[ruby-core:103108] [Ruby master Feature#17762] A simple way to trace object allocation

Issue #17762 has been updated by Eregon (Benoit Daloze).


`require "objspace/trace"` automatically starting tracing seems dangerous, there is a pretty big performance penalty to enable it.
So I think the message on stderr is needed, and maybe it should be more explicit like `require "objspace/start_tracing"`.

There might be different sorts of tracing so ultimately I feel `ObjectSpace.trace_object_allocations_start` is long but is clear and well-named IMHO.

byroot (Jean Boussier) wrote in #note-2:
> I'm not too sure about that one. I suppose it's fine, but I'm not always in a situation where `p` is usable. Would `Object#allocation_source` be acceptable?

How about `ObjectSpace.allocation_source(obj)`?

`Object#allocation_source` wouldn't work for BasicObject and it would pollute Object/Kernel which seems suboptimal to me.

----------------------------------------
Feature #17762: A simple way to trace object allocation
https://bugs.ruby-lang.org/issues/17762#change-91173

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
----------------------------------------
How about having a short hand to `ObjectSpace.trace_object_allocations_start`, `ObjectSpace.allocation_sourcefile` and `ObjectSpace.allocation_sourceline`?

They are a very powerful tool for debugging and code-reading which allows us to identify an allocation site of an object.
Though they are never lightweight, they are the last resort when you try debugging code written by someone else.

However, the names are too long for me to remember and to type. Whenever I want to use them, I have to google, copy and paste the names.

## Proposal

To enable trace allocations:

```
require "objspace/trace" #=> objspace/trace is enabled
```

To show the allocation site of an object:

```
p obj #=> #<Object:0x...> @ (file.rb):(lineno)
```

## Example

```
require "objspace/trace"
require "active_support/all"

p ActiveSupport::VERSION::STRING
  #=> "6.1.3.1" @ /home/mame/work/ruby/local/lib/ruby/gems/3.1.0/gems/activesupport-6.1.3.1/lib/active_support/gem_version.rb:15
```

## Discussion

I've attached a simple patch that is originally authored by @ko1 .

* Is the message `objspace/trace is enabled` needed or not?
* To stop the trace, you need to use `Object.trace_object_allocations_stop`. But, I guess that it is rare that we need to stop it during debugging.
* Is it too radical to redefine `Kernel#p`? I think that it is good enough for many cases. When it matters, the original APIs (`ObjectSpace.trace_object_allocations_start`, ...) can be used.

---Files--------------------------------
objspace-trace.patch (631 Bytes)


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