Allow programmatic override of the default runtime options

[dipinhora]

Prior to this commit, the only way to override the default pony
runtime options was via the command line.

This commit allows for programmatic override of the default pony
runtime options via a specific bare function created on the Main
actor:

fun @runtime_override_defaults(rto: RuntimeOptions) => None

In order to override the values, a programmer would replace the
None with logic to directly set the various options on the rto
variable. This bare function is limited in what is allowed and
is only allowed to call functions on primitives to ensure no
memory allocation occurs as it is called before the runtime is
fully initialized.

This commit also renames the internal variable in options_t from
nopin to pin to better align with how it is set from the
command line so it is easier to programmatically change.

---

Example that sets --ponyhelp to true:

actor Main
  new create(env: Env) =>
    env.out.print("Hello, world.")

  fun @runtime_override_defaults(rto: RuntimeOptions) =>
    rto.ponyhelp = true

[jemc]

This is a clever solution.

Other than my small comment below, it looks good.

One other question, though - what's the best way to document that this feature exists? Should it maybe be mentioned in the pony help output where the runtime options are documented?

[jemc]

Could this be named something less generic than verify_calls? It is very specific to the runtime_override_defaults method, but that isn't clear at all from the name.

[dipinhora]

done

[SeanTAllen]

I feel like this should be documented somewhere. At a minimum, the runtime options Pony class should have documentation for what it does.

I'm open to suggestions on documentation.

[jemc]

Yeah, upon further thought I think for documentation it would be good to:

• add a docstring to the RuntimeOptions type that describes what it does and gives a usage example code snippet
• In the shell usage output where we describe the runtime options and their defaults, we should include a note that the defaults can be modified by the program, and refer the reader to look at the RuntimeOptions type for more details.

[dipinhora]

docstrings and help text added.

This is a clever solution.

clever good or clever bad? i'm not sure......

[SeanTAllen]

@dipinhora this is failing on Windows.

[dipinhora]

@SeanTAllen Yes, it is. It's having troubling finding the new function during link time of libponyc.tests.exe.

Unfortunately, i know almost nothing about windows development or the tools available to debug the issue. Hopefully someone more knowledgeable can help or point me to a guide of some kind that might help me figure things out.

[chalcolith]

I'll take a look tomorrow.

[jemc]

clever good or clever bad? i'm not sure......

😆

Sean uses "clever" as a criticism, but I use it as a compliment!

[chalcolith]

On Windows everything is compiled as C++. Making the function declaration extern "C" should fix the Windows build.

--- a/src/libponyrt/sched/start.c
+++ b/src/libponyrt/sched/start.c
@@ -87,7 +87,13 @@ static opt_arg_t args[] =
  OPT_ARGS_FINISH
};

-void Main_runtime_override_defaults_oo(options_t* opt);
+#ifdef __cplusplus
+extern "C" {
+#endif
+  void Main_runtime_override_defaults_oo(void* opt);
+#ifdef __cplusplus
+}
+#endif

[dipinhora]

@kulibali makes sense. thanks for the help.

[SeanTAllen]

@dipinhora when this gets merged, can you add release notes to #3314?

[SeanTAllen]

Also, can you include an Added section addition for the CHANGELOG?

[SeanTAllen]

When this passes CI, it is good to:

• be squashed with just the original commit message kept
• merged

[SeanTAllen]

Thanks, @dipinhora.

Please add release notes to #3314.