Bug #15780: Module#const_defined?(String) executes autoloads

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.6.1p33 (2019-01-30 revision 66950) [x86_64-darwin18]
• Backport: 2.4: REQUIRED, 2.5: REQUIRED, 2.6: DONE

[fxn (Xavier Noria)]

The documentation of Module#const_defined? says that autoloads are not executed:

[...] if the constant is not present but there is an autoload for it, true is returned directly without autoloading.

While this seems to work as documented for symbols, constant names passed as strings trigger the autoload:

$ cat x.rb
p X = 1

$ cat foo.rb
Object.autoload("X", "x")
p Object.const_defined?("X")

$ ruby -I. foo.rb
1
true

[Eregon (Benoit Daloze)]

I can confirm the bug. Here is a single-line reproducer:

$ ruby -e 'autoload :X, "foo"; p Object.const_defined?("X")'
Traceback (most recent call last):
	3: from -e:1:in `<main>'
	2: from -e:1:in `const_defined?'
	1: from /home/eregon/.rubies/ruby-2.6.2/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
/home/eregon/.rubies/ruby-2.6.2/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- foo (LoadError)

FWIW, const_defined?("A::B") needs to resolve A to know if it has a B constant, but the last component (B or X) should not trigger any autoload.

[Eregon (Benoit Daloze)]

• Backport changed from 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN to 2.4: REQUIRED, 2.5: REQUIRED, 2.6: REQUIRED

All stable versions have this bug.

[byroot (Jean Boussier)]

I made a patch for this: https://github.com/ruby/ruby/pull/2172

[byroot (Jean Boussier)]

• Status changed from Open to Closed

Applied in changeset git|7d805e67f3275aef066d77aa9c32bef715c362ed.

---

Avoid triggering autoload in Module#const_defined?(String)

[Bug #15780]

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Bug #10741: const_defined? triggers autoload where it did not before added

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.4: REQUIRED, 2.5: REQUIRED, 2.6: REQUIRED to 2.4: REQUIRED, 2.5: REQUIRED, 2.6: DONE

ruby_2_6 r67831 merged revision(s) 7d805e67f3275aef066d77aa9c32bef715c362ed.