[ruby-core:103726] [Ruby master Bug#15928] Constant declaration does not conform to JIS 3017:2013

Issue #15928 has been updated by jeremyevans0 (Jeremy Evans).


Eregon (Benoit Daloze) wrote in #note-5:
> No, the spec should be kept for older versions/other implementations, and we should have a spec for the new behavior.

If the behavior was a deliberate feature in older versions, I agree.  If the behavior was not deliberate in old versions, and changing it is just fixing a bug (as it is in this case), I disagree.  Simply because it took a long time for this bug to be fixed does not mean it should be treated differently from other bugs.

I believe all bug fixes that break specs should be treated this way (removing broken specs), and all features implemented that break specs be handled by adding appropriate version guards to existing specs.  In either case, it's fine but not required to add specs with appropriate version guards.

----------------------------------------
Bug #15928: Constant declaration does not conform to JIS 3017:2013
https://bugs.ruby-lang.org/issues/15928#change-91821

* Author: yugui (Yuki Sonoda)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.0dev (2019-06-16T14:01:46Z master d4929f5185) [x86_64-darwin18]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
The order of evaluation in constant declaration does not conform to JIS 3017:2013 11.4.2.2.3.

# Problem

Suppose that we are evaluating the following program.

```
expr::C = lhs
```

The standard seems to be requiring the following evaluation order:

1. expr
  * raise a TypeError if the value is not a kind of Module
2. lhs
3. rb_const_set(expr, :C, lhs)

However, the actual implementation evaluates in the following order

1. lhs
2. expr
3. rb_const_set(expr, :C, lhs)
  * raise a TypeError if the expr is not a kind of Module


# How to reproduce

The next program does not raise "recv" but raises "value"

```
raise("recv")::C = raise("value")
```

The next program does not raise a TypeError but raises a RuntimeError

```
A = 1
A::C = raise("value")
```

# Question
* Is this interpretation of the standard correct?
* If it is, Should we change the current behavior?
* If we shouldn't, does it mean an issue in the standard?

c.f.
* https://twitter.com/n0kada/status/1140234416175763456



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