Ruby 2.7: Beginless ranges fully supported

[LillianZ]

Finishing up from #2155

In this PR, added support for:
Range#{cover?, include?, ===}.
String#{byteslice, slice, slice!} and Symbol#slice
Kernel#{caller, caller_locations} and Thread#backtrace_locations

Shopify#1

[eregon]

I'll let @norswap review the rest.

[norswap]

Looks good. Great work on all these new specs 👍

[norswap]

Same as cover_range?, hard to follow because of the existing code.

Proposal (completely untested):

def self.cover?(range, value)
  # Check lower bound.
  if !Primitive.nil?(range.begin)
    # MRI uses <=> to compare, so must we.
    cmp = (range.begin <=> value)
    return false if Compare.compare_int(cmp) > 0
  end

  # Check upper bound.
  if !Primitive.nil(range.end)
    value = value + (range.exclude_end? 1 : 0)
    cmp = (value <=> range.end)
    return false if Comparable.compare_int(cmp) > 0
  end

  true
end

[LillianZ]

Also much more beautiful, thanks!

Also, r_less is no longer being used, so I commented it out; not sure if it should be removed altogether.

[eregon]

Yes, let's remove range_less if it's unused :)
(we can always use the git history to restore it if it's useful in the future)

[norswap]

Seems good to go for me, unless there are more changes that need to go in?

[LillianZ]

I'm done and ready to merge. Thank you for the great suggestions!

[chrisseaton]

Great PR to finish a tricky set of specs!

[eregon]

There has some CI failures, I'm not sure why GitHub Actions didn't run on the last changes.
In MRI tests (same in some specs):

  1) Failure:
Bug::Test_ExceptionAT#test_exception_at_throwing [/b/b/e/main/test/mri/tests/cext-ruby/exception/test_exception_at_throwing.rb:7]:
assert_separately failed with error message
pid 22634 exit 0
| resource:/truffleruby/core/truffle/range_operations.rb:93: warning: `-' after local variable or literal is interpreted as binary operator
| resource:/truffleruby/core/truffle/range_operations.rb:93: warning: even though it seems like unary operator


  2) Failure:
OpenSSL::TestEngine#test_engines_free [/b/b/e/main/test/mri/tests/openssl/test_engine.rb:76]:
assert_separately failed with error message
pid 22838 exit 0
| resource:/truffleruby/core/truffle/range_operations.rb:93: warning: `-' after local variable or literal is interpreted as binary operator
| resource:/truffleruby/core/truffle/range_operations.rb:93: warning: even though it seems like unary operator

Lint:

Offenses:

src/main/ruby/truffleruby/core/truffle/range_operations.rb:85:68: C: Layout/TrailingWhitespace: Trailing whitespace detected.
      return false unless (Primitive.nil?(b2) || cover?(range, b2)) 
                                                                   ^

[LillianZ]

Thanks for letting me know, I think it's fixed now!

The non-running tests could have something to do with the fact the CHANGELOG is conflicting? In the future I'll wait until after the reviews to write it.

[eregon]

The non-running tests could have something to do with the fact the CHANGELOG is conflicting?

That seems likely, I didn't think about it.
Something worth mentioning in that GitHub issue about an incorrectly-reported conflict, cc @chrisseaton

A workaround would be to rebase the PR, but we'll try first if this now passes the internal CI.