[ruby-core:115501] [Ruby master Feature#20005] Add C API to return symbols of native extensions resolved from features

Issue #20005 has been updated by tagomoris (Satoshi Tagomori).


nobu (Nobuyoshi Nakada) wrote in #note-9:
> `dln_sym` has been used only to resolve and call immediately `Init_xxx` functions, and it would be reasonable to split error handling.

That makes sense.

> > My expectation: libraries should raise LoadError under their own responsibility when this API returns NULL
> 
> What do you mean by "libraries" here?

I meant extensions, that call this API.

The diff you pasted is really helpful. Just one point I have a question:

```diff
+#define dln_sym_call(rettype, argtype, handle, symbol) \
+    (*(rettype (*)argtype)dln_sym_func(handle, symbol))
```

This actually does not call the symbol but returns a callable symbol. So I think it's better to either:
A. rename it to `dln_sym_callable`
B. add `()` at the end of the line, and remove `()` from the code about `"ruby_abi_version"` and `init_fct_name`.

@nobu What do you think?

----------------------------------------
Feature #20005: Add C API to return symbols of native extensions resolved from features
https://bugs.ruby-lang.org/issues/20005#change-105430

* Author: tagomoris (Satoshi Tagomori)
* Status: Open
* Priority: Normal
----------------------------------------
I want an API to resolve symbols of other native extensions by a feature name and a symbol name (just like `dlsym`).

(`rb_dln_resolve_symbol` is an example function name of this feature in the example below)
```c
// "a_client_open" is a function defined in "/..../a_client.so", that should be loaded in Ruby beforehand.

// in the extension to be "a.so"
VALUE (*a_client_open)(VALUE);

void Init_a(void)
{
  a_client_open = (VALUE(*)(VALUE))rb_dln_resolve_symbol("a_client", "a_client_open");
  // the return value may be NULL if the symbols is not found
}
```

This API is to replace direct reference of external symbols.

Currently, native extensions have to just call the function of other extensions directly on the assumption of:
* The dependency native extension is already loaded
* The symbol is defined correctly in the dependency (the version of dependency is correct&expected)
Otherwise, it crashes.

This API provides a way for developers to raise exceptions if the resolved symbol is `NULL`, and these exceptions can display meaningful messages and instructions to the users of extensions.




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