Better "dead code" error location

[jez]

Input

→ View on sorbet.run

# typed: true
class A; end
class B1
  if !(self < A)
    raise
  end

  variable = T.unsafe("hello")

  unless variable.nil?
    puts("this is also dead")
  end
end
class B2
  if !(self < A)
    raise
  end

  unless T.unsafe("hello").nil?
    puts("this is also dead")
  end
end

Observed output

editor.rb:8: This code is unreachable https://srb.help/7006
     8 |  variable = T.unsafe("hello")
     9 |
    10 |  unless variable.nil?
    editor.rb:4: This condition was always truthy (T::Boolean)
     4 |  if !(self < A)
             ^^^^^^^^^^^
  Got T::Boolean originating from:
    editor.rb:4:
     4 |  if !(self < A)
             ^^^^^^^^^^^

editor.rb:19: This code is unreachable https://srb.help/7006
    19 |  unless T.unsafe("hello").nil?
                 ^^^^^^^^^^^^^^^^^^^^^^
    editor.rb:15: This condition was always truthy (T::Boolean)
    15 |  if !(self < A)
             ^^^^^^^^^^^
  Got T::Boolean originating from:
    editor.rb:15:
    15 |  if !(self < A)
             ^^^^^^^^^^^
Errors: 2

Expected behavior

In #4483, we made some changes to both tweak the error location for "This code is unreachable" errors so that it would span all the dead code in a dead block from the first dead instruction to the end of the block. That doesn't quite go far enough: it would be nice to have the error expand all the way to any downstream blocks.

This particular error code powers Sorbet's support for the LSP "Unnecessary" diagnostic tag, which instructs LSP clients to dim or gray out the unnecessary code if they wish. Since the error diagnostic stops short of highlighting all the dead code, the IDE won't highlight all the dead code.

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