[REPL] Cannot declare variables under strict-mode when used along --experimental-top-level-await

[ejose19]

• Version: v16.4.1
• Platform: Archlinux
• Subsystem: N/A

What steps will reproduce the bug?

• run node with: node --use_strict --experimental-repl-await
• enter: const x = await 1;
• receive:

Uncaught ReferenceError: x is not defined
    at REPL1:1:24
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

How often does it reproduce? Is there a required condition?

100%

What is the expected behavior?

It shouldn't throw error, or if this is not supported then it should error out before starting repl.

What do you see instead?

Error is thrown

Additional information

This is related to handling in

node/lib/internal/repl/await.js

Lines 53 to 74 in c2e6822

	VariableDeclaration(node, state, c) {
	if (node.kind === 'var' ||
	state.ancestors[state.ancestors.length - 2] === state.body) {
	if (node.declarations.length === 1) {
	state.replace(node.start, node.start + node.kind.length, 'void');
	} else {
	state.replace(node.start, node.start + node.kind.length, 'void (');
	}
	ArrayPrototypeForEach(node.declarations, (decl) => {
	state.prepend(decl, '(');
	state.append(decl, decl.init ? ')' : '=undefined)');
	});
	if (node.declarations.length !== 1) {
	state.append(node.declarations[node.declarations.length - 1], ')');
	}
	}
	walk.base.VariableDeclaration(node, state, c);
	}
	};

as it's replacing const with void ($exp) without any flag to omit if running in strict mode.

This was noticed when trying to implement TLA in repl for ts-node.

[guybedford]

We should be declaring let and const vars as top-level scope vars not globals. This can be accomplished by hoisting the variable definition outside of the async wrapper, separate from its assignment. In the process we should probably convert const into let, as that is likely the best we can do as well.

@ejose19 is this something you might be able to contribute to here? It is also a blocker for #39142.

[guybedford]

The tests for this are in https://github.com/nodejs/node/blob/master/test/parallel/test-repl-preprocess-top-level-await.js#L62.

The suggested change is the following to the last test case:

  ['let o = await 1, p',
    '(async () => { void ( (o = await 1), (p=undefined)) })()' ],

->

  ['let o = await 1, p',
    'let o, p; (async () => { void ( (o = await 1), (p=undefined)) })()' ],

[ejose19]

@guybedford Sure, this is also needed for ts-node so I'll try to get it fixed.

[ejose19]

@guybedford I've submitted a PR, let me know what you think.

[guybedford]

Fixed in #39265.