class RSpec::Matchers::BuiltIn::Compound::NestedEvaluator

Normally, we evaluate the matching sequentially. For an expression like ‘expect(x).to foo.and bar`, this becomes:

expect(x).to foo
expect(x).to bar

For block expectations, we need to nest them instead, so that ‘expect { x }.to foo.and bar` becomes:

expect {
  expect { x }.to foo
}.to bar

This is necessary so that the ‘expect` block is only executed once.

Public Class Methods

new(actual, matcher_1, matcher_2) click to toggle source
# File lib/rspec/matchers/built_in/compound.rb, line 157
def initialize(actual, matcher_1, matcher_2)
  @actual        = actual
  @matcher_1     = matcher_1
  @matcher_2     = matcher_2
  @match_results = {}

  inner, outer = order_block_matchers

  @match_results[outer] = outer.matches?(Proc.new do |*args|
    @match_results[inner] = inner.matches?(inner_matcher_block(args))
  end)
end

Private Class Methods

matcher_expects_call_stack_jump?(matcher) click to toggle source
# File lib/rspec/matchers/built_in/compound.rb, line 233
def self.matcher_expects_call_stack_jump?(matcher)
  matcher.expects_call_stack_jump?
rescue NoMethodError
  false
end

Public Instance Methods

matcher_matches?(matcher) click to toggle source
# File lib/rspec/matchers/built_in/compound.rb, line 170
def matcher_matches?(matcher)
  @match_results.fetch(matcher) do
    raise ArgumentError, "Your #{matcher.description} has no match " \
     "results, this can occur when an unexpected call stack or " \
     "local jump occurs. Prehaps one of your matchers needs to " \
     "declare `expects_call_stack_jump?` as `true`?"
  end
end

Private Instance Methods

inner_matcher_block(outer_args) click to toggle source

Some block matchers (such as ‘yield_xyz`) pass args to the `expect` block. When such a matcher is used as the outer matcher, we need to forward the the args on to the `expect` block.

# File lib/rspec/matchers/built_in/compound.rb, line 184
def inner_matcher_block(outer_args)
  return @actual if outer_args.empty?

  Proc.new do |*inner_args|
    unless inner_args.empty?
      raise ArgumentError, "(#{@matcher_1.description}) and " \
        "(#{@matcher_2.description}) cannot be combined in a compound expectation " \
        "since both matchers pass arguments to the block."
    end

    @actual.call(*outer_args)
  end
end
order_block_matchers() click to toggle source

For a matcher like ‘raise_error` or `throw_symbol`, where the block will jump up the call stack, we need to order things so that it is the inner matcher. For example, we need it to be this:

expect {
  expect {
    x += 1
    raise "boom"
  }.to raise_error("boom")
}.to change { x }.by(1)

…rather than:

expect {
  expect {
    x += 1
    raise "boom"
  }.to change { x }.by(1)
}.to raise_error("boom")

In the latter case, the after-block logic in the ‘change` matcher would never get executed because the `raise “boom”` line would jump to the `rescue` in the `raise_error` logic, so only the former case will work properly.

This method figures out which matcher should be the inner matcher and which should be the outer matcher.

# File lib/rspec/matchers/built_in/compound.rb, line 224
def order_block_matchers
  return @matcher_1, @matcher_2 unless self.class.matcher_expects_call_stack_jump?(@matcher_2)
  return @matcher_2, @matcher_1 unless self.class.matcher_expects_call_stack_jump?(@matcher_1)

  raise ArgumentError, "(#{@matcher_1.description}) and " \
    "(#{@matcher_2.description}) cannot be combined in a compound expectation " \
    "because they both expect a call stack jump."
end