`NestJS` application initialised twice with `SWC`

[lintellme99]

Describe the bug

Application initializes twice when using SWC with NestJS nest start --watch (npm run start:dev in the repo's scripts), even though with nest start (npm run start in the repos' scripts) it works fine, without unnecessary re-initialize

I've upload the whole code to the repository (with README.md) where you can reproduce this bug: https://github.com/lintellme99/nestjs-swc-bug

Input code

No response

Config

{
  "$schema": "https://json.schemastore.org/swcrc",
  "jsc": {
    "parser": {
      "syntax": "typescript",
      "decorators": true,
      "dynamicImport": true
    },
    "transform": {
      "legacyDecorator": true,
      "decoratorMetadata": true
    },
    "baseUrl": "./src"
  }
}

Playground link (or link to the minimal reproduction)

https://github.com/lintellme99/nestjs-swc-bug

SWC Info output

Operating System: Platform: darwin Arch: arm64 Machine Type: arm64 Version: Darwin Kernel Version 23.1.0: Mon Oct 9 21:32:11 PDT 2023; root:xnu-10002.41.9~7/RELEASE_ARM64_T6030 CPU: (12 cores) Models: Apple M3 Pro

Binaries:
    Node: 20.7.0
    npm: 10.1.0
    Yarn: N/A
    pnpm: N/A

Relevant Packages:
    @swc/core: 1.7.6
    @swc/helpers: N/A
    @swc/types: 0.1.12
    typescript: 5.5.4

SWC Config:
    output: N/A
    .swcrc path: N/A

Next.js info:
    output: N/A

Expected behavior

NestJS nest start --watch command executes only one initializition of main.ts file and bootstrap function

Actual behavior

NestJS nest start --watch command executes two initializitions of main.ts file and bootstrap function

Version

"@swc/cli": "0.4.0", "@swc/core": "1.7.6"

Additional context

No response

[lintellme99]

An interesting fact is that if you add a few more files that swc will have to process (I just cloned all files 6 times with different names), then the bug will disappear

As soon as I had 38 files Successfully compiled: 38 files with swc (37.96ms) instead of the 6 with which the bug is playing, it stopped reproducing:

TSC Initializing type checker...[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [NestFactory] Starting Nest application...
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] KyselyModule dependencies initialized +6ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] ConfigHostModule dependencies initialized +0ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] AppModule dependencies initialized +0ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] LoggerModule dependencies initialized +1ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] ConfigModule dependencies initialized +0ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] ConfigModule dependencies initialized +0ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [InstanceLoader] KyselyCoreModule dependencies initialized +0ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [RoutesResolver] AppController {/}: +3ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [RouterExplorer] Mapped {/, GET} route +1ms
[Nest] 24965  - 08/05/2024, 5:37:05 PM     LOG [NestApplication] Nest application successfully started +1ms
✔  TSC  Initializing type checker...
>  TSC  Found 0 issues.

@kdy1, do you know what the problem might be? I would love to help with this investigation, because I don't understand what's wrong here.

[lintellme99]

@kdy1 I have "fixed" that bug in this branch: https://github.com/lintellme99/nestjs-swc-bug/tree/without_bug

Now it works fine, but, I want it also work correctly on a small projects, that has a less than 30 files that swc should handle

[simplenotezy]

Nice find @lintellme99 - @kdy1 I know you must be super busy, but let me know if you need any help getting this in!

[kdy1]

It's not a bug of SWC. Also, please provide a SWC repro, not nestjs repro

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.