Instrumentation can block creation of vars in outside scope with sloppy-mode direct eval()

[overlookmotel]

Problem

Input:

// CommonJS - sloppy mode
eval('var x = 123; let livepack_tracker;');
assert(typeof x === 'number');

In original code, assertion passes. In instrumented code, it fails.

Due to usage of a var livepack_tracker in the eval()-ed code, Livepack's instrumentation wraps the eval code in an arrow function to populate internal livepack_tracker1 var. The code which is executed in eval() is:

(
  (livepack1_tracker, livepack1_getScopeId) =>
  eval('var x = 123; let livepack_tracker;')
)(livepack_tracker, livepack_getScopeId)

This means var x is added to the scope of the arrow function, not the outer scope.

Only a occurs if:

1. eval() code is sloppy mode. In strict mode var declarations are bound within the eval script scope.
2. eval()-ed code uses vars which could clash with Livepack's internal vars in outer scope (very uncommon case)

Solution

Can avoid the arrow function wrapper, by instead transforming eval()-ed code to:

const livepack1_tracker = livepack_tracker,
  livepack1_getScopeId = livepack_getScopeId;
eval('var x = 123; let livepack_tracker;');

NB Indirect eval also has similar problems, but solution is more complex. Will open separate issue for that.

[overlookmotel]

Actually, this problem occurs even if no internal vars are used.

Input:

// CommonJS - sloppy mode
eval('var x = 123;');
assert(typeof x === 'number');

This is instrumented as:

livepack_tracker.evalDirect(
  'var x = 123',
  eval,
  livepack_temp_3 => eval(livepack_temp_3),
  livepack_temp_3 => eval(...livepack_temp_3),
  [[1, "index", livepack_scopeId_2, ["module"], ["exports"], ["this", 1], ["new.target", 1]]],
  false
);

So eval() is still called within an arrow function.

To solve it, would need to convert to something like:

eval( livepack_tracker.instrumentEval( 'var x = 123', eval, [ /* ... */ ] ) )

Previously took this approach (function was called livepack_preval) but later changed it, but can't remember why.

[overlookmotel]

See #137 (comment) for a solution.