Support for Infix Operators in Liquid

[albchu]

Overview

This PR introduces a significant syntax improvement to Liquid templates:

Infix Operator Support: More intuitive mathematical and logical operations

This change makes templates more readable and concise by allowing developers to write expressions in a more natural way.

Changes

Infix Operator Support

• Add arithmetic operators: +, -, *, /
• Add comparison operators: >, >=, ==, <=, <
• Add logical operators: &&, ||
• Add XOR operator: ^
• Support operator precedence and parenthesized expressions

Before:

{% assign media_count = media_count | minus: variant_images.size | plus: 1 %}

After:

{% assign media_count = media_count - variant_images.size + 1 %}

Benefits

• More Readable Code: Expressions are written in a more natural and familiar syntax
• Less Verbose: Fewer characters and more straightforward expressions
• Easier Maintenance: Simpler syntax reduces cognitive load for developers
• Familiar Syntax: Follows conventions from other programming languages

Testing

Added a new test suite:

• infix_operators_unit_test.rb: Tests arithmetic, comparison, and logical operators

All tests should pass with the implementation.

[albchu]

Split this out from https://github.com/Shopify/liquid/pull/1922 because the work is massively more complex than is feasible to prioritize at this time. These unit tests can still be useful when we return to this.

[isaacbowen]

Liquid being postfix-y (with filter chaining and such), introducing infix feels as seismic as the Shopify Admin API going GraphQL.

This isn't good or bad, just a, uh, premonition. ;)