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Class: SyntaxSuggest::CodeFrontier

Relationships & Source Files
Inherits: Object
Defined in: lib/syntax_suggest/code_frontier.rb

Overview

There are three main phases in the algorithm:

  1. Sanitize/format input source

  2. Search for invalid blocks

  3. Format invalid blocks into something meaninful

The Code frontier is a critical part of the second step

Knowing where we’ve been

Once a code block is generated it is added onto the frontier. Then it will be sorted by indentation and frontier can be filtered. Large blocks that fully enclose a smaller block will cause the smaller block to be evicted.

CodeFrontier#<<(block) # Adds block to frontier
CodeFrontier#pop # Removes block from frontier

Knowing where we can go

Internally the frontier keeps track of “unvisited” lines which are exposed via #next_indent_line when called, this method returns, a line of code with the highest indentation.

The returned line of code can be used to build a CodeBlock and then that code block is added back to the frontier. Then, the lines are removed from the “unvisited” so we don’t double-create the same block.

CodeFrontier#next_indent_line # Shows next line
CodeFrontier#register_indent_block(block) # Removes lines from unvisited

Knowing when to stop

The frontier knows how to check the entire document for a syntax error. When blocks are added onto the frontier, they’re removed from the document. When all code containing syntax errors has been added to the frontier, the document will be parsable without a syntax error and the search can stop.

CodeFrontier#holds_all_syntax_errors? # Returns true when frontier holds all syntax errors

Filtering false positives

Once the search is completed, the frontier may have multiple blocks that do not contain the syntax error. To limit the result to the smallest subset of “invalid blocks” call:

CodeFrontier#detect_invalid_blocks

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new(code_lines:, unvisited: UnvisitedLines.new(code_lines: code_lines)) ⇒ CodeFrontier

[ GitHub ] 

  


# File 'lib/syntax_suggest/code_frontier.rb', line 53



def initialize(code_lines:, unvisited: UnvisitedLines.new(code_lines: code_lines))
  @code_lines = code_lines
  @unvisited = unvisited
  @queue = PriorityEngulfQueue.new

  @check_next = true
end


  







Class Method Details



  

    .combination(array)  
  



  

    

Example:



combination([:a, :b, :c, :d])
# => [[:a], [:b], [:c], [:d], [:a, :b], [:a, :c], [:a, :d], [:b, :c], [:b, :d], [:c, :d], [:a, :b, :c], [:a, :b, :d], [:a, :c, :d], [:b, :c, :d], [:a, :b, :c, :d]]


  



  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 162



def self.combination(array)
  guesses = []
  1.upto(array.length).each do |size|
    guesses.concat(array.combination(size).to_a)
  end
  guesses
end


  







Instance Attribute Details



  

    #can_skip_check?  ⇒ Boolean  (readonly, private)
  



  

    

Performance optimization



Parsing with ripper is expensive If we know we don’t have any blocks with invalid syntax, then we know we cannot have found the incorrect syntax yet.



When an invalid block is added onto the frontier check document state


  





  


  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 74



private def can_skip_check?
  check_next = @check_next
  @check_next = false

  if check_next
    false
  else
    true
  end
end


  








  

    #expand?  ⇒ Boolean  (readonly)
  

  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 111



def expand?
  return false if @queue.empty?
  return true if @unvisited.empty?

  frontier_indent = @queue.peek.current_indent
  unvisited_indent = next_indent_line.indent

  if ENV["SYNTAX_SUGGEST_DEBUG"]
    puts "```"
    puts @queue.peek.to_s
    puts "```"
    puts "  @frontier indent:  #{frontier_indent}"
    puts "  @unvisited indent: #{unvisited_indent}"
  end

  # Expand all blocks before moving to unvisited lines
  frontier_indent >= unvisited_indent
end


  







Instance Method Details



  

    #<<(block)  
  



  

    

Add a block to the frontier



This method ensures the frontier always remains sorted (in indentation order) and that each code block’s lines are removed from the indentation hash so we don’t re-evaluate the same line multiple times.


  



  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 148



def <<(block)
  @unvisited.visit_block(block)

  @queue.push(block)

  @check_next = true if block.invalid?

  self
end


  








  

    #count  
  

  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 61



def count
  @queue.length
end


  








  

    #detect_invalid_blocks  
  



  

    

Given that we know our syntax error exists somewhere in our frontier, we want to find the smallest possible set of blocks that contain all the syntax errors


  



  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 172



def detect_invalid_blocks
  self.class.combination(@queue.to_a.select(&:invalid?)).detect do |block_array|
    holds_all_syntax_errors?(block_array, can_cache: false)
  end || []
end


  








  

    #holds_all_syntax_errors?(block_array = @queue, can_cache: true)  ⇒ Boolean 
  



  

    

Returns true if the document is valid with all lines removed. By default it checks all blocks in present in the frontier array, but can be used for arbitrary arrays of codeblocks as well


  





  


  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 89



def holds_all_syntax_errors?(block_array = @queue, can_cache: true)
  return false if can_cache && can_skip_check?

  without_lines = block_array.to_a.flat_map do |block|
    block.lines
  end

  SyntaxSuggest.valid_without?(
    without_lines: without_lines,
    code_lines: @code_lines
  )
end


  








  

    #next_indent_line  
  

  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 107



def next_indent_line
  @unvisited.peek
end


  








  

    #pop  
  



  

    

Returns a code block with the largest indentation possible


  



  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 103



def pop
  @queue.pop
end


  








  

    #register_engulf_block(block)  
  



  

    

When one element fully encapsulates another we remove the smaller block from the frontier. This prevents double expansions and all-around weird behavior. However this guarantee is quite expensive to maintain


  



  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 140



def register_engulf_block(block)
end


  








  

    #register_indent_block(block)  
  



  

    

Keeps track of what lines have been added to blocks and which are not yet visited.


  



  [ GitHub ]


  

  


# File 'lib/syntax_suggest/code_frontier.rb', line 132



def register_indent_block(block)
  @unvisited.visit_block(block)
  self
end