Top-level await leads to complexity explosion with cyclic imports

[andersk]

Bug report

What is the current behavior?

In a project with cyclic imports, top-level await leads to a massive complexity explosion. On a complete graph of n nodes, the time and memory grows as Θ(n!), which gets very bad quickly.

If the current behavior is a bug, please provide the steps to reproduce.

1. Create the following file as 0.js:

   export const c = await null;

2. Create the following file as 1.js, and copy it to 2.js, 3.js, 4.js, 5.js, 6.js, 7.js, 8.js, 9.js and src.js:

   import "./0.js";
   import "./1.js";
   import "./2.js";
   import "./3.js";
   import "./4.js";
   import "./5.js";
   import "./6.js";
   import "./7.js";
   import "./8.js";
   import "./9.js";

   (Note that none of the import cycles pass through 0.js, so this should be fine.)

3. Run webpack --mode=development --experiments-top-level-await. (No additional configuration file is needed.)

4. Run 'time' node dist/main.js.

   $ 'time' node dist/main.js 
   7.57user 0.42system 0:07.53elapsed 106%CPU (0avgtext+0avgdata 1271408maxresident)k
   0inputs+0outputs (0major+333169minor)pagefaults 0swaps

As you can see, this takes over 7 seconds and 1.2 gigabytes of memory.

If you insert a console.log statement into the whenAll function in dist/main.js, you’ll see that it gets called exactly ⌊10! ⋅ e⌋ − 1 = 9864100 times.

What is the expected behavior?

This should run almost immediately with very little memory.

Other relevant information:
webpack version: 5.72.0
Node.js version: 16.15.0
Operating System: NixOS 22.05
Additional tools:

[vankop]

for me all works as expected

please create a reproducible repo

[andersk]

@vankop Your screenshot shows that you’ve copied the 29-byte file ten times. The recipe I gave above has one 29-byte file, and ten copies of the 170-byte file. Like this:

https://gist.github.com/andersk/0af1a0654516fb53ba7b8e757be4db85

[andersk]

In fact, cyclic imports are not necessary to reproduce this. Here’s an example with 24 modules taking 12 seconds and 1.9 gigabytes, with 2²³ − 1 = 8388607 calls to whenAll.

https://gist.github.com/andersk/034cf3103f15f16f7088aae525f15496

$ webpack --mode=development --experiments-top-level-await
$ 'time' node dist/main.js
12.52user 0.72system 0:10.97elapsed 120%CPU (0avgtext+0avgdata 1890260maxresident)k
0inputs+0outputs (0major+536615minor)pagefaults 0swaps

[webpack-bot]

This issue had no activity for at least three months.

It's subject to automatic issue closing if there is no activity in the next 15 days.

[andersk]

This seems to have been fixed in v5.73.0 by #15899.