---
title: Fix Vite 8 resolve.alias customResolver Removal
description: Fix Vite 8 removing resolve.alias customResolver, which breaks CSS/JS path-alias plugins. Astro's own core fix shows the replacement.
date: 2026-08-05T00:00:00.000Z
category: guides-fixes
tags: vite, rolldown, config, bug-fix
---

## Quick Answer

Vite 8 removes the `resolve.alias[].customResolver` hook entirely: "use a custom plugin with `resolveId` hook and `enforce: 'pre'` instead." Any alias-resolution plugin relying on the old hook needs rewriting as a real Vite plugin. Astro's own core hit this and already shipped the fix in 7.0.0 stable. See its `resolveId`-based replacement below.

## Why customResolver stopped working

Vite's `resolve.alias` option has always supported two shapes: a plain string/RegExp `find` and `replacement` pair (still fully supported in Vite 8), and a version that supplies its own `customResolver` function to override how Vite resolved that specific aliased path. [Vite's migration guide](https://vite.dev/guide/migration) lists the second form under "Deprecated Options," removed outright: "`resolve.alias[].customResolver`: use a custom plugin with `resolveId` hook and `enforce: 'pre'` instead."

Alias resolution is no longer an extension point in Vite 8. Any config or plugin that supplied a `customResolver` function silently stops taking effect. Vite doesn't error on the unrecognized option, it just never calls it, so the alias quietly resolves to nothing or falls through to a different resolution path.

Astro's own core hit this directly. Its tsconfig path-alias logic for CSS `@import` statements used `customResolver` internally. [PR #17090, "Fix Vite and Rolldown build warnings in Astro 7"](https://github.com/withastro/astro/pull/17090), merged 2026-06-18, replaced it with two separate plugins using `resolveId`/transform hooks instead, and shipped already-fixed in Astro 7.0.0 stable.

## Fix it: replace customResolver with a resolveId plugin

### Before: the removed pattern

```js title="vite.config.ts - Vite 7 pattern"
export default defineConfig({
  resolve: {
    alias: [
      {
        find: /^~(.+)/,
        replacement: "$1",
        customResolver(source) {
          // BROKEN in Vite 8: customResolver is no longer called
          return resolveTsconfigPath(source);
        },
      },
    ],
  },
});
```

### After: the same resolution logic, as a real plugin

```js title="vite.config.ts - Vite 8 pattern"
export default defineConfig({
  plugins: [
    {
      name: "tsconfig-alias",
      enforce: "pre",
      resolveId(source) {
        // FIXED: resolveId + enforce: 'pre' replaces the removed
        // resolve.alias[].customResolver hook, running before
        // Vite's own default resolution
        if (source.startsWith("~")) {
          return resolveTsconfigPath(source.slice(1));
        }
        return null;
      },
    },
  ],
});
```

`enforce: "pre"` matters here. Without it, your plugin's `resolveId` runs after Vite's built-in resolvers, by which point the aliased path may have already resolved (or failed to resolve) the wrong way, the same ordering guarantee `customResolver` used to provide implicitly.

## Confirmed version range

Verified against Astro's own real fix: [PR #17090](https://github.com/withastro/astro/pull/17090) merged 2026-06-18, shipped in Astro 7.0.0 stable, replacing the exact `customResolver` pattern shown above with a `resolveId`-based plugin for the same tsconfig-path-alias logic. If you're on Astro 7.0.0 or later, Astro's own core already handles this. This fix applies to your own project's Vite config or any third-party Vite plugin that still supplies a `customResolver` function. Browse more posts like this in the [Guides & Fixes](/guides-fixes) archive.