vp migrate rewrites catalog: specs in a Bun project whose workspaces.packages is empty #3375

Describe the bug

In a single-package Bun project that keeps its toolchain in workspaces.catalog with an empty workspaces.packages array, vp migrate handles the project as if it had no catalog support. It replaces every catalog: reference in devDependencies, and the catalog-valued entries in overrides, with concrete versions. workspaces.catalog stays in package.json, but nothing references it anymore.

Bun resolves this setup: bun install succeeds and vite resolves to @voidzero-dev/vite-plus-core. Bun only needs the root package.json to have a workspaces field; without one it fails with catalogs require a "workspaces" field in the root package.json. "workspaces": [] and "workspaces": { "packages": [] } both work.

The check that rejects this setup is bunWorkspaceDeclaresPackages() in packages/cli/src/migration/migrator/vite-plus-bootstrap.ts, which requires a non-empty package list. The comment above it says Bun resolves catalog: references only inside a workspace whose root package.json declares a non-empty workspaces. Bun 1.4.4 does not behave that way.

Reproduction

package.json:

{
  "name": "bun-root-catalog",
  "private": true,
  "type": "module",
  "packageManager": "bun@1.4.4",
  "devDependencies": {
    "@vitest/coverage-v8": "catalog:",
    "vite": "catalog:",
    "vite-plus": "catalog:",
    "vitest": "catalog:"
  },
  "workspaces": {
    "packages": [],
    "catalog": {
      "@vitest/coverage-v8": "5.1.0",
      "vite": "npm:@voidzero-dev/vite-plus-core@1.5.0",
      "vite-plus": "1.5.0",
      "vitest": "5.1.0"
    }
  },
  "overrides": {
    "vite": "catalog:",
    "vitest": "catalog:"
  }
}

printf 'node_modules\n' > .gitignore
bun install
git init && git add -A && git commit -m init
vp migrate --no-interactive --no-hooks --no-agent --no-editor
git diff package.json

Actual: bun install succeeds before the migration. Afterwards devDependencies become "@vitest/coverage-v8": "5.1.0", "vite": "npm:@voidzero-dev/vite-plus-core@1.5.0", "vite-plus": "1.5.0" and "vitest": "5.1.0", and overrides become "vite": "npm:@voidzero-dev/vite-plus-core@1.5.0" and "vitest": "5.1.0". The catalog is left unused.

Expected: no changes. With only "packages": [] changed to "packages": ["packages/*"], and no packages directory at all, the same command prints This project is already using Vite+! Happy coding! and leaves package.json as it is.

Suggested fix

For Bun, treat any root workspaces field (array or object form) as catalog support, which matches the check Bun itself applies, instead of requiring a non-empty package list.

Environment

• vite-plus 1.5.0 (global and local)
• Bun 1.4.4
• Node 26.13.0
• macOS arm64

Related, but different: #1247 (object-form workspaces, fixed in #1250) and #2309 (vp up rewriting catalog: specs in a monorepo). I have not checked Bun versions older than 1.4.4.