fix: correctly emit middleware file name

[ematipico]

Changes

The emission of the middleware file during the build still needed to be corrected. The code was working as expected, but the middleware.mjs wasn't emitted as expected, so I had to refactor how the plugin-middleware.ts works.

Notable changes:

• the middleware plugin is now a virtual module;
• the plugin must always emit correct code, even when no middleware exists. Because of that, when there's no middleware file present on file system, the plugin emits "no-op" code;
• the previous code was emitting the middleware code using the wild-card import/export e.g. import * as middleware. This wasn't ideal. When doing so, rollup creates a new export, which could cause some issue in the future;
• now the middleware wrapper is not present anymore, and because of that, I had to review the types inside the code;

This change is needed for other adapters to pick up the emitted code in a predictable way.

Testing

Current tests should pass

Docs

N/A

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[bluwy]

Couple suggestions below to make it more Rollup-style. In the future, I think we can also look into using this.emitFile to emit a new chunk instead, so we don't have to specify a rollup input and configure entryFileNames

[ematipico]

Couple suggestions below to make it more Rollup-style. In the future, I think we can also look into using this.emitFile to emit a new chunk instead, so we don't have to specify a rollup input and configure entryFileNames

Would that work? I would aim to emit an entry point, not a chunk.

[bluwy]

Nice the new refactor looks great now.

Would that work? I would aim to emit an entry point, not a chunk.

It should be possible to be used as an entrypoint too as long as you call emitFile with preserveSignatures: 'strict'