Fix Operator Precedence

[rcosta358]

This PR fixes operator precedence in the LiquidJava refinements, where e.g. the operators + and - had the same precedence as *, /, and %. This could lead to unexpected bugs and forced users to explicitly group expressions in parentheses.

Also, the grammar rejected some valid nested boolean expressions, such as "_ == (true || false && false)", because && and || were not allowed in the exp rule.

Finally, the parser could accept only a valid prefix of the expression. For example, the refinement true false would be accepted as true instead of throwing a syntax error, silently ignoring false.

Changes

The grammar now defines expression parsing in a single left-recursive pred rule, making the precedence order explicit, with the last two being right associative:

! → * / % → + - → == != >= > <= < → && → || → --> → ? :

To make sure the whole refinement string is consumed, prog: start | ; was changed to to prog: start EOF; and parser.start() to parser.prog().

Examples

@Refinement("_ == 1 + 2 * 0")
int x = 1;
// Before: Refinement Error: #x⁰ == 1 is not a subtype of #x⁰ == 0
// After: No error

@Refinement("_ == (true || false && false)")
// Before: Syntax Error
// After: No error

@Refinement("true false")
// Before: No error
// After: Syntax Error

[CatarinaGamboa]

ok this looks good

[CatarinaGamboa]

ok didnt know you could use <assoc=right>