Unhandled syntax error: "else if" is parsed as "else"

The following template has invalid syntax:

{% if false %}
  1
{% else if false %}
  2
{% else %}
  3
{% endif %}

The else if should be elsif, but instead of a SyntaxError being raised, the template is parsed without error and the else if acts as an else. Thus, the above example will always produce 2. This else if should fail to parse since the else has a condition (relevant code).

This can be confusing to end-users since the template is successfully parsed, leading them to believe the template is valid.

Start by reading the conditional-tag parsing logic in lib/liquid/tags/if.rb around line 54. Verify how an else token with a condition is handled, then confirm that the provided template raises SyntaxError instead of rendering 2; done means invalid else conditions are rejected.