swc-plugin-formatjs

Rust/SWC port of babel-plugin-formatjs. Version lock-stepped with the upstream npm package — swc-plugin-formatjs 10.5.41 mirrors babel-plugin-formatjs@10.5.41.

Ships in two consumption modes from a single crate:

• WASI plugin for @swc/core's wasm plugin host.
• Native rlib that links into a native @swc/core build via swc::Compiler::process_js_with_custom_pass.

Native usage

use swc::{config::{Config, IsModule, Options}, Compiler};
use swc_core::common::{errors::Handler, FileName, SourceMap, GLOBALS};
use swc_core::ecma::ast::noop_pass;
use swc_plugin_formatjs::{formatjs_pass, Config as FormatJsConfig};
use std::sync::Arc;

GLOBALS.set(&Default::default(), || {
    let cm: Arc<SourceMap> = Default::default();
    let handler = Handler::with_emitter_writer(Box::new(std::io::stderr()), Some(cm.clone()));
    let compiler = Compiler::new(cm.clone());

    let fm = cm.new_source_file(
        Arc::new(FileName::Real("input.tsx".into())),
        source.to_string(),
    );

    let opts = Options {
        config: Config {
            is_module: Some(IsModule::Bool(true)),
            ..Default::default()
        },
        swcrc: false,
        ..Default::default()
    };

    let result = compiler.process_js_with_custom_pass(
        fm, None, &handler, &opts,
        swc_core::common::comments::SingleThreadedComments::default(),
        |_| formatjs_pass(FormatJsConfig::default()),
        |_| noop_pass(),
    ).unwrap();
});

WASI plugin usage

Configure via @swc/core's experimental.plugins:

require("@swc/core").transform(source, {
  jsc: {
    parser: { syntax: "typescript", tsx: true },
    experimental: {
      plugins: [
        ["swc-plugin-formatjs", {
          idInterpolationPattern: "[sha512:contenthash:base64:6]",
          removeDefaultMessage: false,
        }],
      ],
    },
  },
});

Version-compat matrix

These are deliberately exact-pinned. Drifting any of them is a behavior change — re-run the upstream parity harness before publishing.

Supported options

Mirrors the babel Options interface that real upstream consumers exercise:

• idInterpolationPattern (default: [sha512:contenthash:base64:6])
• removeDefaultMessage
• additionalComponentNames
• additionalFunctionNames
• preserveWhitespace

Hard-error policy

Where babel's plugin would silently fold a non-literal defaultMessage via path.evaluate() (string concatenation, identifier-to-const refs), this port hard-errors through swc_common::errors::HANDLER and halts the transform. The motivation is: silent misses across a large codebase are far more expensive than a loud build break that points to a single line.

Specifically rejected (with span-attached diagnostics):

• Non-string-literal id / defaultMessage / description (call expression and JSX)
• Spread (...rest) inside a message descriptor object
• Computed or numeric property keys in a descriptor
• Shorthand { defaultMessage } for descriptor fields
• Empty defaultMessage="" with no id
• Computed-member callees (intl[fnName](...))
• ast: true, extractSourceLocation, pragma, overrideIdFn, onMsgExtracted, onMetaExtracted config options
• idInterpolationPattern tokens other than [hash...]/[contenthash...]
• Hash type ≠ sha512 and digest type ≠ base64/hex

JSX spread without an explicit defaultMessage attr (<FormattedMessage {...descriptor} />) is silently skipped, matching babel exactly — the descriptor is assumed to be extracted at the spread source.

License

MIT