Multiline method call with block raises MethodSource::SourceNotFoundError

[dleavitt]

Related to #22

For blocks, source_location reports the line where the block opens as its line number. If the block is part of a multiline expression, this can be partway through the expression.

Maybe expression_at needs to start looking backwards (at line numbers prior to the provided one) if the first line has a syntax error?

class A
  attr_reader :blk

  def initialize(_stuff, &blk)
    @blk = blk
  end
end

a = A.new("a" => 1, "b" => 2) do
  "Block!"
end

b = A.new("a" => 1,
          "b" => 2) do # line 14
  "Block!"
end

puts a.blk.source #=> works
puts b.blk.source_location #=> a.rb 14
puts b.blk.source #=> MethodSource::SourceNotFoundError

MethodSource::SourceNotFoundError: Could not parse source for #<Proc:0x00007f85ebcb34a0 ~/a.rb:14>: (eval):2: syntax error, unexpected =>, expecting end-of-input
          "b" => 2) do
              ^~

from ~/.rbenv/versions/2.7.3/lib/ruby/gems/2.7.0/gems/method_source-1.0.0/lib/method_source.rb:29:in `rescue in source_helper'
Caused by SyntaxError: (eval):2: syntax error, unexpected =>, expecting end-of-input
          "b" => 2) do
              ^~

from ~/.rbenv/versions/2.7.3/lib/ruby/gems/2.7.0/gems/method_source-1.0.0/lib/method_source/code_helpers.rb:71:in `eval'