Class: Rhales::HandlebarsParser

Inherits:
Object
  • Object
show all
Defined in:
lib/rhales/parsers/handlebars_parser.rb

Overview

Hand-rolled recursive descent parser for Handlebars template syntax

This parser implements Handlebars parsing rules in Ruby code and produces an Abstract Syntax Tree (AST) for template processing. It handles:

  • Variable expressions: {variable}, {{raw}}
  • Block expressions: {{#if}{else}{/if}, {{#each}{/each}
  • Partials: partial_name}
  • Proper nesting and error reporting
  • Whitespace control (future)

Note: This class is a parser implementation, not a formal grammar definition. A formal grammar would be written in BNF/EBNF notation, while this class contains the actual parsing logic written in Ruby.

AST Node Types: - :template - Root template node - :text - Plain text content - :variable_expression - {variable} or {{variable}} - :if_block - {{#if}…{else}…{/if} - :unless_block - {{#unless}…{/unless} - :each_block - {{#each}…{/each} - :partial_expression - partial}

Defined Under Namespace

Classes: Location, Node, ParseError

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(content) ⇒ HandlebarsParser

Returns a new instance of HandlebarsParser.



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 64

def initialize(content)
  @content  = content
  @position = 0
  @line     = 1
  @column   = 1
  @ast      = nil
end

Instance Attribute Details

#ast ⇒ Object (readonly)

Returns the value of attribute ast.



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 62

def ast
  @ast
end

#content ⇒ Object (readonly)

Returns the value of attribute content.



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 62

def content
  @content
end

Instance Method Details

#advance ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 690

def advance
  if current_char == "\n"
    @line  += 1
    @column = 1
  else
    @column += 1
  end
  @position += 1
end

#at_end? ⇒ Boolean (private)

Returns:

  • (Boolean) 


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# File 'lib/rhales/parsers/handlebars_parser.rb', line 700

def at_end?
  @position >= @content.length
end

#blocks ⇒ Object 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 89

def blocks
  return [] unless @ast

  collect_blocks(@ast)
end

#collect_blocks(node) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 644

def collect_blocks(node)
  blocks = []

  case node.type
  when :if_block, :unless_block, :each_block
    blocks << node
    # Also collect nested blocks
    if node.type == :if_block
      blocks.concat(node.value[:if_content].flat_map { |child| collect_blocks(child) })
      blocks.concat(node.value[:else_content].flat_map { |child| collect_blocks(child) })
    else
      blocks.concat(node.value[:content].flat_map { |child| collect_blocks(child) })
    end
  else
    blocks.concat(node.children.flat_map { |child| collect_blocks(child) })
  end

  blocks
end

#collect_partials(node) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 626

def collect_partials(node)
  partials = []

  case node.type
  when :partial_expression
    partials << node.value[:name]
  when :if_block
    partials.concat(node.value[:if_content].flat_map { |child| collect_partials(child) })
    partials.concat(node.value[:else_content].flat_map { |child| collect_partials(child) })
  when :unless_block, :each_block
    partials.concat(node.value[:content].flat_map { |child| collect_partials(child) })
  else
    partials.concat(node.children.flat_map { |child| collect_partials(child) })
  end

  partials.uniq
end

#collect_variables(node) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 603

def collect_variables(node)
  variables = []

  case node.type
  when :variable_expression
    variables << node.value[:name]
  when :if_block
    variables << node.value[:condition]
    variables.concat(node.value[:if_content].flat_map { |child| collect_variables(child) })
    variables.concat(node.value[:else_content].flat_map { |child| collect_variables(child) })
  when :unless_block
    variables << node.value[:condition]
    variables.concat(node.value[:content].flat_map { |child| collect_variables(child) })
  when :each_block
    variables << node.value[:items]
    variables.concat(node.value[:content].flat_map { |child| collect_variables(child) })
  else
    variables.concat(node.children.flat_map { |child| collect_variables(child) })
  end

  variables.uniq
end

#consume(expected) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 681

def consume(expected)
  if peek_string?(expected)
    expected.length.times { advance }
    true
  else
    false
  end
end

#create_each_block(items_expression, start_location) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 394

def create_each_block(items_expression, start_location)
  # Parse the each block content
  content = []
  depth   = 1

  while !at_end? && depth > 0
    if current_char == '{' && peek_char == '{'
      expr_start = current_position
      consume('{{')

      raw = false
      if current_char == '{'
        raw = true
        advance
      end

      skip_whitespace
      expr_content = parse_expression_content(raw)
      skip_whitespace

      if raw
        consume('}}}') || parse_error("Expected '}}}'")
      else
        consume('}}') || parse_error("Expected '}}'")
      end

      expr_end      = current_position
      expr_location = create_location(expr_start, expr_end)

      case expr_content
      when /^#if\s+(.+)$/, /^#unless\s+(.+)$/, /^#each\s+(.+)$/
        depth += 1
        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when %r{^/each$}
        depth -= 1
        break if depth == 0

        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )

      when %r{^/if$}, %r{^/unless$}
        depth -= 1
        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when 'else'
        # This else belongs to a nested if block, not this each block
        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      else
        content << create_expression_node(expr_content, raw, expr_location)
      end
    else
      text_content = parse_text_until_handlebars
      content << create_text_node(text_content) unless text_content.empty?
    end
  end

  if depth > 0
    parse_error('Missing closing tag for {{#each}}')
  end

  processed_content = post_process_content(content)

  Node.new(:each_block, start_location, value: {
    items: items_expression,
    content: processed_content,
  }
  )
end

#create_expression_node(content, raw, location) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 172

def create_expression_node(content, raw, location)
  case content
  when /^#if\s+(.+)$/
    create_if_block(Regexp.last_match(1).strip, location)
  when /^#unless\s+(.+)$/
    create_unless_block(Regexp.last_match(1).strip, location)
  when /^#each\s+(.+)$/
    create_each_block(Regexp.last_match(1).strip, location)
  when /^>\s*(.+)$/
    create_partial_node(Regexp.last_match(1).strip, location)
  when %r{^/(.+)$}
    # This is a closing tag, should be handled by block parsing
    parse_error("Unexpected closing tag: #{content}")
  when 'else'
    # This should be handled by block parsing
    parse_error("Unexpected 'else' outside of block")
  else
    # Variable expression
    create_variable_node(content, raw, location)
  end
end

#create_if_block(condition, start_location) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 194

def create_if_block(condition, start_location)
  # Parse the if block content
  if_content      = []
  else_content    = []
  current_content = if_content
  depth           = 1

  while !at_end? && depth > 0
    if current_char == '{' && peek_char == '{'
      expr_start = current_position
      consume('{{')

      # Check for triple braces
      raw = false
      if current_char == '{'
        raw = true
        advance
      end

      skip_whitespace
      expr_content = parse_expression_content(raw)
      skip_whitespace

      if raw
        consume('}}}') || parse_error("Expected '}}}'")
      else
        consume('}}') || parse_error("Expected '}}'")
      end

      expr_end      = current_position
      expr_location = create_location(expr_start, expr_end)

      case expr_content
      when /^#if\s+(.+)$/
        depth += 1
        # Add as variable expression, will be parsed properly later
        current_content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when /^#unless\s+(.+)$/
        depth += 1
        current_content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when /^#each\s+(.+)$/
        depth += 1
        current_content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when %r{^/if$}
        depth -= 1
        break if depth == 0

        # Found the matching closing tag

        # This is a nested closing tag
        current_content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )

      when %r{^/unless$}
        depth -= 1
        current_content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when %r{^/each$}
        depth -= 1
        current_content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when 'else'
        if depth == 1
          current_content = else_content
        else
          current_content << Node.new(:variable_expression, expr_location, value: {
            name: expr_content,
            raw: raw,
          }
          )
        end
      else
        current_content << create_expression_node(expr_content, raw, expr_location)
      end
    else
      text_content = parse_text_until_handlebars
      current_content << create_text_node(text_content) unless text_content.empty?
    end
  end

  if depth > 0
    parse_error('Missing closing tag for {{#if}}')
  end

  # Now post-process the content to handle nested blocks
  processed_if_content   = post_process_content(if_content)
  processed_else_content = post_process_content(else_content)

  Node.new(:if_block, start_location, value: {
    condition: condition,
    if_content: processed_if_content,
    else_content: processed_else_content,
  }
  )
end

#create_location(start_pos, end_pos) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 712

def create_location(start_pos, end_pos)
  Location.new(
    start_line: start_pos[:line],
    start_column: start_pos[:column],
    end_line: end_pos[:line],
    end_column: end_pos[:column],
    start_offset: start_pos[:offset],
    end_offset: end_pos[:offset],
  )
end

#create_partial_node(name, location) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 485

def create_partial_node(name, location)
  Node.new(:partial_expression, location, value: {
    name: name,
  }
  )
end

#create_text_node(text) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 492

def create_text_node(text)
  pos      = current_position
  location = create_location(pos, pos)
  Node.new(:text, location, value: text)
end

#create_unless_block(condition, start_location) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 311

def create_unless_block(condition, start_location)
  # Parse the unless block content
  content = []
  depth   = 1

  while !at_end? && depth > 0
    if current_char == '{' && peek_char == '{'
      expr_start = current_position
      consume('{{')

      raw = false
      if current_char == '{'
        raw = true
        advance
      end

      skip_whitespace
      expr_content = parse_expression_content(raw)
      skip_whitespace

      if raw
        consume('}}}') || parse_error("Expected '}}}'")
      else
        consume('}}') || parse_error("Expected '}}'")
      end

      expr_end      = current_position
      expr_location = create_location(expr_start, expr_end)

      case expr_content
      when /^#if\s+(.+)$/, /^#unless\s+(.+)$/, /^#each\s+(.+)$/
        depth += 1
        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when %r{^/unless$}
        depth -= 1
        break if depth == 0

        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )

      when %r{^/if$}, %r{^/each$}
        depth -= 1
        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      when 'else'
        # This else belongs to a nested if block, not this unless block
        content << Node.new(:variable_expression, expr_location, value: {
          name: expr_content,
          raw: raw,
        }
        )
      else
        content << create_expression_node(expr_content, raw, expr_location)
      end
    else
      text_content = parse_text_until_handlebars
      content << create_text_node(text_content) unless text_content.empty?
    end
  end

  if depth > 0
    parse_error('Missing closing tag for {{#unless}}')
  end

  processed_content = post_process_content(content)

  Node.new(:unless_block, start_location, value: {
    condition: condition,
    content: processed_content,
  }
  )
end

#create_variable_node(name, raw, location) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 477

def create_variable_node(name, raw, location)
  Node.new(:variable_expression, location, value: {
    name: name,
    raw: raw,
  }
  )
end

#current_char ⇒ Object (private)

Utility methods



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 665

def current_char
  return "\0" if at_end?

  @content[@position]
end

#current_position ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 708

def current_position
  { line: @line, column: @column, offset: @position }
end

#extract_block_content_from_array(content, start_index, block_type) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 552

def extract_block_content_from_array(content, start_index, block_type)
  block_content   = []
  else_content    = []
  current_content = block_content
  depth           = 1
  i               = start_index

  while i < content.length && depth > 0
    node = content[i]

    if node.type == :variable_expression
      case node.value[:name]
      when /^##{block_type}\s+/
        depth += 1
        current_content << node
      when %r{^/#{block_type}$}
        depth -= 1
        return [block_content, else_content, i + 1] if depth == 0

        current_content << node

      when 'else'
        if block_type == 'if' && depth == 1
          current_content = else_content
        else
          current_content << node
        end
      else
        current_content << node
      end
    else
      current_content << node
    end

    i += 1
  end

  [block_content, else_content, i]
end

#parse! ⇒ Object 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 72

def parse!
  @ast = parse_template
  self
end

#parse_error(message) ⇒ Object (private)

Raises:



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 723

def parse_error(message)
  raise ParseError.new(message, line: @line, column: @column, offset: @position)
end

#parse_expression_content(raw) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 147

def parse_expression_content(raw)
  chars          = []
  closing_braces = raw ? '}}}' : '}}'
  brace_count    = 0

  until at_end?
    if current_char == '}' && peek_string?(closing_braces)
      break
    elsif current_char == '{' && peek_char == '{'
      # Handle nested braces in content
      brace_count += 1
    elsif current_char == '}' && peek_char == '}'
      brace_count -= 1
      if brace_count < 0
        break
      end
    end

    chars << current_char
    advance
  end

  chars.join.strip
end

#parse_handlebars_expression ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 115

def parse_handlebars_expression
  start_pos = current_position

  consume('{{') || parse_error("Expected '{{'")

  # Check for triple braces (raw output)
  raw = false
  if current_char == '{'
    raw = true
    advance
  end

  skip_whitespace

  # Parse expression content
  expression_content = parse_expression_content(raw)
  skip_whitespace

  # Consume closing braces
  if raw
    consume('}}}') || parse_error("Expected '}}}'")
  else
    consume('}}') || parse_error("Expected '}}'")
  end

  end_pos  = current_position
  location = create_location(start_pos, end_pos)

  # Determine expression type and create appropriate node
  create_expression_node(expression_content, raw, location)
end

#parse_template ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 97

def parse_template
  start_pos = current_position
  children  = []

  until at_end?
    if current_char == '{' && peek_char == '{'
      children << parse_handlebars_expression
    else
      text_content = parse_text_until_handlebars
      children << create_text_node(text_content) unless text_content.empty?
    end
  end

  end_pos  = current_position
  location = create_location(start_pos, end_pos)
  Node.new(:template, location, children: children)
end

#parse_text_until_handlebars ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 592

def parse_text_until_handlebars
  chars = []

  while !at_end? && !(current_char == '{' && peek_char == '{')
    chars << current_char
    advance
  end

  chars.join
end

#partials ⇒ Object 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 83

def partials
  return [] unless @ast

  collect_partials(@ast)
end

#peek_char ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 671

def peek_char
  return "\0" if @position + 1 >= @content.length

  @content[@position + 1]
end

#peek_string?(string) ⇒ Boolean (private)

Returns:

  • (Boolean) 


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# File 'lib/rhales/parsers/handlebars_parser.rb', line 677

def peek_string?(string)
  @content[@position, string.length] == string
end

#post_process_content(content) ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 498

def post_process_content(content)
  # Convert variable expressions that are actually block expressions
  processed = []
  i         = 0

  while i < content.length
    node = content[i]

    if node.type == :variable_expression
      case node.value[:name]
      when /^#if\s+(.+)$/
        condition                           = Regexp.last_match(1).strip
        if_content, else_content, end_index = extract_block_content_from_array(content, i + 1, 'if')
        processed << Node.new(:if_block, node.location, value: {
          condition: condition,
          if_content: post_process_content(if_content),
          else_content: post_process_content(else_content),
        }
        )
        i                                   = end_index
      when /^#unless\s+(.+)$/
        condition                   = Regexp.last_match(1).strip
        block_content, _, end_index = extract_block_content_from_array(content, i + 1, 'unless')
        processed << Node.new(:unless_block, node.location, value: {
          condition: condition,
          content: post_process_content(block_content),
        }
        )
        i                           = end_index
      when /^#each\s+(.+)$/
        items                       = Regexp.last_match(1).strip
        block_content, _, end_index = extract_block_content_from_array(content, i + 1, 'each')
        processed << Node.new(:each_block, node.location, value: {
          items: items,
          content: post_process_content(block_content),
        }
        )
        i                           = end_index
      when %r{^/\w+$}, 'else'
        # Skip closing tags and else - they're handled by block extraction
        i += 1
      else
        processed << node
        i += 1
      end
    else
      processed << node
      i += 1
    end
  end

  processed
end

#skip_whitespace ⇒ Object (private) 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 704

def skip_whitespace
  advance while !at_end? && current_char.match?(/\s/)
end

#variables ⇒ Object 



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# File 'lib/rhales/parsers/handlebars_parser.rb', line 77

def variables
  return [] unless @ast

  collect_variables(@ast)
end