Object.const_defined? not respecting namespace check.

[HoneyryderChuck]

Environment Information

• JRuby version: "jruby 10.0.0.1 (3.4.2) 2025-05-07 79cf1e4aec OpenJDK 64-Bit Server VM 24.0.1+9-30 on 24.0.1+9-30 +indy +jit [x86_64-darwin]"
• Operating system and platform: Darwin MacBook-Pro.local 24.5.0 Darwin Kernel Version 24.5.0: Tue Apr 22 19:53:26 PDT 2025; root:xnu-11417.121.6~2/RELEASE_X86_64 x86_64

Expected Behavior

Given the following snippet, I'd expect the const not to be defined:

Object.const_set :Bang, Module.new
Object.const_defined?("Bang::Struct") #=>should be false

Actual Behavior

The snippet above returns true in jruby 10.0.0.1, false in cruby.

[HoneyryderChuck]

Funnily enough, the same happens in truffleruby.

[headius]

Nice find!

[enebo]

This also happens in JRuby 9.4 and I suspect earlier versions.

[enebo]

So the gist of what is wrong is that this sets search Object internally so it finds things defined on Object:

Object.const_set :Bang, Module.new; p Object.const_defined?("Bang::String")