[ruby-core:105543] [Ruby master Feature#18231] `RubyVM.keep_script_lines`

["ko1 (Koichi Sasada)" <noreply@ruby-lang.org>]

Issue #18231 has been updated by ko1 (Koichi Sasada).


Some comments:

* For debugger, `Thread::Backtrace::Location#script_lines` is enough.
* If we introduce this feature outside of `RubyVM`, people can use it casually and I'm not sure we can support it well because this feature (keeping all loaded sources). For example, if I install rails with `gem install rails` and `[master]$ du -sh .../lib/ruby/gems/3.1.0/gems/` returns 72MB.

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Feature #18231: `RubyVM.keep_script_lines`
https://bugs.ruby-lang.org/issues/18231#change-94000

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* Target version: 3.1
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This ticket proposes the method `RubyVM.keep_script_lines` to manage the flag to keep the source code.

Now, `SCRIPT_LINES__ = {}` constant is defined, the hash will stores the compiled script with a path name (`{path => src}`). However, `eval` source code doesn't stores in it (maybe because it can be bigger and bigger).

## Proposal

This proposal to add script lines to the ISeq and AST.

```ruby
RubyVM::keep_script_lines = true

eval("def foo = nil\ndef bar = nil")
pp RubyVM::InstructionSequence.of(method(:foo)).script_lines
#=> ["def foo = nil\n", "def bar = nil"]
```

In this case, methods `foo` and `bar` are defined by `eval()` and ISeq of `foo` can returns script lines (all script for `eval`).
`ISeq#script_lines` returns compiled script lines.

When `ISeq` is GCed, then the source code will be also free'ed.

## Discussion

* This feature will be used by debugger (to show the source code) or REPL support (irb and so on) with `error_highlight`.
* Of course memory usage will be increased.
* We can introduce new status `only_eval` in future which will help REPL systems.
* We can implement `ISeq#source` method like `AST#source` method (similar to `toSource` in JavaScript), but this ticket doesn't contain it.

## Implementation

https://github.com/ruby/ruby/pull/4913

For the Ractor support script lines object should be immutable (not implemented yet).




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