From: "kddnewton (Kevin Newton) via ruby-core" <ruby-core@...>
Date: 2024-05-03T13:43:28+00:00
Subject: [ruby-core:117759] [Ruby master Bug#20467] Prism creates a wrong ConstantReadNode for `Bar::Foo = 42`

Issue #20467 has been updated by kddnewton (Kevin Newton).


I've changed it to be the following since https://github.com/ruby/ruby/pull/10716.

```
irb(main):001> Prism.parse(%q(Bar::Foo)).value
=> 
@ ProgramNode (location: (1,0)-(1,8))
��������� locals: []
��������� statements:
    @ StatementsNode (location: (1,0)-(1,8))
    ��������� body: (length: 1)
        ��������� @ ConstantPathNode (location: (1,0)-(1,8))
            ��������� parent:
            ���   @ ConstantReadNode (location: (1,0)-(1,3))
            ���   ��������� name: :Bar
            ��������� name: :Foo
            ��������� delimiter_loc: (1,3)-(1,5) = "::"
            ��������� name_loc: (1,5)-(1,8) = "Foo"
```

----------------------------------------
Bug #20467: Prism creates a wrong ConstantReadNode for `Bar::Foo = 42`
https://bugs.ruby-lang.org/issues/20467#change-108167

* Author: mame (Yusuke Endoh)
* Status: Open
* Assignee: kddnewton (Kevin Newton)
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
Currently, Prism creates the following AST for `Bar::Foo = 42`

```
irb(main):001> Prism.parse(%q(Bar::Foo = 42)).value
=>
@ ProgramNode (location: (1,0)-(1,13))
��������� locals: []
��������� statements:
    @ StatementsNode (location: (1,0)-(1,13))
    ��������� body: (length: 1)
        ��������� @ ConstantPathWriteNode (location: (1,0)-(1,13))
            ��������� target:
            ���   @ ConstantPathNode (location: (1,0)-(1,8))
            ���   ��������� parent:
            ���   ���   @ ConstantReadNode (location: (1,0)-(1,3))
            ���   ���   ��������� name: :Bar
            ���   ��������� child:
            ���   ���   @ ConstantReadNode (location: (1,5)-(1,8))
            ���   ���   ��������� name: :Foo
            ���   ��������� delimiter_loc: (1,3)-(1,5) = "::"
            ��������� operator_loc: (1,9)-(1,10) = "="
            ��������� value:
                @ IntegerNode (location: (1,11)-(1,13))
                ��������� flags: decimal
                ��������� value: 42
```

Note that it includes `ConstantReadNode(name: :Foo)`. I believe this is a bug because `Bar::Foo = 42` does not read a constant `Foo`.

Also, `Foo` and `Bar::Foo` generates the followings. 

```
irb(main):002> Prism.parse(%q(Foo)).value
=>
@ ProgramNode (location: (1,0)-(1,3))
��������� locals: []
��������� statements:
    @ StatementsNode (location: (1,0)-(1,3))
    ��������� body: (length: 1)
        ��������� @ ConstantReadNode (location: (1,0)-(1,3))
            ��������� name: :Foo
irb(main):003> Prism.parse(%q(Bar::Foo)).value
=>
@ ProgramNode (location: (1,0)-(1,8))
��������� locals: []
��������� statements:
    @ StatementsNode (location: (1,0)-(1,8))
    ��������� body: (length: 1)
        ��������� @ ConstantPathNode (location: (1,0)-(1,8))
            ��������� parent:
            ���   @ ConstantReadNode (location: (1,0)-(1,3))
            ���   ��������� name: :Bar
            ��������� child:
            ���   @ ConstantReadNode (location: (1,5)-(1,8))
            ���   ��������� name: :Foo
            ��������� delimiter_loc: (1,3)-(1,5) = "::"
```

Note that both have the same subtree of `ConstantReadNode(name: :Foo)`. It is very confusing because `Foo` (non-scoped read of `Foo`) and `Bar::Foo` (scoped read of `Foo`) have very different meanings.

I think the following design would be desirable.

```
# Foo::Bar=42

ConstantPathWriteNode(
  base: ConstantReadNode(name: ConstantNameNode(:Foo)),
  name: ConstantNameNode(:Bar),
  value: 42
)

# Foo

ConstantReadNode(name: ConstantNameNode(:Foo))

# Foo::Bar

ConstantPathReadNode(
  base: ConstantReadNode(name: ConstantNameNode(:Foo)),
  name: ConstantNameNode(:Bar),
)
```




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