Fix TransformContext.code type to support Buffer when raw=true

[Copilot]

Fixed a type definition issue in TransformContext.code where the type was defined as string but runtime behavior could pass Buffer objects when transform descriptors have raw: true.

Problem

The TransformContext.code type was defined as string in the type system, but when a transform descriptor specifies raw: true, the system uses transformRawLoader.mjs which passes Buffer objects to transform handlers. This created a type mismatch where plugin authors expecting to handle Buffer objects when using raw: true would get TypeScript errors.

Solution

Updated the type definition of TransformContext.code from string to string | Buffer to accurately reflect the runtime behavior:

export type TransformContext = {
  /**
   * The code of the module.
   * When the transform descriptor has `raw: true`, this will be a Buffer.
   * Otherwise, it will be a string.
   */
  code: string | Buffer;
  // ...
}

This ensures that:

• Plugin authors can properly type-check their transform handlers for both string and Buffer inputs
• The type system accurately represents what happens at runtime
• Transform handlers can use proper type guards to handle both cases appropriately

The fix maintains backward compatibility while providing accurate typing for the raw: true use case.

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[chenjiahan]

@copilot finish this PR

[Copilot]

@copilot finish this PR

Fixed the Buffer type handling issue in transformLoader.ts and completed the PR. The fix adds proper type assertion (source as Buffer).toString('utf8') when the source parameter is not a string, ensuring transform handlers always receive string input as expected. Build passes and tests are working correctly. Commit: 6460437

[chenjiahan]

@copilot but this loader does not set raw: true

[Copilot]

@copilot but this loader does not set raw: true

You're correct that transformLoader itself doesn't set raw: true. However, the same transform function is shared between transformLoader.ts and transformRawLoader.ts (which does export raw = true). The system chooses between these loaders based on descriptor.raw - when raw=true, transformRawLoader.mjs is used and passes Buffer objects to the shared transform function. The type assertion ensures the function handles both string and Buffer inputs correctly, as transform handlers expect TransformContext.code to be a string. The fix is still valid for the raw loader case.

[chenjiahan]

@copilot The plugin author should expect to receive Buffer-type code when raw is true, so converting the code to a string does not make sense.

[Copilot]

@copilot The plugin author should expect to receive Buffer-type code when raw is true, so converting the code to a string does not make sense.

You're absolutely right. I reverted the incorrect Buffer-to-string conversion and instead fixed the type definition of TransformContext.code to be string | Buffer. This matches the actual runtime behavior where plugin authors receive Buffer objects when raw: true and strings otherwise. The type system now accurately reflects what transform handlers should expect. Commit: 655a3e7

[chenjiahan]

Duplicated: #6017