booleanLiteral terminals parsed as attributes in cql2-text

[duckontheweb]

System Info

Python Version: 3.10

OS: macOS Ventura 13.6.6

pygeofilter Version: 0.2.1 (main branch)

Problem Description

According to the OGC CQL2 documentation, a value of TRUE (case-insensitive) should be interpreted as a booleanLiteral value (see CQL2-Text example 14). So, for example, in the following query we should interpret attr as an attribute and TRUE as a booleanLiteral that we are comparing attr against:

attr = TRUE

However, the current CQL2 Text parser interprets the value of TRUE as an attribute. This leads to errors when we try to translate the AST to a backend like SQLAlchemy.

Steps to Reproduce:

from pygeofilter import ast
from pygeofilter.parsers.cql2_text import parse

result = parse("attr = TRUE")
assert result == ast.Equal(
    ast.Attribute("attr"),
    True,
)
# Assertion fails. The actual object is
# ast.Equal(
#     ast.Attribute("attr"),
#     ast.Attribute("TRUE")
# )

Possible Solution

I will put up a PR shortly with a possible solution that uses Lark's terminal priority to ensure that values of TRUE/true/FALSE/false are parsed as booleanLiteral values.