[ruby-core:126327] [Ruby Bug#22235] node_id/location for constant assignment failing while reading

8 Aug 2026

      Issue #22235 has been updated by Eregon (Benoit Daloze).

To be complete, the other two "failing while reading" cases in the spec are:
(`$` marks the beginning and end of the `source_range`)
```ruby
      "index operator assignments failing while reading" => <<-RUBY,
      value = nil
      $value[0] += 42$
      RUBY

      "attribute operator assignments failing while reading" => <<-RUBY,
      value = nil
      $value.foo += 42$
      RUBY
```

Those also currently return the write/assignment node, even though it fails while reading.
We should probably be consistent there and return the "read node" (`value[0]`/`value.foo`).

The trouble there is there isn't such a node in Prism:
1st example, no node with `(3,0)-(3,8)`:
```
$ ruby -rprism -e 'pp Prism.parse("
value = nil
value[0] += 42 
").value' 
@ ProgramNode (location: (2,0)-(3,14))
├── flags: ∅
├── locals: [:value]
└── statements:
    @ StatementsNode (location: (2,0)-(3,14))
    ├── flags: ∅
    └── body: (length: 2)
        ├── @ LocalVariableWriteNode (location: (2,0)-(2,11))
        │   ├── flags: newline
        │   ├── name: :value
        │   ├── depth: 0
        │   ├── name_loc: (2,0)-(2,5) = "value"
        │   ├── value:
        │   │   @ NilNode (location: (2,8)-(2,11))
        │   │   └── flags: static_literal
        │   └── operator_loc: (2,6)-(2,7) = "="
        └── @ IndexOperatorWriteNode (location: (3,0)-(3,14))
            ├── flags: newline
            ├── receiver:
            │   @ LocalVariableReadNode (location: (3,0)-(3,5))
            │   ├── flags: ∅
            │   ├── name: :value
            │   └── depth: 0
            ├── call_operator_loc: ∅
            ├── opening_loc: (3,5)-(3,6) = "["
            ├── arguments:
            │   @ ArgumentsNode (location: (3,6)-(3,7))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ IntegerNode (location: (3,6)-(3,7))
            │           ├── flags: static_literal, decimal
            │           └── value: 0
            ├── closing_loc: (3,7)-(3,8) = "]"
            ├── block: ∅
            ├── binary_operator: :+
            ├── binary_operator_loc: (3,9)-(3,11) = "+="
            └── value:
                @ IntegerNode (location: (3,12)-(3,14))
                ├── flags: static_literal, decimal
                └── value: 42
```

2nd example, no node with `(3,0)-(3,9)`:
```
ruby -rprism -e 'pp Prism.parse("
value = nil
value.foo += 42
").value'
@ ProgramNode (location: (2,0)-(3,15))
├── flags: ∅
├── locals: [:value]
└── statements:
    @ StatementsNode (location: (2,0)-(3,15))
    ├── flags: ∅
    └── body: (length: 2)
        ├── @ LocalVariableWriteNode (location: (2,0)-(2,11))
        │   ├── flags: newline
        │   ├── name: :value
        │   ├── depth: 0
        │   ├── name_loc: (2,0)-(2,5) = "value"
        │   ├── value:
        │   │   @ NilNode (location: (2,8)-(2,11))
        │   │   └── flags: static_literal
        │   └── operator_loc: (2,6)-(2,7) = "="
        └── @ CallOperatorWriteNode (location: (3,0)-(3,15))
            ├── flags: newline
            ├── receiver:
            │   @ LocalVariableReadNode (location: (3,0)-(3,5))
            │   ├── flags: ∅
            │   ├── name: :value
            │   └── depth: 0
            ├── call_operator_loc: (3,5)-(3,6) = "."
            ├── message_loc: (3,6)-(3,9) = "foo"
            ├── read_name: :foo
            ├── write_name: :foo=
            ├── binary_operator: :+
            ├── binary_operator_loc: (3,10)-(3,12) = "+="
            └── value:
                @ IntegerNode (location: (3,13)-(3,15))
                ├── flags: static_literal, decimal
                └── value: 42
```

----------------------------------------
Bug #22235: node_id/location for constant assignment failing while reading
https://bugs.ruby-lang.org/issues/22235#change-118445

* Author: Eregon (Benoit Daloze)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
```ruby
namespace = Module.new
begin
  namespace::NotDefined += 1
rescue => e
  pp e.backtrace_locations[0]
  pp e.backtrace_locations[0].source_range
  pp e.backtrace_locations[0].syntax_tree
end
```

On CRuby master it gives:
```
$ ruby -v const_assignment_fail_while_reading.rb
ruby 4.1.0dev (2026-08-08T08:04:35Z master e56f452e46) +PRISM [x86_64-linux]
"const_assignment_fail_while_reading.rb:3:in '<main>'"
#<Ruby::SourceRange /.../const_assignment_fail_while_reading.rb:(3,2)-(3,28)>
@ ConstantPathOperatorWriteNode (location: (3,2)-(3,28))
├── flags: newline
├── target:
│   @ ConstantPathNode (location: (3,2)-(3,23))
│   ├── flags: ∅
│   ├── parent:
│   │   @ LocalVariableReadNode (location: (3,2)-(3,11))
│   │   ├── flags: ∅
│   │   ├── name: :namespace
│   │   └── depth: 0
│   ├── name: :NotDefined
│   ├── delimiter_loc: (3,11)-(3,13) = "::"
│   └── name_loc: (3,13)-(3,23) = "NotDefined"
├── binary_operator_loc: (3,24)-(3,26) = "+="
├── value:
│   @ IntegerNode (location: (3,27)-(3,28))
│   ├── flags: static_literal, decimal
│   └── value: 1
└── binary_operator: :+
```

So even though it's the read failing, it returns the `ConstantPathOperatorWriteNode` and the section is `namespace::NotDefined += 1`.

I'm implementing `source_range` & `syntax_tree` on TruffleRuby and there the result is:
```
"const_assignment_fail_while_reading.rb:3:in 'Module#const_missing'"
#<Ruby::SourceRange /.../const_assignment_fail_while_reading.rb:(3,2)-(3,23)>
@ ConstantPathNode (location: (3,2)-(3,23))
...
```

So this returns the `ConstantPathNode` and the section is `namespace::NotDefined`.

I think TruffleRuby is correct here, especially if we want to differentiate failing while reading or writing.
On CRuby it is currently impossible to differentiate because the same node is returned in both cases.
(UPDATE: it's possible to differentiate via the exception, but that seems quite brittle. The point is `syntax_tree`&`source_range` should point to the relevant reading node)

More information:
```
irb(main):001> namespace = Module.new
irb(main):002> namespace::NotDefined += 1
irb(main):003> e=_
irb(main):005> l=e.backtrace_locations[0]
irb(main):008> puts RubyVM::InstructionSequence.of(l).disasm
== disasm: #<ISeq:<compiled>@(irb):2 (2,0)-(2,26)>
0000 getlocal_WC_1                          namespace@0               (   2)[Li]
0002 dup
0003 putobject                              true
0005 getconstant                            :NotDefined
0007 putobject_INT2FIX_1_
0008 opt_plus                               <calldata!mid:+, argc:1, FCALL|ARGS_SIMPLE>[CcCr]
0010 swap
0011 topn                                   1
0013 swap
0014 setconstant                            :NotDefined
0016 leave
irb(main):011> RubyVM::InstructionSequence.of(l).to_a
=> 
["YARVInstructionSequence/SimpleDataFormat",
 4,
 1,
 1,
 {arg_size: 0,
  local_size: 0,
  stack_max: 3,
  node_id: 6,
  source_hash: 614720579064667961,
  code_location: [2, 0, 2, 26],
  node_ids: [2, 5, 5, 5, 4, 5, 5, 5, 5, 5, 6],
  parser: :prism},
 "<compiled>",
 "(irb)",
 nil,
 2,
 :eval,
 [],
 {},
 [],
 [2,
  :RUBY_EVENT_LINE,
  [:getlocal_WC_1, 3],
  [:dup],
  [:putobject, true],
  [:getconstant, :NotDefined],
  [:putobject_INT2FIX_1_],
  [:opt_plus, {mid: :+, flag: 20, orig_argc: 1}],
  [:swap],
  [:topn, 1],
  [:swap],
  [:setconstant, :NotDefined],
  [:leave]]]
irb(main):013> l.syntax_tree
=> 
@ ConstantPathOperatorWriteNode (location: (1,0)-(1,26))
...
```

The failing instruction must be `getconstant` (BTW, do we have any API to get the insn/insn index for an exception?).
That's given `node_id` 5 which is the `ConstantPathOperatorWriteNode`.

OK to fix the `node_id` of `getconstant` in such a case to point to the `ConstantPathNode`?

-- 
https://bugs.ruby-lang.org/

Eregon (Benoit Daloze)

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