Incorrect output with a reused argument matcher

[pirj]

Subject of the issue

RSpec.describe 'A', :aggregate_failures do
  specify do
    matcher = contain_exactly(eq(1))

    expect([2]).to matcher
    expect([3]).to matcher
  end
end

The second failure message seems to have traces from the first evaluation:

            the extra elements were:        [2]

It appears that with_matchers_cloned (lib/rspec/matchers/composable.rb) doesn't cover this case.

Adding .clone or .dup to .to matcher solves the issue.

Your environment

• Ruby version: 2.7.1
• RSpec 3.10
  • rspec-core 3.10.1
  • rspec-expectations 3.10.1

Expected behavior

  1) A is expected to contain exactly (eq 1)
     Got 2 failures:

     1.1) Failure/Error: expect([2]).to matcher.dup

            expected collection contained:  [(eq 1)]
            actual collection contained:    [2]
            the missing elements were:      [(eq 1)]
            the extra elements were:        [2]
          # ./spec/a_spec.rb:5:in `block (2 levels) in <top (required)>'

     1.2) Failure/Error: expect([3]).to matcher.dup

            expected collection contained:  [(eq 1)]
            actual collection contained:    [3]
            the missing elements were:      [(eq 1)]
            the extra elements were:        [3]
          # ./spec/a_spec.rb:6:in `block (2 levels) in <top (required)>'

Actual behavior

  1) A is expected to contain exactly (eq 1)
     Got 2 failures:

     1.1) Failure/Error: expect([2]).to matcher

            expected collection contained:  [(eq 1)]
            actual collection contained:    [2]
            the missing elements were:      [(eq 1)]
            the extra elements were:        [2]
          # ./spec/a_spec.rb:5:in `block (2 levels) in <top (required)>'

     1.2) Failure/Error: expect([3]).to matcher

            expected collection contained:  [(eq 1)]
            actual collection contained:    [3]
            the missing elements were:      [(eq 1)]
            the extra elements were:        [2]
          # ./spec/a_spec.rb:6:in `block (2 levels) in <top (required)>'

[JonRowe]

Some output must be cached between runs, we are supposed to be allowing this use case.

[pirj]

Fixed in #1326