Import some CodeHelpers from Pry.

The hope is that they can live in this gem permanently, and Pry can also
include MethodSource::CodeHelpers in the relevant places.

1 files changed, 125 insertions, 0 deletions

diff --git a/lib/method_source/code_helpers.rb b/lib/method_source/code_helpers.rb
new file mode 100644
index 0000000..173609e
--- /dev/null
+++ b/lib/method_source/code_helpers.rb
@@ -0,0 +1,125 @@
+module MethodSource
+
+  module CodeHelpers
+    # Retrieve the first expression starting on the given line of the given file.
+    #
+    # This is useful to get module or method source code.
+    #
+    # @param [Array<String>, File, String] file  The file to parse, either as a File or as
+    # @param [Fixnum]  line_number  The line number at which to look.
+    #                             NOTE: The first line in a file is line 1!
+    # @param [Boolean]  strict  If set to true, then only completely valid expressions are
+    #                         returned. Otherwise heuristics are used to extract
+    #                         expressions that may have been valid inside an eval.
+    # @return [String]  The first complete expression
+    # @raise [SyntaxError]  If the first complete expression can't be identified
+    def expression_at(file, line_number, strict=false)
+      lines = file.is_a?(Array) ? file : file.each_line.to_a
+
+      relevant_lines = lines[(line_number - 1)..-1] || []
+
+      extract_first_expression(relevant_lines)
+    rescue SyntaxError => e
+      raise if strict
+
+      begin
+        extract_first_expression(relevant_lines) do |code|
+          code.gsub(/\#\{.*?\}/, "temp")
+        end
+      rescue SyntaxError => e2
+        raise e
+      end
+    end
+
+    # Retrieve the comment describing the expression on the given line of the given file.
+    #
+    # This is useful to get module or method documentation.
+    #
+    # @param [Array<String>, File, String] file  The file to parse, either as a File or as
+    #                                            a String or an Array of lines.
+    # @param [Fixnum]  line_number  The line number at which to look.
+    #                             NOTE: The first line in a file is line 1!
+    # @return [String]  The comment
+    def comment_describing(file, line_number)
+      lines = file.is_a?(Array) ? file : file.each_line.to_a
+
+      extract_last_comment(lines[0..(line_number - 2)])
+    end
+
+    # Determine if a string of code is a complete Ruby expression.
+    # @param [String] code The code to validate.
+    # @return [Boolean] Whether or not the code is a complete Ruby expression.
+    # @raise [SyntaxError] Any SyntaxError that does not represent incompleteness.
+    # @example
+    #   complete_expression?("class Hello") #=> false
+    #   complete_expression?("class Hello; end") #=> true
+    #   complete_expression?("class 123") #=> SyntaxError: unexpected tINTEGER
+    def complete_expression?(str)
+      old_verbose = $VERBOSE
+      $VERBOSE = nil
+
+      catch(:valid) do
+        eval("BEGIN{throw :valid}\n#{str}")
+      end
+
+      # Assert that a line which ends with a , or \ is incomplete.
+      str !~ /[,\\]\s*\z/
+    rescue IncompleteExpression
+      false
+    ensure
+      $VERBOSE = old_verbose
+    end
+
+    private
+
+    # Get the first expression from the input.
+    #
+    # @param [Array<String>]  lines
+    # @param [&Block]  a clean-up function to run before checking for complete_expression
+    # @return [String]  a valid ruby expression
+    # @raise [SyntaxError]
+    def extract_first_expression(lines, &block)
+      code = ""
+      lines.each do |v|
+        code << v
+        return code if complete_expression?(block ? block.call(code) : code)
+      end
+      raise SyntaxError, "unexpected $end"
+    end
+
+    # Get the last comment from the input.
+    #
+    # @param [Array<String>]  lines
+    # @return [String]
+    def extract_last_comment(lines)
+      buffer = ""
+
+      lines.each do |line|
+        # Add any line that is a valid ruby comment,
+        # but clear as soon as we hit a non comment line.
+        if (line =~ /^\s*#/) || (line =~ /^\s*$/)
+          buffer << line.lstrip
+        else
+          buffer.replace("")
+        end
+      end
+
+      buffer
+    end
+
+    # An exception matcher that matches only subsets of SyntaxErrors that can be
+    # fixed by adding more input to the buffer.
+    module IncompleteExpression
+      def self.===(ex)
+        case ex.message
+        when /unexpected (\$end|end-of-file|END_OF_FILE)/, # mri, jruby, ironruby
+          /unterminated (quoted string|string|regexp) meets end of file/, # "quoted string" is ironruby
+          /missing 'end' for/, /: expecting '[})\]]'$/, /can't find string ".*" anywhere before EOF/, /: expecting keyword_end/, /expecting kWHEN/ # rbx
+          true
+        else
+          false
+        end
+      end
+    end
+  end
+end