Sync SyntaxSuggest

```
$ tool/sync_default_gems.rb syntax_suggest
```

lib/syntax_suggest.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+require_relative "syntax_suggest/core_ext"

lib/syntax_suggest/api.rb

@@ -0,0 +1,199 @@
+# frozen_string_literal: true
+
+require_relative "version"
+
+require "tmpdir"
+require "stringio"
+require "pathname"
+require "ripper"
+require "timeout"
+
+module SyntaxSuggest
+  # Used to indicate a default value that cannot
+  # be confused with another input.
+  DEFAULT_VALUE = Object.new.freeze
+
+  class Error < StandardError; end
+  TIMEOUT_DEFAULT = ENV.fetch("SYNTAX_SUGGEST_TIMEOUT", 1).to_i
+
+  # SyntaxSuggest.handle_error [Public]
+  #
+  # Takes a `SyntaxError` exception, uses the
+  # error message to locate the file. Then the file
+  # will be analyzed to find the location of the syntax
+  # error and emit that location to stderr.
+  #
+  # Example:
+  #
+  #   begin
+  #     require 'bad_file'
+  #   rescue => e
+  #     SyntaxSuggest.handle_error(e)
+  #   end
+  #
+  # By default it will re-raise the exception unless
+  # `re_raise: false`. The message output location
+  # can be configured using the `io: $stderr` input.
+  #
+  # If a valid filename cannot be determined, the original
+  # exception will be re-raised (even with
+  # `re_raise: false`).
+  def self.handle_error(e, re_raise: true, io: $stderr)
+    unless e.is_a?(SyntaxError)
+      io.puts("SyntaxSuggest: Must pass a SyntaxError, got: #{e.class}")
+      raise e
+    end
+
+    file = PathnameFromMessage.new(e.message, io: io).call.name
+    raise e unless file
+
+    io.sync = true
+
+    call(
+      io: io,
+      source: file.read,
+      filename: file
+    )
+
+    raise e if re_raise
+  end
+
+  # SyntaxSuggest.call [Private]
+  #
+  # Main private interface
+  def self.call(source:, filename: DEFAULT_VALUE, terminal: DEFAULT_VALUE, record_dir: DEFAULT_VALUE, timeout: TIMEOUT_DEFAULT, io: $stderr)
+    search = nil
+    filename = nil if filename == DEFAULT_VALUE
+    Timeout.timeout(timeout) do
+      record_dir ||= ENV["DEBUG"] ? "tmp" : nil
+      search = CodeSearch.new(source, record_dir: record_dir).call
+    end
+
+    blocks = search.invalid_blocks
+    DisplayInvalidBlocks.new(
+      io: io,
+      blocks: blocks,
+      filename: filename,
+      terminal: terminal,
+      code_lines: search.code_lines
+    ).call
+  rescue Timeout::Error => e
+    io.puts "Search timed out SYNTAX_SUGGEST_TIMEOUT=#{timeout}, run with DEBUG=1 for more info"
+    io.puts e.backtrace.first(3).join($/)
+  end
+
+  # SyntaxSuggest.record_dir [Private]
+  #
+  # Used to generate a unique directory to record
+  # search steps for debugging
+  def self.record_dir(dir)
+    time = Time.now.strftime("%Y-%m-%d-%H-%M-%s-%N")
+    dir = Pathname(dir)
+    dir.join(time).tap { |path|
+      path.mkpath
+      FileUtils.ln_sf(time, dir.join("last"))
+    }
+  end
+
+  # SyntaxSuggest.valid_without? [Private]
+  #
+  # This will tell you if the `code_lines` would be valid
+  # if you removed the `without_lines`. In short it's a
+  # way to detect if we've found the lines with syntax errors
+  # in our document yet.
+  #
+  #   code_lines = [
+  #     CodeLine.new(line: "def foo\n",   index: 0)
+  #     CodeLine.new(line: "  def bar\n", index: 1)
+  #     CodeLine.new(line: "end\n",       index: 2)
+  #   ]
+  #
+  #   SyntaxSuggest.valid_without?(
+  #     without_lines: code_lines[1],
+  #     code_lines: code_lines
+  #   )                                    # => true
+  #
+  #   SyntaxSuggest.valid?(code_lines) # => false
+  def self.valid_without?(without_lines:, code_lines:)
+    lines = code_lines - Array(without_lines).flatten
+
+    if lines.empty?
+      true
+    else
+      valid?(lines)
+    end
+  end
+
+  # SyntaxSuggest.invalid? [Private]
+  #
+  # Opposite of `SyntaxSuggest.valid?`
+  def self.invalid?(source)
+    source = source.join if source.is_a?(Array)
+    source = source.to_s
+
+    Ripper.new(source).tap(&:parse).error?
+  end
+
+  # SyntaxSuggest.valid? [Private]
+  #
+  # Returns truthy if a given input source is valid syntax
+  #
+  #   SyntaxSuggest.valid?(<<~EOM) # => true
+  #     def foo
+  #     end
+  #   EOM
+  #
+  #   SyntaxSuggest.valid?(<<~EOM) # => false
+  #     def foo
+  #       def bar # Syntax error here
+  #     end
+  #   EOM
+  #
+  # You can also pass in an array of lines and they'll be
+  # joined before evaluating
+  #
+  #   SyntaxSuggest.valid?(
+  #     [
+  #       "def foo\n",
+  #       "end\n"
+  #     ]
+  #   ) # => true
+  #
+  #   SyntaxSuggest.valid?(
+  #     [
+  #       "def foo\n",
+  #       "  def bar\n", # Syntax error here
+  #       "end\n"
+  #     ]
+  #   ) # => false
+  #
+  # As an FYI the CodeLine class instances respond to `to_s`
+  # so passing a CodeLine in as an object or as an array
+  # will convert it to it's code representation.
+  def self.valid?(source)
+    !invalid?(source)
+  end
+end
+
+# Integration
+require_relative "cli"
+
+# Core logic
+require_relative "code_search"
+require_relative "code_frontier"
+require_relative "explain_syntax"
+require_relative "clean_document"
+
+# Helpers
+require_relative "lex_all"
+require_relative "code_line"
+require_relative "code_block"
+require_relative "block_expand"
+require_relative "ripper_errors"
+require_relative "priority_queue"
+require_relative "unvisited_lines"
+require_relative "around_block_scan"
+require_relative "priority_engulf_queue"
+require_relative "pathname_from_message"
+require_relative "display_invalid_blocks"
+require_relative "parse_blocks_from_indent_line"