How to log in an SWC plugin ?

[edmondop]

I am building an SWC plugin compatible with NextJS 14.2.2 using tracing as recommended in the docs and adopting the version of SWC crates compatible for NextJS 14.2.2.

swc_common = { version = "0.33.19", features = ["concurrent"] }
swc_core = { version = "0.90.22", features = ["ecma_plugin_transform"] }
swc_ecma_ast = "0.112.5"
swc_ecma_utils = "0.127.12"
swc_ecma_visit = "0.98.6"
swc_plugin_macro = "0.9.16"
tracing          = { version = "0.1.40", features = ["release_max_level_off"] }

My SWC plugin is correctly started (if I panic/exit I could see the error log in the NextJS console) however all calls to tracing::info! macro are swallowed. I tried both to launch RUST_LOG=debug next dev and to specify the env variable in my next.config.js like so:

/** @type {import('next').NextConfig} */
const path = require("node:path");
// const isographSwcPlugin = "@isograph/swc-plugin";
const isographSwcPlugin = path.join(
  __dirname,
  "../../crates/swc_plugin/swc_plugin_isograph.wasm",
);

module.exports = {
  experimental: {
    swcPlugins: [[isographSwcPlugin, {}]],
  },
  env: {
    RUST_LOG: "info", // Set desired log level
  },
};

Should I add a dependency to tracing-subscriber? I checked the existing plugins and none of them has this explicit dependency/sets up the subscriber