Issue with .svelte.js files and Svelte 5

[andersekdahl]

This might not be a problem in svelte-loader but rather in the svelte compiler, but the issue shows itself in svelte-loader.

When I created a xxx.svelte.js file which got included in my webpack build I started getting a wierd error about Error: callback(): The callback was already called.. But that error turned out to not be the real error, it was just that an error was thrown here:

svelte-loader/index.js

Line 97 in f2a7bc1

callback(null, js.code, js.map);

Which triggered this line:

svelte-loader/index.js

Line 101 in f2a7bc1

callback(new Error(`${err.name}: ${err.toString()}`));

And since the error occured inside the callback the error became callback(): The callback was already called.

The real error was:

TypeError: Cannot read properties of null (reading 'startsWith')
    at contextifySourceUrl (/home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/webpack/lib/NormalModule.js:124:13)
    at /home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/webpack/lib/NormalModule.js:154:3
    at Array.map (<anonymous>)
    at contextifySourceMap (/home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/webpack/lib/NormalModule.js:153:39)
    at NormalModule.createSource (/home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/webpack/lib/NormalModule.js:799:5)
    at processResult (/home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/webpack/lib/NormalModule.js:870:24)
    at /home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/webpack/lib/NormalModule.js:964:5
    at /home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/loader-runner/lib/LoaderRunner.js:407:3
    at iterateNormalLoaders (/home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/loader-runner/lib/LoaderRunner.js:233:10)
    at iterateNormalLoaders (/home/anders.ekdahl/source/stickerapp/olympus/atlas/node_modules/loader-runner/lib/LoaderRunner.js:240:10)

I don't know what the cause is here, but if I stop passing js.map to callback() the error goes away so I guess it's something with Svelte 5s sourcemaps for .svelte.js files that causes it.

This is the contents of js.map when the error happens:

{
  version: 3,
  names: [],
  sources: [ null ],
  sourcesContent: [ null ],
  mappings: ';;;aAAa,OAAO;uBACG,IAAI;;KAAvB,SAAS;;;;KAAT,SAAS;;;;6BACgB,KAAK;;KAA9B,eAAe;;;;KAAf,eAAe;;;;6BACU,KAAK;;KAA9B,eAAe;;;;KAAf,eAAe;;;;CACf,eAAe;;;KACf,4BAA4B;;;;KAA5B,4BAA4B;;;;;;KAC5B,6BAA6B;;;;KAA7B,6BAA6B;;;;;;KAC7B,gBAAgB;;;;KAAhB,gBAAgB;;;;;;KAChB,qBAAqB;;;;KAArB,qBAAqB;;;;;;KACrB,yBAAyB;;;;KAAzB,yBAAyB;;;;;;KACzB,6BAA6B;;;;KAA7B,6BAA6B;;;;;;KAC7B,oCAAoC;;;;KAApC,oCAAoC;;;;;SAExB,IAAI,CAAC,qBAAqB,CAAC,MAAM,IACrC,IAAI,CAAC,yBAAyB,CAAC,MAAM,IACrC,IAAI,CAAC,6BAA6B,CAAC,MAAM,IACzC,MAAM,CAAC,IAAI,CAAC,IAAI,CAAC,oCAAoC,EAAE,MAAM;;;KAJrE,iBAAiB;;;;;QAYP,WAAW;;aACN,eAAe,IAAI,IAAI,CAAC,gBAAgB;SACzC,MAAM;OACR,UAAU,GAAG,CAAC;;cACP,IAAI,IAAI,eAAe,CAAC,KAAK;SAC/B,MAAM,CAAC,IAAI,CAAC,gBAAgB;KAC7B,MAAM,CAAC,IAAI,CAAC,gBAAgB,IAAI,CAAC;;;IAErC,MAAM,CAAC,IAAI,CAAC,gBAAgB;;QACxB,MAAM,CAAC,IAAI,CAAC,gBAAgB,IAAI,UAAU;KAC1C,UAAU,GAAG,MAAM,CAAC,IAAI,CAAC,gBAAgB;;;;GAGjD,WAAW,CAAC,eAAe,CAAC,EAAE,IAAI,UAAU;;;SAEzC,WAAW;;;KAhBtB,0BAA0B;;;;;QAsBhB,MAAM;;aACD,cAAc,IAAI,IAAI,CAAC,eAAe;SACvC,GAAG;IACL,cAAc;IACd,sBAAsB;IACtB,aAAa,EAAE,IAAI,CAAC,4BAA4B,EAAE,QAAQ,CAAC,cAAc,CAAC,EAAE,KAAK,KAAK;;;cAE/E,eAAe,IAAI,IAAI,CAAC,gBAAgB;UACzC,qBAAqB;KACvB,eAAe;KACf,KAAK,EAAE,IAAI,CAAC,qBAAqB,CAAC,QAAQ,CAAC,eAAe,CAAC,EAAE;KAC7D,OAAO;;;eAEA,mBAAmB,KAAK,eAAe,CAAC,KAAK,QAAQ,MAAM,EAAE,CAAC,KAAK,CAAC,CAAC,gBAAgB,KAAK,cAAc,CAAC,EAAE;WAC5G,KAAK,GAAG,IAAI,CAAC,yBAAyB,CAAC,QAAQ,CAAC,mBAAmB,CAAC,EAAE,KACxE,IAAI,CAAC,qBAAqB,CAAC,QAAQ,CAAC,eAAe,CAAC,EAAE;;KAC1D,qBAAqB,CAAC,OAAO,CAAC,IAAI;MAC9B,mBAAmB;MACnB,KAAK;MACL,QAAQ,GAAG,KAAK,MACV,IAAI,CAAC,oCAAoC,CAAC,mBAAmB,CAAC,EAAE;MACtE,aAAa,EAAE,IAAI,CAAC,6BAA6B,EAAE,QAAQ,CAAC,eAAe,CAAC,EAAE,KAC1E,KAAK;;;;;;UAKX,UAAU,GAAG,IAAI,CAAC,0BAA0B,CAAC,eAAe,CAAC,EAAE;;WAC9D,qBAAqB,CAAC,OAAO,CAAC,MAAM,GAAG,UAAU;KACpD,qBAAqB,CAAC,OAAO,CAAC,IAAI;MAC9B,mBAAmB,EAAE,SAAS;MAC9B,KAAK,EAAE,KAAK;MACZ,QAAQ,EAAE,KAAK;MACf,aAAa,EAAE,IAAI,CAAC,6BAA6B,EAAE,QAAQ,CAAC,eAAe,CAAC,EAAE,KAC1E,KAAK;;;;IAGjB,GAAG,CAAC,sBAAsB,CAAC,IAAI,CAAC,qBAAqB;;;GAEzD,MAAM,CAAC,IAAI,CAAC,GAAG;;;SAEZ,MAAM;;;KA1CjB,cAAc;;;;CA4Cd,WAAW;EAAC,eAAe;EAAE,2BAA2B;EAAE,0BAA0B;;EAChF,IAAI,CAAC,eAAe,GAAG,eAAe;;MAClC,2BAA2B;mDACU,2BAA2B;;;MAEhE,0BAA0B;kDACU,0BAA0B;;;'
}