Constant folding does not work on polymorphic equality test

[pyrocat101]

Repro

// index.js
let value;
if (process.env.USE === 'foo') {
  value = require('./foo');
} else {
  value = require('./bar');
}
console.log(value);

// foo.js
module.exports = 'foo';

// bar.js
module.exports = 'bar';

Command:

esbuild --bundle index.js '--define:process.env.USE=null' --format=esm

Expected output

foo.js not to be bundled, since null === 'foo' should always evaluate to false.

Actual output

// ...[omitted]
// index.js
var value;
if (null === "foo") {
  value = require_foo();
} else {
  value = require_bar();
}
console.log(value);

However, if the following command is used instead:

esbuild --bundle index.js '--define:process.env.USE="null"' --format=esm

then the constant folding is correctly applied to the if conditions as well as the branch block.

// ...[omitted]
// index.js
var value;
if (false) {
  value = null;
} else {
  value = require_bar();
}
console.log(value);