From: jared@...
Date: 2014-07-20T02:52:01+00:00
Subject: [ruby-core:63889] [ruby-trunk - Bug #9931] irb: Really weird behavior for x = "#{x\"}" (ex: irb(main:009:-4))

Issue #9931 has been updated by Jared Beck.


Interesting.  Let's try to figure it out!

## The irb prompt 

The prompt has two numbers.  The first is obviously a line number, but what is the second number?

    irb(main):001:0> "#{
    irb(main):002:0> end
    irb(main):003:-1> end
    irb(main):004:-2> do
    irb(main):005:-1> do
    irb(main):006:0> }"
    SyntaxError: (irb):2: syntax error, unexpected keyword_end
    (irb):6: unterminated string meets end of file
      from /Users/jared/.rbenv/versions/2.1.2/bin/irb:11:in `<main>'

The second number seems to be a simple estimate of block depth.  It must be implemented very simply, if it is capable of being negative.

## String interpolation is a block

    irb(main):013:0> "#{
    irb(main):014:0>   [1, 2, 3].map { |x| x * 2 }
    irb(main):015:0" }"
    => "[2, 4, 6]"

It's just a block!  We can put whatever we want in there. :)

Note that on the third line, the prompt character changed from `>` to `"`, indicating (roughly) that `irb` thinks we're inside a string.

## The syntax error

In the given example

    "#{x\"}"

the string is closed at col. 5.  The contents of the string are:

    #{x\

We can see that the interpolation block was not closed.  So, the syntax error

    expecting '}'

makes sense.

----------------------------------------
Bug #9931: irb: Really weird behavior for x = "#{x\"}" (ex: irb(main:009:-4))
https://bugs.ruby-lang.org/issues/9931#change-47916

* Author: Jesse Adkins
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 1.9.3p484 (2013-11-22 revision 43786) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
----------------------------------------
# Our journey starts off rather simple:
irb(main):001:0> x = "#{x}"
=> ""
# Okay, makes sense.
irb(main):002:0> x = "#{x\"}"
irb(main):003:0" 
# Hmm...Still in a string? That's weird.
irb(main):003:0" "
irb(main):004:0> 
# Things seem back to normal but...
irb(main):004:0> x
# Nothing? But x is defined!
irb(main):005:0> 
# Nothing? Hmm...
irb(main):005:0> end
irb(main):006:-1> end
# Uhh...I don't think that's supposed to do that.
irb(main):007:-2> end
irb(main):008:-3> end
irb(main):009:-4> 
# ...I'm afraid to go deeper.
# Get me out of here!
irb(main):009:-4> quit
irb(main):010:-4> 
# O.O
irb(main):010:-4> ^C
irb(main):010:0> 
# ...Can I go now?
irb(main):010:0> quit
# Success!

# Additionally, if I put this in a file:
x = "#{x\"}"

# I get two syntax errors (ruby 1.9.3):
test.rb:1: syntax error, unexpected $undefined, expecting '}'
x = "#{x\"}"
         ^
test.rb:1: syntax error, unexpected $end, expecting '}'
x = "#{x\"}"
            ^




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