fix(bun): respect loader returned from load hook + feat(bun): support plugin.bun.loader for per-plugin loader resolution

[81reap]

I am volunteering and working on getting a bun plugin for TanStack/router and found this bug.

• Add router-plugin for bun bundler TanStack/router#6871 (comment)
• Bun adapter: load hook cannot override the inferred Loader #600

Summary by CodeRabbit

• New Features

  • Load hooks can now return an explicit loader override; plugin configuration may also supply a loader value or function to determine a module's loader.

• Tests

  • Added unit tests covering loader selection and precedence for virtual modules, ensuring hook-provided loaders take priority over inferred or configured loaders.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 67384b07-48e8-4273-a963-feab001f55ce

📥 Commits

Reviewing files that changed from the base of the PR and between 50d8d7c and 7668984.

📒 Files selected for processing (4)

• src/bun/index.ts
• src/bun/utils.ts
• src/types.ts
• test/unit-tests/bun/nested.test.ts

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📝 Walkthrough

Walkthrough

Adds LoadResult and unwrapLoader; Bun adapter records load-hook-provided loader and active plugin, then selects loader with precedence: load-hook override → plugin.bun.loader (possibly invoked) → original loader → guessLoader(id). Tests cover virtual-module loader resolution and precedence.

Changes

Bun Loader Override Support

Layer / File(s)	Summary
LoadResult type contract and hook signature src/types.ts	Bun Loader imported as BunLoader; new LoadResult extends the transform result object with optional loader?: BunLoader; HookFnMap.load now returns Thenable<LoadResult>.
unwrapLoader helper src/bun/utils.ts	Exported unwrapLoader(loader, code, id) that invokes a functional Bun loader with (code, id) or returns the loader value unchanged.
Bun adapter loader extraction and selection src/bun/index.ts	processLoadTransform records activePlugin and loaderOverride from load hook results, types handler returns as LoadResult, and selects final loader using precedence: loaderOverride → unwrapLoader(plugin.bun.loader, code, id) → original loader arg → guessLoader(id).
Test coverage for loader precedence test/unit-tests/bun/nested.test.ts	Adds tests for load-hook-provided loader, static plugin.bun.loader, functional plugin.bun.loader invocation, and precedence when both hook and plugin loader exist.

Sequence Diagram

sequenceDiagram
  participant Plugin as Plugin.load hook
  participant Adapter as Bun adapter (processLoadTransform)
  participant Unwrap as unwrapLoader
  Plugin->>Adapter: return { code, loader? } | or string code
  Adapter->>Adapter: record loaderOverride, activePlugin
  Adapter->>Unwrap: call unwrapLoader(plugin.bun.loader, code, id)
  Unwrap-->>Adapter: resolved plugin loader
  Adapter-->>Caller: return contents and chosen loader (loaderOverride || pluginLoader || originalLoader || guessLoader)

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• sxzz

Poem

🐰 I nibble code with careful hops,
LoadResult gives loader props,
Adapter listens, notes the cue,
unwraps plugin loaders too,
Hooks decide which loader pops!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the two main changes: fixing loader respect from load hooks and adding plugin.bun.loader support for per-plugin loader resolution.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 ESLint

If the error stems from missing dependencies, add them to the package.json file. For unrecoverable errors (e.g., due to private dependencies), disable the tool in the CodeRabbit configuration.

src/bun/index.ts

ESLint skipped: missing config or dependency (missing-dependency). The ESLint configuration references a package that is not available in the sandbox.

src/bun/utils.ts

ESLint skipped: the ESLint configuration for this file references a package that is not available in the sandbox.

src/types.ts

ESLint skipped: the ESLint configuration for this file references a package that is not available in the sandbox.

• 1 others

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[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/unplugin@601

commit: 7668984

[81reap]

@sxzz I've updated the commit message and fixed the merge conflict, lmk if there's any more feedback :)