Inlining function call w/ object assignment causes variable to be accessed before assignment

[arshaw]

Describe the bug

Something is going wrong with function inlining and object property assignment. Please see my expected/actual and input/output below:

Input code

console.log(doSomething())

function doSomething() {
  return fabricateEvent()
}

function fabricateEvent() {
  let def = createEventDef()

  return {
    def,
    ui: compileEventUi(def),
  }
}

function compileEventUi(def) {
  let uis = []
  uis.push(def.ui)
  return uis
}

function createEventDef() {
  return {
    id: 'fakeId',
    ui: 'something'
  }
}

Config

{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false
    },
    "target": "es2018",
    "loose": false,
    "minify": {
      "compress": {
        "arguments": false,
        "arrows": true,
        "booleans": true,
        "booleans_as_integers": false,
        "collapse_vars": true,
        "comparisons": true,
        "computed_props": true,
        "conditionals": true,
        "dead_code": true,
        "directives": true,
        "drop_console": false,
        "drop_debugger": true,
        "evaluate": true,
        "expression": false,
        "hoist_funs": false,
        "hoist_props": true,
        "hoist_vars": false,
        "if_return": true,
        "join_vars": true,
        "keep_classnames": false,
        "keep_fargs": true,
        "keep_fnames": false,
        "keep_infinity": false,
        "loops": true,
        "negate_iife": true,
        "properties": true,
        "reduce_funcs": false,
        "reduce_vars": false,
        "side_effects": true,
        "switches": true,
        "typeofs": true,
        "unsafe": false,
        "unsafe_arrows": false,
        "unsafe_comps": false,
        "unsafe_Function": false,
        "unsafe_math": false,
        "unsafe_symbols": false,
        "unsafe_methods": false,
        "unsafe_proto": false,
        "unsafe_regexp": false,
        "unsafe_undefined": false,
        "unused": true,
        "const_to_let": true,
        "pristine_globals": true,
        "passes": 2
      },
      "mangle": false
    }
  },
  "module": {
    "type": "es6"
  },
  "minify": false,
  "isModule": true
}

Playground link

https://play.swc.rs/?version=1.3.32&code=H4sIAAAAAAAAA22Quw6CMBSG9z7F2aCJ4QFI3HRwNk7GAcspnFha04uL4d1tQeQStybffzsVRjujsFCmyWtzNh36lnSTc86YDFp4MhpWAN4MwKIPVoOs7pZE5fH4Qu1zzvqFawsHo0IPNUrYg7A4sQPK6J1jkxCSbDc8ApUgTPckNcovlEfGE%2BxXjX9Ev9JALpZebyzlueIZXJsERSA%2BF0eyDtxsXN4%2BjqS6hExWDzzV2bw2c9N%2FZd%2BRH343a9FoAQAA&config=H4sIAAAAAAAAA22TQZLjIAxF7%2BJ1FjO9mJrqA8yuz0ApIBy6MXIhkY4rlbu3cGwcJ7Oznr%2BE%2BBLX7pNt937tRsiMuX7xlAQu3XuHdgC2OYzSHVSmyENkvB06gdyjVAm%2F%2Ffr9V39HIsZFcOiGkIKfajFLw5iRuX5rUhkwCTcd5EzfGkouGh2JIkJ6iQ2wCUmwx7ylWooRRkZzhtwy6mmQA1PaoSLozJhpfKDJBQmUtNjKHIIzlhw2EDJaCWfcJFpDJYm1sdbJDB0eS99XA%2B9KPEMsIK0WXmYb9MSWd6LAYnxJ%2FIR2nd7R%2FZKLKniTUUpOq%2BaTQtr58IWofUZgTjDgljlzr3PYK%2F1%2FVCF5HaJMjeqEt64S9no5E4JvN6xdY5awuZXRFYv1hnYrvsDdhTg4NOi9ut2S%2BTuIPW3FZBqRfAvVNfDbDO6hWfdpT%2BsKvMB%2F2pU8jmPhA8jpmfE0HCm%2BlBhQTuResBoh9Ayzbu9lfKYlOVSb0T38KFzDtqY6fCET62tbfdaF0BzTRzo%2BrO%2Bo0652ven7HCD1bUNvFZArFVxnH%2BeH%2B6e7bQ913Sz%2BWIS15u0HsrmeNh0EAAA%3D

Expected behavior

When running, something like {def: {…}, ui: Array(1)} should be outputted. The def property should be populated.

Actual behavior

When running, the output is {def: undefined, ui: Array(1)}. The def property is undefined.

The cause of the bug is obvious when looking at the compiled code. The def1 variable is assigned to an object property before it is populated.

console.log(function() {
    var def;
    let def1, uis;
    return {
        def: def1,
        ui: (def = def1 = {
            id: 'fakeId',
            ui: 'something'
        }, (uis = []).push(def.ui), uis)
    };
}());

There is some sort of bug with inlining functions and object literal property assignment.

Version

1.3.32

Additional context

This bug is affecting:

• next.js: SWC breaks full calendar vercel/next.js#44983
• fullcalendar: Full calendar not selectable with Next.js fullcalendar/fullcalendar#7155

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.