[ItsRenjiii]

Rollup Plugin Name: commonjs

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Reported in discussion #2043 (no issue filed).

Description

A module whose only export is a top-level module.exports = ... assignment uses exportMode === 'replace'. When it also gets a require wrapper, its exports variable is declared with no value:

var a;
var hasRequiredA;

function requireA () {
	if (hasRequiredA) return a;
	hasRequiredA = 1;
	const b = requireB();
	a = { seenByB: b.seen };
	return a;
}

A circular require that reaches the module before the assignment runs therefore gets undefined, where Node gives it the initial {} exports object. A top-level this used before the assignment is also undefined, so this.x = 1 throws TypeError: Cannot set properties of undefined.

This PR gives the variable Node's initial {} in both places it can be read early:

• With a require wrapper, a = {}; is set when the first require starts, right after the hasRequiredA guard. Setting it there rather than at module level keeps a value that a re-entrant require already completed: in a mixed ES/CommonJS cycle a module-level var a = {}; can run after requireA() has finished and erase its exports.
• Without a require wrapper (strictRequires: false, or 'auto'/'debug' for a module outside a cycle), top-level this is rewritten to a and runs before var a = .... When the module uses top-level this, it now gets var a = {}; before the body, and the assignment becomes a plain a = .... Other unwrapped modules produce the same output as before.

The module.exports = assignment still replaces the object once it runs.

Reproduction from the discussion (rollup 4.68.0, @rollup/plugin-commonjs 29.0.3):

	node entry.js	bundle before	bundle after
circular require (strictRequires: true / 'auto')	{ seenByB: 'object' }	{ seenByB: 'undefined' }	{ seenByB: 'object' }
this.x = 1 before module.exports = (true / 'auto' / false)	{ y: 2 }	TypeError	{ y: 2 }

A cycle with strictRequires: false still gives undefined, as on master, because that mode does not support cycles.

Tests

• New function fixtures:
  • strict-requires-circular-replace (cycle) and strict-requires-this-before-replace, this-before-replace-auto and this-before-replace-unwrapped (top-level this under true, 'auto' and false). All four fail on master.
  • strict-requires-circular-replace-mixed: the mixed ES/CommonJS cycle from review. It fails on this PR's first commit and passes now.
• The updated form outputs and snapshots change only var x; + x = {}; inside the require function, plus one chunk hash that follows from its content.
• The steps from validate.yml all pass locally: pnpm install --frozen-lockfile, prettier:check, pnpm --recursive build, lint:js and ci:coverage for ...[origin/master]. The commonjs suite (296 tests) passes on Node 20 and 24.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; both previous failures are addressed.

_{Reviews (2) · Last reviewed commit: "fix(commonjs): set replaced exports on f..." · Reviewed by Greptile}