Source map line numbers are wrong when using typescript

[fd0]

Describe the bug
When using typescript within .svelte files, the generated source map references the wrong line number, it is too low.

To Reproduce

• Checkout the template and install libraries:

npx degit sveltejs/template svelte-typescript-app
cd svelte-typescript-app
npm install

• Modify the script in src/App.svelte like this:

<script>
    export let name;

    // test comment
    console.error("error logged from line five in App.svelte")
</script>

• Run the app and visit it in a browser, the following message is in the JavaScript console:

error logged from line five in App.svelte     App.svelte:5

• Now add TypeScript support according to the instructions in the blog:

node scripts/setupTypeScript.js
npm install

• Mark the script in src/App.svelte as TypeScript:

<script lang="ts">
    export let name;

    // test comment
    console.error("error logged from line five in App.svelte")
</script>

• Run the app, visit it again, find the following message in the browser console:

error logged from line five in App.svelte      App.svelte:3 

• Clicking on the file name takes me to line 3 of App.svelte:
  

I've published a reproduction repo here: https://github.com/fd0/svelte-bug-typescript-sourcemap (including package-lock.json).

Expected behavior

The error message should refer to the correct line in the source code (line 5 instead of line 3).

Information about your Svelte project:

• Chrome 83.0.4103.116
• Debian Buster
• Svelte 3.24.0
• Rollup 2.22.2

Severity

It's very annoying, but does not block me (or anybody else). Debugging takes much longer.

Additional context

Thank you very much for adding TypeScript to Svelte, I love it!

[benmccann]

Thanks for the issue report and help in reproducing this. If this only happens when using TypeScript you probably will get a better response filing this issue in the corresponding subproject. Though I'm not entirely sure whether that's https://github.com/sveltejs/svelte-preprocess or https://github.com/sveltejs/language-tools (if this is an issue in svelte2tsx) - you might want to ask in the #language-tools channel on Discord

[pngwn]

This is probably just because preprocessors don’t support sourcemaps. There is a PR for this somewhere.

[benmccann]

sveltejs/svelte-preprocess#171 says "Added general sourceMap: boolean prop to set source maps for all preprocessors." and the reproduction repo uses svelte-preprocess v4. I'm not quite sure from the description if that is set by default or not. Perhaps you could try adding that option to the rollup config to see if it changes anything?

[fd0]

Setting the sourceMap config to either true or false doesn't change anything:

            preprocess: sveltePreprocess({
                sourceMap: true,
            }),

Source maps are generated and reference the wrong line. Hm.

[Conduitry]

Any sourcemaps generated by svelte-preprocess (and I don't know that it is generating any) currently won't do anything because the main compiler doesn't handle inputting sourcemaps - and so the sourcemaps in the compiled components will point to lines in the already-preprocessed versions of the components. Support for this will need to be added in Svelte (there is a PR for this somewhere that hasn't been reviewed yet), and the bundler plugins will need to be updated to pass the sourcemaps from the preprocessor to the compiler, and also the preprocessor will need to actually return sourcemaps.

[benmccann]

Ah, thanks for the clarification. And here's the PR for reference: #5015

[Baxterboom]

I tried to check status on this, but gets lost in github refs. Are we close to a solution?

[samal-rasmussen]

I tried to check status on this, but gets lost in github refs. Are we close to a solution?

This PR with the bulk of the work, as far as I can see, is approved and waiting to be merged: #5584

So I believe the answer is yes we are close.

[milahu]

still an issue with import alias
this should also affect svelte-kit where import alias is used by default

repro

cd $(mktemp -d)
git clone https://github.com/milahu/svelte-web-desktop --branch debug-typescript-wrong-line-numbers
cd svelte-web-desktop
pnpm install
npm run dev

errors start at line 50

wallpaper.config.ts:1 src/configs/wallpapers/wallpaper.config.ts - line 1
wallpaper.config.ts:10 src/configs/wallpapers/wallpaper.config.ts - line 10
wallpaper.config.ts:20 src/configs/wallpapers/wallpaper.config.ts - line 20
wallpaper.config.ts:40 src/configs/wallpapers/wallpaper.config.ts - line 40
wallpaper.config.ts:43 src/configs/wallpapers/wallpaper.config.ts - line 50 -> 43
wallpaper.config.ts:71 src/configs/wallpapers/wallpaper.config.ts - line 80 -> 71
wallpaper.config.ts:440 src/configs/wallpapers/wallpaper.config.ts - line 500 -> 440

src/components/apps/WallpaperApp/Wallpaper.svelte

  import { wallpapersConfig } from '$src/configs/wallpapers/wallpaper.config';

relevant config ...

vite.config.ts

export default defineConfig({
  resolve: {
    alias: {
      '$src': path.resolve('./src')
    },
  },

tsconfig.json

{
  "compilerOptions": {
    //"baseUrl": ".",
    "paths": {
      "$src/*": ["src/*"]
    },
  },
}

i tried to patch alias imports to relative imports with
https://stackoverflow.com/questions/57188027/refactor-aliased-imports-to-relative-paths
but jscodeshift cannot parse *.svelte files

/*
https://stackoverflow.com/questions/57188027/refactor-aliased-imports-to-relative-paths

pnpm i -D jscodeshift @babel/core

# problem: jscodeshift cannot parse *.svelte files
npx jscodeshift --extensions=svelte --parser=svelte -t codemods/alias-to-relative-import.cjs src

# JS dryrun + print
npx jscodeshift -t codemods/alias-to-relative-import.cjs src -d -p

# JS
npx jscodeshift -t codemods/alias-to-relative-import.cjs src

# TS dryrun + print
npx jscodeshift --extensions=ts --parser=ts -t codemods/alias-to-relative-import.cjs src -d -p

# TS
npx jscodeshift --extensions=ts --parser=ts -t codemods/alias-to-relative-import.cjs src

*/

const path = require("path");

function replacePathAlias(currentFilePath, importPath, pathMap) {
  // if windows env, convert backslashes to "/" first
  currentFilePath = path.posix.join(...currentFilePath.split(path.sep));

  const regex = createRegex(pathMap);
  return importPath.replace(regex, replacer);

  function replacer(_, alias, rest) {
const mappedImportPath = pathMap[alias] + rest;

// use path.posix to also create foward slashes on windows environment
let mappedImportPathRelative = path.posix.relative(
  path.dirname(currentFilePath),
  mappedImportPath
);
// append "./" to make it a relative import path
if (!mappedImportPathRelative.startsWith("../")) {
  mappedImportPathRelative = `./${mappedImportPathRelative}`;
}

logReplace(currentFilePath, mappedImportPathRelative);

return mappedImportPathRelative;
  }
}

function createRegex(pathMap) {
  const mapKeysStr = Object.keys(pathMap).reduce((acc, cur) => `${acc}|${cur}`);
  const regexStr = `^(${mapKeysStr})(.*)$`;
  return new RegExp(regexStr, "g");
}

const log = true;
function logReplace(currentFilePath, mappedImportPathRelative) {
  if (log)
console.log(
  "current processed file:",
  currentFilePath,
  "; Mapped import path relative to current file:",
  mappedImportPathRelative
);
}

/**
 * Corresponds to tsconfig.json paths or webpack aliases
 * E.g. "@/app/store/AppStore" -> "./src/app/store/AppStore"
 */
const pathMapping = {
  //"@": "./src",
  //"foo": "bar",
  "$src": "./src",
};

module.exports = function transform(file, api) {
  const j = api.jscodeshift;
  const root = j(file.source);

  root.find(j.ImportDeclaration).forEach(replaceNodepathAliases);
  root.find(j.ExportAllDeclaration).forEach(replaceNodepathAliases);

  /**
   * Filter out normal module exports, like export function foo(){ ...}
   * Include export {a} from "mymodule" etc.
   */
  root
.find(j.ExportNamedDeclaration, (node) => node.source !== null)
.forEach(replaceNodepathAliases);

  return root.toSource();

  function replaceNodepathAliases(impExpDeclNodePath) {
impExpDeclNodePath.value.source.value = replacePathAlias(
  file.path,
  impExpDeclNodePath.value.source.value,
  pathMapping
);
  }
};

[umaranis]

@milahu I am facing the same issue

[benmccann]

@milahu this sounds like a bug in either Vite (e.g. this plugin) or @rollup/plugin-alias. It'd be great if you were able to narrow down which project is causing it! Thanks as always for your help improving source map support!

[umaranis]

@milahu @benmccann not sure it's relevant to this issue but I get the following warning from vite-plugin-svelte.
 WARN  deprecated sourcemap-codec@1.4.8: Please use @jridgewell/sourcemap-codec instead