How do I use my own custom plugin to transform the AST?

[levi-nz]

Apologies in advance if this is documented somewhere, I couldn't find it after searching in docs for over an hour.

I'm trying to run swc compile in.js --config-file build.swcrc --out-file out.js with the following config, using the plugin from the getting started guide. I've verified that the unit test passes, but the code in out.js isn't transformed. How can I make it transform the code as it's supposed to?

{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false,
      "dynamicImport": false,
      "privateMethod": false,
      "functionBind": false,
      "exportDefaultFrom": false,
      "exportNamespaceFrom": false,
      "decorators": false,
      "decoratorsBeforeExport": false,
      "topLevelAwait": false,
      "importMeta": false,
      "preserveAllComments": false
    },
    "target": "es5",
    "loose": false,
    "externalHelpers": false,
    "keepClassNames": false,
    "transform": null,
    "experimental": {
      "plugins": [
        [
          "C:/Users/Levi/CLionProjects/SolarSystems-Software/my-first-plugin/target/wasm32-wasi/debug/my_first_plugin.wasm", {"transform": {}}
        ]
      ]
    }
  },
  "isModule": false
}

Input (produced output is the same):

foo === bar;

Expected output:

kdy1 === bar;

Plugin code:

use swc_core::common::Spanned;
use swc_core::ecma::{
    ast::Program,
    transforms::testing::test,
    visit::{as_folder, FoldWith, VisitMut, VisitMutWith},
};
use swc_core::ecma::ast::{BinExpr, Bool, Ident, op};
use swc_core::plugin::{plugin_transform, proxies::TransformPluginProgramMetadata};

pub struct TransformVisitor;

impl VisitMut for TransformVisitor {
    // Implement necessary visit_mut_* methods for actual custom transform.
    // A comprehensive list of possible visitor methods can be found here:
    // https://rustdoc.swc.rs/swc_ecma_visit/trait.VisitMut.html
    fn visit_mut_bin_expr(&mut self, e: &mut BinExpr) {
        e.visit_mut_children_with(self);

        if e.op == op!("===") {
            e.left = Box::new(Ident::new("kdy1".into(), e.left.span()).into());
        }
    }
}

/// An example plugin function with macro support.
/// `plugin_transform` macro interop pointers into deserialized structs, as well
/// as returning ptr back to host.
///
/// It is possible to opt out from macro by writing transform fn manually
/// if plugin need to handle low-level ptr directly via
/// `__transform_plugin_process_impl(
///     ast_ptr: *const u8, ast_ptr_len: i32,
///     unresolved_mark: u32, should_enable_comments_proxy: i32) ->
///     i32 /*  0 for success, fail otherwise.
///             Note this is only for internal pointer interop result,
///             not actual transform result */`
///
/// This requires manual handling of serialization / deserialization from ptrs.
/// Refer swc_plugin_macro to see how does it work internally.
#[plugin_transform]
pub fn process_transform(program: Program, _metadata: TransformPluginProgramMetadata) -> Program {
    program.fold_with(&mut as_folder(TransformVisitor))
}

// An example to test plugin transform.
// Recommended strategy to test plugin's transform is verify
// the Visitor's behavior, instead of trying to run `process_transform` with mocks
// unless explicitly required to do so.
test!(
    Default::default(),
    |_| as_folder(TransformVisitor),
    boo,
    // Input codes
    r#"foo === bar;"#,
    // Output codes after transformed with plugin
    r#"kdy1 === bar;"#
);

[kwonoj]

I don't see a problem with codes / config above. What platform are you on?

[levi-nz]

I'm using macOS on M2. I was trying on Windows (x86, AMD processor) initially, same result on there too.

[kwonoj]

There's no reason I can see plugin doesn't run on those platform. Without having repro, hard to guess even. Can you setup CI to repro this?

[levi-nz]

@kwonoj I'll setup CI if you want -- should I just make my own repo with GitHub Actions or something?

I think this is an SWC bug or something because even other plugins don't work with this same command that I put in my original post.

[kwonoj]

yes, setup ci or codesandbox or anything. I just tried locally and confirmed at least plugin is loading correctly with published version of swc. I do not believe this is a swc bug.

[kwonoj]

Just note, there's no swc compile command - legacy @swc/cli does not have swc command, and if you're using latest it should be swcx compile instead.