`bundleConfigFile` incorrectly resolves source map path under certain conditions

[Wakeful-Cloud]

Describe the bug

The path.resolve call inside of the sourcemapPathTransform callback in bundleConfigFile fails to resolve the correct configuration file path under certain circumstances (e.g., VitePress) due to incorrectly treating the last path segment as a directory, rather than a file. This sometimes results in the source map containing an incorrect path to the source file, which breaks debugging functionality in the config, as well as any plugins the config imports.

VitePress Behavior

Below is a screenshot of bundleConfigFile when resolving a VitePress config file:

Note the double .vitepress in the path, which is incorrect (It should just be /home/wakeful-cloud/Downloads/test/.vitepress/config.mts).

When I decode the base64-encoded source map at the bottom of the compiled config file, I predictably get a sourcemap with an incorrect path:

{
  "version": 3,
  "file": "config.js",
  "names": [],
  "sources": [
    "/home/wakeful-cloud/Downloads/test/.vitepress/.vitepress/config.mts"
  ],
  "sourcesContent": [
    "import { defineConfig } from 'vitepress'\n\n// https://vitepress.dev/reference/site-config\nexport default defineConfig({\n  title: \"My Awesome Project\",\n  description: \"A VitePress Site\",\n  vite: {\n    plugins: [\n      {\n        name: \"test\",\n        configResolved: config => {\n          console.log(\"Vite config resolved:\", config);\n        }\n      }\n    ]\n  },\n  themeConfig: {\n    // https://vitepress.dev/reference/default-theme-config\n    nav: [\n      { text: 'Home', link: '/' },\n      { text: 'Examples', link: '/markdown-examples' }\n    ],\n\n    sidebar: [\n      {\n        text: 'Examples',\n        items: [\n          { text: 'Markdown Examples', link: '/markdown-examples' },\n          { text: 'Runtime API Examples', link: '/api-examples' }\n        ]\n      }\n    ],\n\n    socialLinks: [\n      { icon: 'github', link: 'https://github.com/vuejs/vitepress' }\n    ]\n  }\n})\n"
  ],
  "mappings": ";;AAGA,IAAA,iBAAe,aAAa;CAC1B,OAAO;CACP,aAAa;CACb,MAAM,EACJ,SAAS,CACP;EACE,MAAM;EACN,iBAAgB,WAAU;GACxB,QAAQ,IAAI,yBAAyB,MAAM;EAC7C;CACF,CACF,EACF;CACA,aAAa;EAEX,KAAK,CACH;GAAE,MAAM;GAAQ,MAAM;EAAI,GAC1B;GAAE,MAAM;GAAY,MAAM;EAAqB,CACjD;EAEA,SAAS,CACP;GACE,MAAM;GACN,OAAO,CACL;IAAE,MAAM;IAAqB,MAAM;GAAqB,GACxD;IAAE,MAAM;IAAwB,MAAM;GAAgB,CACxD;EACF,CACF;EAEA,aAAa,CACX;GAAE,MAAM;GAAU,MAAM;EAAqC,CAC/D;CACF;AACF,CAAC"
}

Vanilla Vite Behavior

Interestingly, vanilla (i.e., non-VitePress) Vite does not experience this bug by coincidence. Below is a screenshot of bundleConfigFile when resolving a vanilla Vite config file:

This time, when I decode the source map, the path is correct:

{
  "version": 3,
  "file": "vite.config.js",
  "names": [],
  "sources": [
    "/home/wakeful-cloud/Downloads/test2/vite.config.ts"
  ],
  "sourcesContent": [
    "import { defineConfig } from \"vite\";\nimport vue from \"@vitejs/plugin-vue\";\n\n// https://vite.dev/config/\nexport default defineConfig({\n  plugins: [\n    vue(),\n    {\n      name: \"test\",\n      configResolved: (config) => {\n        console.log(\"Vite config resolved:\", config);\n      },\n    },\n  ],\n});\n"
  ],
  "mappings": ";;;AAIA,IAAA,sBAAe,aAAa,EAC1B,SAAS,CACP,IAAI,GACJ;CACE,MAAM;CACN,iBAAiB,WAAW;EAC1B,QAAQ,IAAI,yBAAyB,MAAM;CAC7C;AACF,CACF,EACF,CAAC"
}

And, debugging works as expected.

Workaround

If using VS Code, you can use sourceMapPathOverrides option in the launch config to alias the incorrect path to the correct path.

Reproduction

https://github.com/vuejs/vitepress

Steps to reproduce

Setup a vanilla VitePress project with TypeScript (i.e., npx vitepress init). Then, run VitePress with a debugger. For example, if using VS Code, create a .vscode/launch.json file with the below content:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Run Dev",
      "request": "launch",
      "runtimeArgs": [
        "run-script",
        "docs:dev"
      ],
      "runtimeExecutable": "npm",
      "skipFiles": [
        "<node_internals>/**"
      ],
      "resolveSourceMapLocations": [
        "${workspaceFolder}/node_modules/.vite-temp/**/*.mjs",
      ],
      // Workaround
      // "sourceMapPathOverrides": {
      //   "${workspaceFolder}/.vitepress/*": "${workspaceFolder}/*"
      // },
      "type": "node"
    }
  ],
  "compounds": []
}

and run the Run Dev configuration. None of the breakpoints set in the VitePress config (.vitepress/config.mts), nor any TypeScript file imported by the VitePress config will bind.

System Info

System:
    OS: Linux 7.0 Ubuntu 26.04 LTS 26.04 LTS (Resolute Raccoon)
    CPU: (16) x64 AMD
    Memory: 4.32 GB / 17.88 GB
    Container: Yes
    Shell: 5.3.9 - /bin/bash
  Binaries:
    Node: 24.16.0 - /run/user/1000/fnm_multishells/129123_1786504999833/bin/node
    npm: 11.13.0 - /run/user/1000/fnm_multishells/129123_1786504999833/bin/npm
  npmPackages:
    @vitejs/plugin-vue: ^6.0.8 => 6.0.8 
    vite: ^8.2.0 => 8.2.0 

Used Package Manager

npm

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[SnowingFox]

Opened a PR to address this: #23240

[Wakeful-Cloud]

I'm pretty sure just adding a path.dirname as both of the above PRs do will fix the VitePress behavior at the expense of breaking the vanilla Vite behavior. I believe the fix is a bit more involved.