Issue #13952 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.3: REQUIRED, 2.4: REQUIRED to 2.3: REQUIRED, 2.4: DONE

ruby_2_4 r61455 merged revision(s) 60066.

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Bug #13952: String#succ not updating code range
https://bugs.ruby-lang.org/issues/13952#change-68627

* Author: nirvdrum (Kevin Menard)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-linux]
* Backport: 2.3: REQUIRED, 2.4: DONE
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I'm seeing some strange behavior with `String#succ` and updating code ranges. I haven't yet traced the code to see what the culprit is, but I'm reproducing my findings here so they don't get lost (and maybe someone has a better idea of what's going on.)

This sequence of calls produces the expected output.

```
x = "\xFF".force_encoding("binary")
y = x.succ
z = String.new
z << 0x01 << 0x00

puts "x ASCII-only?: #{x.ascii_only?}"
puts "y ASCII-only?: #{y.ascii_only?}"
puts "z ASCII-only?: #{z.ascii_only?}"
puts "y Encoding: #{y.encoding}"
puts "y Bytes: #{y.bytes}"
puts "z Encoding: #{z.encoding}"
puts "z Bytes: #{z.bytes}"

```

The output is:

```
x ASCII-only?: false
y ASCII-only?: true
z ASCII-only?: true
y Encoding: ASCII-8BIT
y Bytes: [1, 0]
z Encoding: ASCII-8BIT
z Bytes: [1, 0]
```

However, by inserting a call that would force `x` to calculate its code range prior to the `String#succ` call, we get a different set of results:

```
x = "\xFF".force_encoding("binary")
x.ascii_only?
y = x.succ
z = String.new
z << 0x01 << 0x00

puts "x ASCII-only?: #{x.ascii_only?}"
puts "y ASCII-only?: #{y.ascii_only?}"
puts "z ASCII-only?: #{z.ascii_only?}"
puts "y Encoding: #{y.encoding}"
puts "y Bytes: #{y.bytes}"
puts "z Encoding: #{z.encoding}"
puts "z Bytes: #{z.bytes}"
```

Now we see that `y` isn't considered to be ASCII-only, even though it has the exact same encoding and byte sequence as `z` (and as `y` in the previous call sequence that did work):

```
x ASCII-only?: false
y ASCII-only?: false
z ASCII-only?: true
y Encoding: ASCII-8BIT
y Bytes: [1, 0]
z Encoding: ASCII-8BIT
z Bytes: [1, 0]
```

Having not looked at it, it looks like the code range isn't updated and we only get the correct result if `CR_UNKNOWN` hasn't been replaced by some other call that needs the code range.






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