[ruby-core:121683] [Ruby Bug#21272] Class.new doesn't trigger :class TracePoint

[ruby-core:121683] [Ruby Bug#21272] Class.new doesn't trigger :class TracePoint

[st0012 (Stan Lo) via ruby-core]

Issue #21272 has been reported by st0012 (Stan Lo).

----------------------------------------
Bug #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272

* Author: st0012 (Stan Lo)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




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[ruby-core:121738] [Ruby Bug#21272] Class.new doesn't trigger :class TracePoint

[Eregon (Benoit Daloze) via ruby-core]

Issue #21272 has been updated by Eregon (Benoit Daloze).


In my view, `Baz = Class.new` doesn't really "Start a class or module definition." it creates a class but there is no definition of it, no body.
Though `Baz = Class.new { ... }` would arguably start a definition/body, but then so would `Baz.class_exec { ... }` and that seems less reasonable to catch with a :class TracePoint.

I think unless there is a good motivating example to change behavior (which could be incompatible), it's better to just document it better, so I'd suggest opening a PR to document it better.

----------------------------------------
Bug #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-112793

* Author: st0012 (Stan Lo)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




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[ruby-core:124713] [Ruby Bug#21272] Class.new doesn't trigger :class TracePoint

[cfis (Charlie Savage) via ruby-core]

Issue #21272 has been updated by cfis (Charlie Savage).


This is a difference in Ruby 4.0, all previous versions of Ruby send out a Class.new event. You can see this in the ruby-prof test suite which now has lots of new failures. For example this test now fails:




----------------------------------------
Bug #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116309

* Author: st0012 (Stan Lo)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




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[ruby-core:124715] [Ruby Bug#21272] Class.new doesn't trigger :class TracePoint

[Eregon (Benoit Daloze) via ruby-core]

Issue #21272 has been updated by Eregon (Benoit Daloze).


cfis (Charlie Savage) wrote in #note-2:
> This is a difference in Ruby 4.0. Previous versions of Ruby sent out a Class.new event.

No they did not as far as I can see. Even Ruby 2.0.0 does not emit a `:class` tracepoint for `Class.new`:
```
$ ruby -ve 'TracePoint.trace(:class) { puts "class tp" }; p 1; class Foo; end; p 2; Class.new {}'
ruby 2.0.0p648 (2015-12-16 revision 53162) [x86_64-linux]
1
class tp
2
$ ruby -ve 'TracePoint.trace(:class) { puts "class tp" }; p 1; class Foo; end; p 2; Class.new {}'
ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [x86_64-linux]
1
class tp
2
```

----------------------------------------
Bug #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116311

* Author: st0012 (Stan Lo)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




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[ruby-core:124716] [Ruby Feature#21272] Class.new doesn't trigger :class TracePoint

[Eregon (Benoit Daloze) via ruby-core]

Issue #21272 has been updated by Eregon (Benoit Daloze).

Tracker changed from Bug to Feature
Backport deleted (3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN)

Changing this to a feature request.

----------------------------------------
Feature #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116312

* Author: st0012 (Stan Lo)
* Status: Open
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




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[ruby-core:124717] [Ruby Feature#21272] Class.new doesn't trigger :class TracePoint

[Eregon (Benoit Daloze) via ruby-core]

Issue #21272 has been updated by Eregon (Benoit Daloze).


@cfis I think you're thinking about `:call` TracePoints, that's unrelated to this issue and that did change in 4.0, see #21254 and #21298.

----------------------------------------
Feature #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116313

* Author: st0012 (Stan Lo)
* Status: Open
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




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[ruby-core:124722] [Ruby Feature#21272] Class.new doesn't trigger :class TracePoint

[cfis (Charlie Savage) via ruby-core]

Issue #21272 has been updated by cfis (Charlie Savage).


@Eregon - Ah, you are right. Thanks for the pointers to the other issues. Reading them I can see that Class.new is eliminated but I also see this note:

> Before inlining, ObjectSpace would report the allocation class path and method id as Class#new which isn't very helpful. With the inlining patch, we can see that the object is allocated in Foo#test.

It seems like tracepoint doesn't report anything anymore though? Should I move my questions to those tickets? Thanks!

----------------------------------------
Feature #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116320

* Author: st0012 (Stan Lo)
* Status: Open
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




-- 
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[ruby-core:124729] [Ruby Feature#21272] Class.new doesn't trigger :class TracePoint

[cfis (Charlie Savage) via ruby-core]

Issue #21272 has been updated by cfis (Charlie Savage).


Ok, I see, now its `Array#initialize` (or some such). That looks like a nice change, will update ruby-prof.

----------------------------------------
Feature #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116331

* Author: st0012 (Stan Lo)
* Status: Open
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




-- 
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[ruby-core:124730] [Ruby Feature#21272] Class.new doesn't trigger :class TracePoint

[Eregon (Benoit Daloze) via ruby-core]

Issue #21272 has been updated by Eregon (Benoit Daloze).


cfis (Charlie Savage) wrote in #note-6:
> Should I move my questions to those tickets?

Yes, or file a new ticket with a reproduction.

----------------------------------------
Feature #21272: Class.new doesn't trigger :class TracePoint
https://bugs.ruby-lang.org/issues/21272#change-116332

* Author: st0012 (Stan Lo)
* Status: Open
----------------------------------------
According to the official [documentation](https://docs.ruby-lang.org/en/master/TracePoint.html#class-TracePoint-label-Events):

> To filter what is traced, you can pass any of the following as events:
> 
> :class
> Start a class or module definition.

I'd expect `:class` events to be triggered when new classes are defined via `Class.new` as well, but currently that's not the case.

Should we either support `Class.new`, or clarify the behaviour in documentation?

### Reproduction

```rb
TracePoint.trace(:class) do |tp|
  puts "Class created at line: #{tp.lineno}"
end

class Foo; end # Triggers the tracepoint

Baz = Class.new # Doesn't trigger the tracepoint

# ruby test.rb
# Class created at line: 5
```




-- 
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