[Plugin development] Different scopes of variables in tests and in the transform

[mytecor]

Hey, I'm writing a small plugin to wrap code into a block statement:

Plugin source

use swc_core::ecma::ast::{BlockStmt, Module, ModuleItem, Stmt};
use swc_core::ecma::{ast::Program, transforms::testing::test_inline};
use swc_core::plugin::{plugin_transform, proxies::TransformPluginProgramMetadata};
use swc_core::quote;
use swc_ecma_visit::{as_folder, noop_visit_mut_type, VisitMut, VisitMutWith};

struct Transformer {}

impl VisitMut for Transformer {
    noop_visit_mut_type!();

    fn visit_mut_module(&mut self, node: &mut Module) {
        let block_body = node
            .body
            .clone()
            .into_iter()
            .filter_map(|module_item| {
                return match module_item {
                    ModuleItem::Stmt(stmt) => Some(stmt),
                    _ => None,
                };
            })
            .collect();

        node.body = vec![
            quote!("const test = {}" as ModuleItem),
            BlockStmt {
                stmts: block_body,
                ..Default::default()
            }
            .into(),
        ];
    }
}

#[plugin_transform]
pub fn process_transform(
    mut program: Program,
    _metadata: TransformPluginProgramMetadata,
) -> Program {
    let mut plugin = Transformer {};
    program.visit_mut_with(&mut plugin);
    return program;
}

test_inline!(
    Default::default(),
    |_| as_folder(Transformer {}),
    test,
    // Input
    r#"test.foo = 123"#,
    // Expected
    r#"
    const test = {}

    {
        test.foo = 123
    }
    "#
);

Then js code:

const source = 'test.foo = 123'
const output = await transform(source, {
  jsc: {
    target: 'esnext',
    experimental: {
      plugins: [[fileURLToPath(import.meta.resolve('transformer')), {}]],
    },
  },
})

Will produce:

const test1 = {};
{
    test.foo = 123;
}

Questions:

1. I don't quite understand what ctxt I should set, there is not enough information on this topic in the documentation for me. Should I need to check all identifiers within a block statement?
2. As I understand, hygiene is not used during tests. What is the correct way to test such plugins?
3. Btw how can I print the ast for debug? (newbie in rust)

[kdy1]

For 2, it's recommended to apply a resolver before your plugin while testing. https://swc.rs/docs/plugin/ecmascript/cheatsheet#apply-resolver-while-testing

[leafypout]

For ctxt, you can either apply default SyntaxContext (Default::default()) and then apply resolver pass again, or create a new context with SyntaxContext::empty().apply_mark(Mark::new()). The latter is faster because you don't have to apply resolver twice and I believe it does the same thing.

[mytecor]

Thanks, I preferred the second option.