[ruby-core:92253] [Ruby trunk Feature#15765] [PATCH] Module#name without global constant search

[alanwucanada@gmail.com]

Issue #15765 has been reported by alanwu (Alan Wu).

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Feature #15765: [PATCH] Module#name without global constant search
https://bugs.ruby-lang.org/issues/15765

* Author: alanwu (Alan Wu)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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Hello!

I have put together a reimplementation of `Module#name`, which works by eagerly naming
modules and classes when they are assigned to constants. Besides solving the performance
issues for `Module#name` on anonymous modules, there are some other benefits.

This patch:
 - removes more code than it adds
 - makes normal class and module definition slightly faster (definitions like `class Foo; end`)
 - slightly reduces memory usage for classes and modules due to the removal of a hidden ivar
 - improves the performance of defining modules and classes under an anonymous module. This used to execute a global search.

### Behavior changes and caveats:

```ruby
mod = Module.new
mod::BeforeToS = Module.new
mod.const_set(:BeforeToS2, Module.new)

mod.to_s # on trunk, the VM starts naming modules assigned under mod after calling to_s

mod::AfterToS = Module.new
mod.const_set(:AfterToS2, Module.new)

p mod::BeforeToS.name
p mod::BeforeToS2.name
p mod::AfterToS.name
p mod::AfterToS2.name
```
This prints 4 nils after my patch, as I think the behavior on trunk is unintentional. A few C APIs also have the same effect as calling to_s. They are all changed to be side-effect free.

```ruby
m = Module.new
m::Child = Module.new
Mod = m
p Object.send(:remove_const, :Mod)::Child.name
```
This prints nil on trunk and `Mod::Child` under this patch.

`rb_name_class` is removed, as it does nothing in this new implementation. Not sure if this is public API.

Since the recursive naming is done with a recursive function. When a deeply nested anonymous module is assigned
to a constant, it is technically possible for this implementation to throw a `StackError`. I had a version
which does heap allocation to deal with this, but I picked this version for performance in the common cases.
Anonymous modules are rare as is, and one would have to build a structure nested thousands level deep for this to happen.
On my system it can name a module fifty thousand levels deep without problem.

I think these changes are fairly minimal and acceptable.

---Files--------------------------------
benchmarks.rb (3.16 KB)
0001-Eagerly-name-modules-and-classes.patch (19.8 KB)


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