SSR: References to named default export functions get out of scope

[GrygrFlzr]

Describe the bug

When any code meets all of the following criteria:

• Is loaded using ssrLoadModule
• Has a default named export
• Has a reference to the above name in the same file

ssrLoadModule will incorrectly treat it as an anonymous function, preventing the rest of the code from accessing it.

This code style is used in various dependencies such as d3-format in order to modify function prototypes.

For example:

export default function hello() {
  return 1234;
}

console.log(typeof hello);
// returns undefined

hello.test = 1234;
// [vite] Error when evaluating SSR module
// ReferenceError: hello is not defined

As a sanity check, I have confirmed that:

• The above code executes as expected when directly run from node
• The default export is properly named when splitting the export from the function definition:

  function hello() { /* ... */ }
  export default hello;
  console.log(typeof hello);
  // returns function

• Named exports are not affected

  export function hello() { /* ... */ }
  console.log(typeof hello);
  // returns function

This is because of the ssrTransform step doesn't look for references to the default export, it only replaces export default with __vite_ssr_exports__.default =:

vite/packages/vite/src/node/ssr/ssrTransform.ts

Lines 125 to 132 in e092e89

	// default export
	if (node.type === 'ExportDefaultDeclaration') {
	s.overwrite(
	node.start,
	node.start + 14,
	`${ssrModuleExportsKey}.default =`
	)
	}

Producing the following transformed code:

__vite_ssr_exports__.default = function hello() {
        return 1234;
}

console.log(typeof hello);
hello.test=1234;

Which now makes hello out of scope.

Reproduction

https://github.com/GrygrFlzr/vite-ssr-default

You can see the logs from CI runs:

• Windows + Node 14.17.1
• macOS + Node 14.17.1
• Ubuntu + Node 14.17.1
• Ubuntu + Node 16.4.0

System Info

System:
    OS: Windows 10 10.0.22000
    CPU: (16) x64 AMD Ryzen 7 3700X 8-Core Processor
    Memory: 14.00 GB / 31.93 GB
  Binaries:
    Node: 14.16.0 - C:\program files\nodejs\node.EXE
    Yarn: 1.22.10 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 6.14.13 - C:\program files\nodejs\npm.CMD
  Browsers:
    Chrome: 91.0.4472.124
    Edge: Spartan (44.22000.1.0), Chromium (91.0.864.59)
    Internet Explorer: 11.0.22000.1
  npmPackages:
    vite: ^2.4.0-beta.2 => 2.4.0-beta.2

Used Package Manager

pnpm

Logs

> vite-ssr-default@1.0.0 dev /home/runner/work/vite-ssr-default/vite-ssr-default
> node server

The variable "app" is of type undefined
9:46:16 AM [vite] Error when evaluating SSR module /src/app.js:
ReferenceError: app is not defined
    at /src/app.js:6:1
    at instantiateModule (/home/runner/work/vite-ssr-default/vite-ssr-default/node_modules/.pnpm/vite@2.4.0-beta.2/node_modules/vite/dist/node/chunks/dep-06e8fbb4.js:72663:166)
ReferenceError: app is not defined
    at /src/app.js:6:1
    at instantiateModule (/home/runner/work/vite-ssr-default/vite-ssr-default/node_modules/.pnpm/vite@2.4.0-beta.2/node_modules/vite/dist/node/chunks/dep-06e8fbb4.js:72663:166)

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/vue-next instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.