Prism.find can return the wrong node on older Ruby versions

[eregon]

Quoting from https://bugs.ruby-lang.org/issues/21795#note-13:

---

I thought more about node_id and I found at least one case where it is problematic with different versions of Prism.
The problem is the node_id from the bytecode is computed by the builtin Prism parser used by prism_compile.c, while the usage of e.g. Prism.find might use a more recent Prism.
Here is a reproduction showing the problem:

if false
  # A code snippet which generates a different number of nodes on Prism 1.2.0 and 1.9.0
  case 1
  in 2
    A.print message:
  in 3
    A.print message:
  end
end

def a
end

def b
end

require "prism"
p Prism.find(method(:b))

ruby master is fine:

$ ruby -v find_check.rb
ruby 4.1.0dev (2026-03-27T16:16:27Z revert-source_loca.. f510d4103e) +PRISM [x86_64-linux]
@ DefNode (location: (14,0)-(15,3))
├── flags: newline
├── name: :b

But on Ruby 3.4.5 it's broken:

# Use latest prism, there is no prism release with Prism.find yet:
$ cd prism
$ bundle exec rake compile
$ bundle exec ruby find_check.rb 
@ DefNode (location: (11,0)-(12,3))
├── flags: newline
├── name: :a

This returns method a and not b!

And if I change p Prism.find(method(:b)) to p Prism.find(method(:a)),
then ruby-master is correct, but 3.4.5 returns an IfNode.

IOW, 3.4.5 returns the wrong node

---

I think a good fix for now would be to remove the RubyVM-based implementation of Node.find.
And use start/end offset (or line+column) when that becomes available.

[eregon]

For posterity here is how I found such cases.

Ruby < 3.4.2 reports node_id: -1 from the bytecode, so RubyVM does not work there.
So I'm using Ruby 3.4.2:

Dir.glob("test/prism/fixtures/**/*.txt") do |file|
  next if file =~ /fixtures\/[34]\./
  # puts file

  prism120 = `/home/eregon/.rubies/ruby-3.4.2/bin/ruby -rprism -e 'r=Prism.parse_file(#{file.dump}); p r.value.node_id'`.chomp
  prism190 = `/home/eregon/.rubies/ruby-master/bin/ruby -rprism -e 'r=Prism.parse_file(#{file.dump}); p r.value.node_id'`.chomp
  if prism120 != prism190
    puts "Difference on #{file}: #{prism120} vs #{prism190}"
  end
end

$ ruby find_diff_node_id.rb
Difference on test/prism/fixtures/case_in_hash_key.txt: 25 vs 26
Difference on test/prism/fixtures/defined.txt: 30 vs 25
Difference on test/prism/fixtures/endless_methods.txt: 35 vs 36
ruby: prism/util/pm_newline_list.c:51: pm_newline_list_append: Assertion `list->size == 0 || newline_offset > list->offsets[list->size - 1]' failed.
Difference on test/prism/fixtures/heredoc_percent_q_newline_delimiter.txt:  vs 24
Difference on test/prism/fixtures/it_assignment.txt: 13 vs 12
Difference on test/prism/fixtures/spanning_heredoc.txt: 73 vs 76

[Earlopain]

I don't have much to add but the implementation also supports Thread::Backtrace::Location which only contains a line number. They don't return the same info:

require "prism"

def foo(...)
end


begin
  foo(-> { raise }.call)
rescue => e
  pp Prism.find(e.backtrace_locations[0], rubyvm: true) # CallNode (raise)
  pp Prism.find(e.backtrace_locations[0], rubyvm: false) # StatementsNode (foo)
end

Under the hood it uses node_id_for_backtrace_location and otherwise it just gets the first node that matches the backtrace location line number.