feat: specify initial value for exec_scopes

[odesenfans]

Context: bootloader and Starknet OS support.

Added a cairo_run_program_with_initial_scope function that allows to run a program with a customized execution scope. cairo_run_program now calls this function with an empty execution scope.

We need a way to set initial variables inside the execution scopes to pass bootloader/OS arguments. The Python VM relies on a program input file and uses hints to deserialize this input. In most cases we do not want to have to deserialize these input types, but rather pass them directly as variables inside the root execution scope.

Possible alternatives:

1. Pass init values inside CairoRunConfig.
2. Support a more generic string argument for program input, at the expense of having to make all input structures deserializable. This has proven to be complex because some bootloader structures rely on Program and CairoPie, so I'd prefer not to go down that road.

Checklist

• Linked to Github Issue
• Unit tests added
• Integration tests added.
• This change requires new documentation.
  • Documentation has been added/updated.
  • CHANGELOG has been updated.

[fmoletta]

This seems like a very specific behaviour, I would rather have it added to the CairoRunConfig struct, so users can just ignore it (aka leave it to the Default impl to handle).

[odesenfans]

This seems like a very specific behaviour, I would rather have it added to the CairoRunConfig struct, so users can just ignore it (aka leave it to the Default impl to handle).

One issue with that is that we get a &CairoRunConfig as argument so we can't move the exec_scopes field out, and ExecutionScopes is not Clone because of the Box<dyn Any> values inside it. A solution could be to pass an owned CairoRunConfig directly to cairo_run. There is no particular reason to keep that structure around after the run. CairoRunConfig is not Clone so this is not an issue, but it could be slightly annoying for existing code that reads values from CairoRunConfig after the call to cairo_run.

What do you think @fmoletta ?

[Oppen]

It's not clear to me that you can't do this via a regular hint that you run as part of your program load process. Is there something getting in the way of doing that?

[odesenfans]

It's not clear to me that you can't do this via a regular hint that you run as part of your program load process. Is there something getting in the way of doing that?

@Oppen yes. You need to load these initial variables from somewhere. You could say "let's load it from the file system" but a) that involves some useless serialization/deserialization which is not that easy with types like Program and CairoPie, b) without other inputs the hint needs to use a hardcoded path, which is not ideal and c) I feel like the ability to build your inputs programmatically and pass them as needed is not that unreasonable a request for the OS and bootloader.

Anecdotally, this feature exists for the Python VM (see here).

[fmoletta]

This seems like a very specific behaviour, I would rather have it added to the CairoRunConfig struct, so users can just ignore it (aka leave it to the Default impl to handle).

One issue with that is that we get a &CairoRunConfig as argument so we can't move the exec_scopes field out, and ExecutionScopes is not Clone because of the Box<dyn Any> values inside it. A solution could be to pass an owned CairoRunConfig directly to cairo_run. There is no particular reason to keep that structure around after the run. CairoRunConfig is not Clone so this is not an issue, but it could be slightly annoying for existing code that reads values from CairoRunConfig after the call to cairo_run.

What do you think @fmoletta ?

Oh, then we could go with the current solution and rename cairo_run_program to cairo_run_program_with_initial_scope and add a cairo_run_program that calls it so we can keep the cairo_run_program signature as it is now

[odesenfans]

Oh, then we could go with the current solution and rename cairo_run_program to cairo_run_program_with_initial_scope and add a cairo_run_program that calls it so we can keep the cairo_run_program signature as it is now

Done: 45e929e