
 KEYWORD_FALSE : 'false' ;
 KEYWORD_NULL : 'null' ;
 
+// Integer or decimal numbers.
+NUMBER
+    : ('-')? INT
+    | ('-')? INT '.' INT
+    ;
+
 OPERATOR_ASSIGNMENT : '=' | 'to' ;
 
 OPERATOR_LOGICAL_LESS_THAN_EQUALS : '<=' | 'lte' ;
@@ -280,12 +286,6 @@ VAR_ID : '$' ID ;
 // Dots ('.')
 DOT : '.' ;
 
-// Integer or decimal numbers.
-NUMBER
-    : INT
-    | INT '.' INT
-    ;
-
 // Newlines (only syntactically relevant when inside a 'when' clause). 
 // We use a newline to indicate that the expression is over, but only
 // when we're in a 'when' clause - in all other expressions, newlines are 

YarnSpinner.Compiler/Grammars/YarnSpinnerLexer.g4

@@ -33,37 +33,37 @@ EXPRESSION_WHEN_ALWAYS=32
 KEYWORD_TRUE=33
 KEYWORD_FALSE=34
 KEYWORD_NULL=35
-OPERATOR_ASSIGNMENT=36
-OPERATOR_LOGICAL_LESS_THAN_EQUALS=37
-OPERATOR_LOGICAL_GREATER_THAN_EQUALS=38
-OPERATOR_LOGICAL_EQUALS=39
-OPERATOR_LOGICAL_LESS=40
-OPERATOR_LOGICAL_GREATER=41
-OPERATOR_LOGICAL_NOT_EQUALS=42
-OPERATOR_LOGICAL_AND=43
-OPERATOR_LOGICAL_OR=44
-OPERATOR_LOGICAL_XOR=45
-OPERATOR_LOGICAL_NOT=46
-OPERATOR_MATHS_ADDITION_EQUALS=47
-OPERATOR_MATHS_SUBTRACTION_EQUALS=48
-OPERATOR_MATHS_MULTIPLICATION_EQUALS=49
-OPERATOR_MATHS_MODULUS_EQUALS=50
-OPERATOR_MATHS_DIVISION_EQUALS=51
-OPERATOR_MATHS_ADDITION=52
-OPERATOR_MATHS_SUBTRACTION=53
-OPERATOR_MATHS_MULTIPLICATION=54
-OPERATOR_MATHS_DIVISION=55
-OPERATOR_MATHS_MODULUS=56
-LPAREN=57
-RPAREN=58
-COMMA=59
-EXPRESSION_AS=60
-STRING=61
-FUNC_ID=62
-EXPRESSION_END=63
-VAR_ID=64
-DOT=65
-NUMBER=66
+NUMBER=36
+OPERATOR_ASSIGNMENT=37
+OPERATOR_LOGICAL_LESS_THAN_EQUALS=38
+OPERATOR_LOGICAL_GREATER_THAN_EQUALS=39
+OPERATOR_LOGICAL_EQUALS=40
+OPERATOR_LOGICAL_LESS=41
+OPERATOR_LOGICAL_GREATER=42
+OPERATOR_LOGICAL_NOT_EQUALS=43
+OPERATOR_LOGICAL_AND=44
+OPERATOR_LOGICAL_OR=45
+OPERATOR_LOGICAL_XOR=46
+OPERATOR_LOGICAL_NOT=47
+OPERATOR_MATHS_ADDITION_EQUALS=48
+OPERATOR_MATHS_SUBTRACTION_EQUALS=49
+OPERATOR_MATHS_MULTIPLICATION_EQUALS=50
+OPERATOR_MATHS_MODULUS_EQUALS=51
+OPERATOR_MATHS_DIVISION_EQUALS=52
+OPERATOR_MATHS_ADDITION=53
+OPERATOR_MATHS_SUBTRACTION=54
+OPERATOR_MATHS_MULTIPLICATION=55
+OPERATOR_MATHS_DIVISION=56
+OPERATOR_MATHS_MODULUS=57
+LPAREN=58
+RPAREN=59
+COMMA=60
+EXPRESSION_AS=61
+STRING=62
+FUNC_ID=63
+EXPRESSION_END=64
+VAR_ID=65
+DOT=66
 COMMAND_NEWLINE=67
 COMMAND_WS=68
 COMMAND_IF=69
@@ -103,25 +103,25 @@ TYPE_BOOL=93
 'true'=33
 'false'=34
 'null'=35
-'+='=47
-'-='=48
-'*='=49
-'%='=50
-'/='=51
-'+'=52
-'-'=53
-'*'=54
-'/'=55
-'%'=56
-'('=57
-')'=58
-','=59
-'as'=60
+'+='=48
+'-='=49
+'*='=50
+'%='=51
+'/='=52
+'+'=53
+'-'=54
+'*'=55
+'/'=56
+'%'=57
+'('=58
+')'=59
+','=60
+'as'=61
 'string'=91
 'number'=92
 'bool'=93
-'}'=63
-'.'=65
+'}'=64
+'.'=66
 'else'=71
 'endif'=73
 'return'=78