Module: JekyllHighlightCards::ExpressionEvaluator

Included in:
LinkcardTag, PolaroidTag
Defined in:
lib/jekyll-highlight-cards/expression_evaluator.rb

Overview

Evaluate Liquid expressions and handle string values

Provides utilities for evaluating Liquid variables (e.g., {{ page.title }}) and processing string values with quote stripping and fallback behavior.

Examples:

Evaluate a Liquid variable

result = evaluate_expression("{{ page.title }}", context)

Evaluate a quoted string

result = evaluate_expression('"My Title"', context)  #=> "My Title"

Instance Method Summary collapse

Instance Method Details

#evaluate_expression(token, context, allow_nil: true) ⇒ String?

Evaluate a token as a Liquid expression or literal string

Parameters:

  • token (String) —

    the token to evaluate

  • context (Liquid::Context) —

    the Liquid context for variable resolution

  • allow_nil (Boolean) (defaults to: true) —

    whether to allow nil results

Returns:

  • (String, nil) —

    evaluated value or nil if evaluation fails



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 21

def evaluate_expression(token, context, allow_nil: true)
  # Strip outer quotes if present
  stripped = strip_outer_quotes(token)

  # If the original token was quoted, treat as literal string
  if !token.nil? && quote_wrapped?(token)
    return stripped if allow_nil

    return stripped.empty? ? nil : stripped
  end

  # Try to evaluate as Liquid expression
  if variable_lookup?(token)
    begin
      # Parse and evaluate the Liquid expression
      template = Liquid::Template.parse(token)
      result = template.render(context)
      return result if allow_nil

      return nil if result.empty?

      result
    rescue Liquid::SyntaxError, StandardError => e
      log_debug("Failed to evaluate '#{token}' as Liquid expression: #{e.class}: #{e}")
      token
    end
  else
    token
  end
end

#log_debug(message) ⇒ Object

Log debug message

Parameters:

  • message (String) —

    message to log



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 87

def log_debug(message)
  Jekyll.logger.debug("HighlightCards:", message)
end

#log_error(message) ⇒ Object

Log error message

Parameters:

  • message (String) —

    message to log



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 108

def log_error(message)
  Jekyll.logger.error("HighlightCards:", message)
end

#log_info(message) ⇒ Object

Log info message

Parameters:

  • message (String) —

    message to log



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 94

def log_info(message)
  Jekyll.logger.info("HighlightCards:", message)
end

#log_warn(message) ⇒ Object

Log warning message

Parameters:

  • message (String) —

    message to log



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 101

def log_warn(message)
  Jekyll.logger.warn("HighlightCards:", message)
end

#quote_wrapped?(value) ⇒ Boolean

Whether value has matching outer quotes and more than one character

Parameters:

  • value (String) —

    the string to inspect

Returns:

  • (Boolean) 


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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 77

def quote_wrapped?(value)
  return false unless value.length >= 2

  (value.start_with?('"') && value.end_with?('"')) ||
    (value.start_with?("'") && value.end_with?("'"))
end

#strip_outer_quotes(value) ⇒ String

Strip outer quotes from a string (both single and double quotes)

Parameters:

  • value (String) —

    the string to process

Returns:

  • (String) —

    string with outer quotes removed if present



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 66

def strip_outer_quotes(value)
  return nil if value.nil?
  return value[1..-2] if quote_wrapped?(value)

  value
end

#variable_lookup?(expression) ⇒ Boolean

Check if an expression looks like a Liquid variable lookup

Parameters:

  • expression (String) —

    the expression to check

Returns:

  • (Boolean) —

    true if expression contains Liquid syntax



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# File 'lib/jekyll-highlight-cards/expression_evaluator.rb', line 56

def variable_lookup?(expression)
  return false if expression.nil?

  expression.include?("{{") || expression.include?("{%")
end