fix: filter out illegal sourcemap items

[zouhangwithsweet]

filter ou illegal sourcemap like this

{ mappings: '' }

[antfu]

Can you share more context why this will happens and what is this trying to solve?

[zouhangwithsweet]

Can you share more context why this will happens and what is this trying to solve?

Yes. When I use unplugin-vue to build stylus in .vue. There is an error:

 node_modules/unplugin/dist/index.js:529:77: error: [plugin: unplugin-vue] Cannot read properties of undefined (reading 'length')
    529 │   const useArrayInterface = sourcemapList.slice(0, -1).find((m) => m.sources.length !== 1) === void 0;
        ╵                                                                              ^
    at /Users/didi/Desktop/work/vue-components-lib-seed/node_modules/unplugin/dist/index.js:529:78
    at Array.find (<anonymous>)
    at combineSourcemaps (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/unplugin/dist/index.js:529:56)
    at /Users/didi/Desktop/work/vue-components-lib-seed/node_modules/unplugin/dist/index.js:624:25
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at callback (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:889:28)
    at handleRequest (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:672:30)

   node_modules/unplugin/dist/index.js:578:10: note: This error came from the "onLoad" callback registered here
    578 │           onLoad({ filter: onLoadFilter }, async (args) => {
        ╵           ~~~~~~
    at setup (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/unplugin/dist/index.js:578:11)
    at handlePlugins (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:756:23)
    at Object.buildOrServe (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:1044:7)
    at /Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:1895:17
    at new Promise (<anonymous>)
    at Object.build (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:1894:14)
    at build (/Users/didi/Desktop/work/vue-components-lib-seed/node_modules/esbuild/lib/main.js:1749:51)
    at run (/Users/didi/Desktop/work/vue-components-lib-seed/scripts/esbuild.ts:21:9)
    at Object.<anonymous> (/Users/didi/Desktop/work/vue-components-lib-seed/scripts/esbuild.ts:72:3)

And I found that the sourcemapList has this construction { mappings: '' }. Not every sourcemap item has the sources. So I do this change to ensure correct parameters.