declare const handled like const during analysis in Turbopack

[timneutkens]

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/eager-stonebraker-x42f67

To Reproduce

Reproduction requires #71802 to have landed first.

• Install next@canary
• Run next dev --turbo
• Open homepage /
• It should show my value instead of not set

Current vs. Expected behavior

Currently it shows not set when declare const MY_MAGIC_VARIABLE: string is in the file. Removing it shows the correct my value.

This code does not work with our define handling but works with webpack. When I remove the declare const it works. Looking at the AST output of SWC it seems declare const is a VariableDeclaration but has a property declare: true which it doesn't have for normal const assignment. Looking at the analyzer code we don't take declare: true into account so it's likely skipping replacement for define because we detect a VariableDeclaration already in scope so it doesn't replace.

AST snippet:

    {
      "type": "VariableDeclaration",
      "span": {
        "start": 0,
        "end": 25
      },
      "ctxt": 0,
      "kind": "const",
      "declare": true,
      "declarations": [

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Sun Aug  6 20:05:33 UTC 2023
  Available memory (MB): 4102
  Available CPU cores: 2
Binaries:
  Node: 20.9.0
  npm: 9.8.1
  Yarn: 1.22.19
  pnpm: 8.10.2
Relevant Packages:
  next: 15.0.4-canary.5 // Latest available version is detected (15.0.4-canary.5).
  eslint-config-next: N/A
  react: 19.0.0-rc-5c56b873-20241107
  react-dom: 19.0.0-rc-5c56b873-20241107
  typescript: 5.3.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Turbopack

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local)

Additional context

No response

[github-actions]

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