Top-level await leads to complexity explosion with cyclic imports

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:

[andersk]

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

[webpack-bot]

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