[formatter] Index out of bounds (IndexError) When run formatter

[zw963]

Bug Report

Probably related to #15242

When try to format following code:

module Procodile
  class Supervisor
    def check_concurrency(
      options : Supervisor::Options = Supervisor::Options.new
    ) : Hash(Symbol, Array(Instance))
      if result[:started].present?
        Procodile.log nil, "system", "Concurrency check started \
#{result[:started].map(&.description).join(", ")}"
      end
    end

    def to_hash : NamedTuple(started_at: Int64?, pid: Int64)
      started_at = @started_at

      {
        started_at: started_at ? started_at.to_unix : nil,
        pid:        ::Process.pid,
      }
    end
  end
end

get error like following:

 ╰──➤ $ 1  crystal tool format --show-backtrace test.cr
Index out of bounds (IndexError)
  from /crystal/src/indexable.cr:977:29 in '[]'
  from /crystal/src/compiler/crystal/tools/formatter.cr:5042:15 in 'align_info'
  from /crystal/src/compiler/crystal/tools/formatter.cr:4999:11 in 'align_infos'
  from /crystal/src/compiler/crystal/tools/formatter.cr:4948:7 in 'finish'
  from /crystal/src/compiler/crystal/tools/formatter.cr:23:7 in 'format_source'
  from /crystal/src/compiler/crystal/command/format.cr:133:7 in 'format_many'
  from /crystal/src/compiler/crystal/command/format.cr:63:5 in 'format'
  from /crystal/src/reference.cr:75:3 in 'tool'
  from /crystal/src/compiler/crystal/command.cr:118:7 in 'run'
  from /crystal/src/compiler/crystal.cr:11:1 in '__crystal_main'
  from /crystal/src/crystal/main.cr:118:5 in 'main'
  from src/env/__libc_start_main.c:95:2 in 'libc_start_main_stage2'

The issue caused by

        Procodile.log nil, "system", "Concurrency check started \
#{result[:started].map(&.description).join(", ")}"

If change to following one-line version, issue is not happen.

        Procodile.log nil, "system", "Concurrency check started #{result[:started].map(&.description).join(", ")}"

---

But, if remove the to_hash method, this issue not happen too.

# no error

module Procodile
  class Supervisor
    def check_concurrency(
      options : Supervisor::Options = Supervisor::Options.new
    ) : Hash(Symbol, Array(Instance))
      if result[:started].present?
        Procodile.log nil, "system", "Concurrency check started \
#{result[:started].map(&.description).join(", ")}"
      end
    end
  end
end