deno/cli/napi/sym/README.md

napi_sym

A proc_macro for Deno's Node-API implementation. It does the following things:

• Marks the symbol as #[no_mangle] and rewrites it as pub extern "C" $name.
• Asserts that the function symbol is present in symbol_exports.json.
• Maps deno_napi::Result to raw napi_result.

use deno_napi::napi_value;
use deno_napi::Env;
use deno_napi::Error;
use deno_napi::Result;

#[napi_sym::napi_sym]
fn napi_get_boolean(
  env: *mut Env,
  value: bool,
  result: *mut napi_value,
) -> Result {
  let _env: &mut Env = env.as_mut().ok_or(Error::InvalidArg)?;
  // *result = ...
  Ok(())
}

symbol_exports.json

A file containing the symbols that need to be put into the executable's dynamic symbol table at link-time.

This is done using /DEF: on Windows, -exported_symbol,_ on macOS and --export-dynamic-symbol= on Linux. See cli/build.rs.

On Windows, you need to generate the .def file by running tools/napi/generate_symbols_lists.js.