[Fix #9373]Fix indentation style tabs infinite loop

[joeyparis]

This fixes the bug described in #9373.

However, the testing for this cop breaks as it designed to replace every 2 spaces, with 1 tab but the fix replaces every 1 space with 1 tab. I would say this is a problem with the fix, but replacing 2 spaces only works in the vacuum of the test and leads to an infinite loop when used along with other cops.

When combined with Layout/IndentationWidth replacing every 1 space with a tab still leads to proper indentation by the time all the cops are done. But I'm assuming this is not ideal behavior for one to have to rely on another like that.

I'm not sure what the proper steps are to finalize this. Do I update the tests to just replace every 1 space with 1 tab? Or should we dive deeper into what else is contributing to the infinite loop?

---

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[bbatsov]

@jonas054 Please, take a look here when you can.

[jonas054]

There are two distinct ways of using tab characters for indentation.

1. Use tabs with a width of 4 or 8 to save characters in a source code file. Tabs can be followed by spaces to reach the desired indentation level. There's no support in RuboCop for this way. For example,

class MyClass
  def my_method
    @list.each do
      if x
< tab  >unless y
< tab  >  puts 'Yes'
< tab  >end
      end
    end
end

2. Use tab for indentation, no spaces, and necessarily one tab for one level of indentation. This is possible with RuboCop.

class MyClass
<>def my_method
<><>@list.each do
<><><>if x
<><><><>unless y
<><><><><>puts 'Yes'
<><><><>end
<><><>end
<><>end
end

Using more than one tab per indentation level makes no sense. I think that adding validation so that Layout/IndentationWidth must be set to 1 if EnforcedStyle is tabsin Layout/IndentationStyle would solve the problem.

We should also change the comment # Number of spaces for each indentation level in default.yml to # Number of spaces or tabs for each indentation level.

[jonas054]

I think validating configuration is the way to go, rather than changing the autocorrect behavior. See comment.

[PikachuEXE]

Seems incompatible with cop Layout/DotPosition when EnforcedStyle: trailing

[jonas054]

@PikachuEXE I'm not so sure that trailing dot position as any different than leading. The alignment with the first line for the chained method calls is just not possible when tabs are used for indentation.

For example, default configuration with spaces gives:

unless y
       .z
  puts 'Yes'
end

while the configuration

Layout/IndentationWidth:
  Width: 1

Layout/IndentationStyle:
  EnforcedStyle: tabs

results in:

unless y
<><><><><><><>.z
<>puts 'Yes'
end

and with the addition of

Layout/DotPosition:
  EnforcedStyle: trailing

we get

unless y.
<><><><><><><>z
<>puts 'Yes'
end

The problem remains the same. Many cops that deal with alignment don't work well with tabs, and many times it's a problem that can't be solved unless we mix tabs and spaces, and then what's the point of using tabs?