Interpolated variables not enclosed in braces are not noticed

[Sleft]

When you interpolate global, instance or class variables in strings you can omit the enclosing braces. But RuboCop does not notice variables not enclosed in braces and gives a misleading warnings of

Prefer single-quoted strings when you don't need string interpolation or special symbols.

as double-quotation is required for the strings in question.

For example, consider the following code:

# -*- coding: utf-8 -*-

class Klass
  def meth
    @bar = @@bar = $bar = 'baz'
    puts "foo#@bar"
    puts "foo#@@bar"
    puts "foo#$bar"
  end
end

When inspecting this rubocop says

C:  5: Replace class var @@bar with a class instance var.
C:  6: Prefer single-quoted strings when you don't need string interpolation or special symbols.
C:  7: Prefer single-quoted strings when you don't need string interpolation or special symbols.
C:  7: Replace class var @@bar with a class instance var.
C:  8: Prefer single-quoted strings when you don't need string interpolation or special symbols.

But replacing the strings with single-quoted ones will not allow for interpolation.

[bbatsov]

This certainly is a bug, that we'll address soon. On a related note - interpolating variables like this is considered bad style(it's a remnant of the ancient Ruby history), so we should add a check for this as well.

[bbatsov]

@jonas054 Here's where the problem with the existing check lies:

[3] pry(main)> Ripper.lex('puts "test#@@top"')
=> [[[1, 0], :on_ident, "puts"],
 [[1, 4], :on_sp, " "],
 [[1, 5], :on_tstring_beg, "\""],
 [[1, 6], :on_tstring_content, "test"],
 [[1, 10], :on_embvar, "#"],
 [[1, 11], :on_cvar, "@@top"],
 [[1, 16], :on_tstring_end, "\""]]
[4] pry(main)> Ripper.lex('puts "test#{@@top}"')
=> [[[1, 0], :on_ident, "puts"],
 [[1, 4], :on_sp, " "],
 [[1, 5], :on_tstring_beg, "\""],
 [[1, 6], :on_tstring_content, "test"],
 [[1, 10], :on_embexpr_beg, "\#{"],
 [[1, 12], :on_cvar, "@@top"],
 [[1, 17], :on_embexpr_end, "}"],
 [[1, 18], :on_tstring_end, "\""]]

The code in StringLiterals currently checks only for :on_embexpr_beg.

[jonas054]

Thanks, I'll try to solve it tonight.

[bbatsov]

That won't be needed - I got a bit of an inspiration and fixed it myself :-) I've also implemented a cop to warn against the use of interpolated variables.

[jonas054]

Great!