Bug? -- development mode chunk building leads to undefined variables when imports are replaced with vars

[lll000111]

In development mode, some chunks in node_modules/.vite/deps/ are built by putting modules that import one another into the same chunk.

This leads to the import statement of the importing module being removed, because the definition of the imported item now is in the same (chunk) .js file.

Problem: When an import of an exported variable is replaced, the imported module is placed AFTER the importing module in the chunk .js file. But var hoisting still has a sequence to it, assigments are not done in (mathematical) parallel. This leads to undefined when the module importing a constant from another one uses it to calculate another (module top level) constant.

Example:

Source

ModuleA:

export const ALMOST_MoL = 41;

ModuleB:

import {ALMOST_MoL} from 'ModuleA';

const MoL = ALMOST_MoL + 1; 

function logConst() {
    console.log(MoL);
}

Chunk

// ModuleB
var MoL = ALMOST_MoL + 1;   // NaN because Almost_MoL is undefined

function logConst() {
    console.log(MoL);  // NaN
}

// ModuleA
var ALMOST_MoL = 41;

Reproduction requires exported const in one module imported by another module to (on the top level, immediately) produce another const using the imported one.

Then the chunk producing algorithm has to create a chunk that replaces the import by adding the imported module after the importing module in the same .js chunk.

I'll see if I can get an archive that reproduces this, if that is necessary. I'm not sure the chunk producing algorithm always produces such chunks? So I'm not sure how easy it is.

The minimum example to see that one cannot replace ìmport(of constants used immediately) withvar` and rely on hoisting simply is

var T = S + 1;
var S = 41;
console.log(T);  // NaN

Not sure about a bug report. Is this a bug?

I would have to provide a workable example, but I'm not sure the chunk producing algorithm will always create a chunk exactly like this. It could just keep the modules in different chunks, and the imports remain and it all works.